{"id":8348,"date":"2015-10-28T15:56:44","date_gmt":"2015-10-28T19:56:44","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/pathology\/chapter\/23-3-antibodies\/"},"modified":"2025-08-23T23:53:40","modified_gmt":"2025-08-24T03:53:40","slug":"23-3-antibodies","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/pathology\/chapter\/23-3-antibodies\/","title":{"raw":"Antibodies","rendered":"Antibodies"},"content":{"raw":"<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\">Learning Objectives<\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n\r\nBy the end of this section, you will be able to:\r\n<ul>\r\n \t<li class=\"listitem\">Explain cross-reactivity.<\/li>\r\n \t<li class=\"listitem\">Describe the structure and function of antibodies.<\/li>\r\n \t<li class=\"listitem\">Discuss antibody production.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\nAn <span id=\"m44823-autoid-cnx2dbk-id1550152\"><\/span>[pb_glossary id=\"8516\"]<span id=\"m44823-autoid-cnx2dbk-id1550152\"> <\/span>antibody[\/pb_glossary], also known as an immunoglobulin (Ig), is a protein that is produced by plasma cells after stimulation by an antigen. Antibodies are the functional basis of humoral immunity. Antibodies occur in the blood, in gastric and mucus secretions, and in breast milk. Antibodies in these bodily fluids can bind pathogens and mark them for destruction by phagocytes before they can infect cells.\r\n<div class=\"section\" title=\"Antibody Structure\">\r\n<div class=\"titlepage\">\r\n<div>\r\n<div>\r\n<h2 id=\"m44823-fs-idp96468480\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Antibody Structure<\/span><\/span><\/h2>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<span id=\"m44823-fs-idp142597072\"> <\/span>An antibody molecule is comprised of four polypeptides: two identical heavy chains (large peptide units) that are partially bound to each other in a \u201cY\u201d formation, which are flanked by two identical light chains (small peptide units). <span style=\"text-align: initial;font-size: 1em\">Bonds between the cysteine amino acids in the antibody molecule attach the polypeptides to each other. The areas where the antigen is recognized on the antibody are variable domains and the antibody base is composed of constant domains.<\/span>\r\n\r\n<\/div>\r\n<span id=\"m44823-fs-idm36621536\"> <\/span>In germ-line B cells, the variable region of the light chain gene has 40 variable (V) and five joining (J) segments. An enzyme called DNA recombinase randomly excises most of these segments out of the gene, and splices one V segment to one J segment. During RNA processing, all but one V and J segment are spliced out. Recombination and splicing may result in over 10<sup>6<\/sup> possible VJ combinations. As a result, each differentiated B cell in the human body typically has a unique variable chain. The constant domain, which does not bind antibody, is the same for all antibodies.\r\n\r\n&nbsp;\r\n\r\n[caption id=\"attachment_8344\" align=\"aligncenter\" width=\"959\"]<img class=\"wp-image-8344 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2015\/10\/Figure_42_03_01-959x1024-1.jpg\" alt=\"A two-panel figure describing the genetic basis of antibody diversity. Panel (a) shows the process of V(D)J recombination: a germ-line DNA configuration with multiple V, J, and C gene segments undergoes rearrangement, transcription, and RNA splicing to produce a final mRNA that codes for an antibody light chain. Panel (b) shows the resulting protein structure of a membrane-bound B cell receptor, composed of light and heavy chains with variable and constant regions forming antigen-binding sites.\" width=\"959\" height=\"1024\" \/> (a) As a germ-line B cell matures, an enzyme called DNA recombinase randomly excises V and J segments from the light chain gene. Splicing at the mRNA level results in further gene rearrangement. As a result, (b) each antibody has a unique variable region capable of binding a different antigen.[\/caption]\r\n\r\nSimilar to TCRs and BCRs, antibody diversity is produced by the mutation and recombination of approximately 300 different gene segments encoding the light and heavy chain variable domains in precursor cells that are destined to become B cells. The variable domains from the heavy and light chains interact to form the binding site through which an antibody can bind a specific epitope on an antigen. The numbers of repeated constant domains in Ig classes are the same for all antibodies corresponding to a specific class. Antibodies are structurally similar to the extracellular component of the BCRs, and B cell maturation to plasma cells can be visualized in simple terms as the cell acquires the ability to secrete the extracellular portion of its BCR in large quantities.\r\n<div id=\"m44823-fig-ch42_03_01\" class=\"figure\" title=\"Figure\u00a042.22.\u00a0\">\r\n<div class=\"section\" title=\"Antibody Classes\">\r\n<div class=\"titlepage\">\r\n<div>\r\n<div>\r\n<h2 id=\"m44823-fs-idm30804944\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Antibody Classes<\/span><\/span><\/h2>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<span id=\"m44823-fs-idp17788400\"> <\/span>Antibodies can be divided into five classes\u2014IgM, IgG, IgA, IgD, IgE\u2014based on their physiochemical, structural, and immunological properties. IgGs, which make up about 80 percent of all antibodies, have heavy chains that consist of one variable domain and three identical constant domains. IgA and IgD also have three constant domains per heavy chain, whereas IgM and IgE each have four constant domains per heavy chain. The variable domain determines binding specificity and the constant domain of the heavy chain determines the immunological mechanism of action of the corresponding antibody class. It is possible for two antibodies to have the same binding specificities but be in different classes and, therefore, to be involved in different functions.\r\n\r\n<span id=\"m44823-fs-idm60930656\"> <\/span>After an adaptive defense is produced against a pathogen, typically plasma cells first secrete IgM into the blood. BCRs on na\u00efve B cells are of the IgM class and occasionally IgD class. IgM molecules make up approximately ten percent of all antibodies. Prior to antibody secretion, plasma cells assemble IgM molecules into pentamers (five individual antibodies) linked by a joining (J) chain. The pentamer arrangement means that these macromolecules can bind ten identical antigens. However, IgM molecules released early in the adaptive immune response do not bind to antigens as stably as IgGs, which are one of the possible types of antibodies secreted in large quantities upon re-exposure to the same pathogen.\r\n\r\n[caption id=\"attachment_8345\" align=\"aligncenter\" width=\"1024\"]<img class=\"wp-image-8345 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_02-1024x556-1.jpg\" alt=\"A table summarizing the five classes of antibodies (immunoglobulins): IgA, IgD, IgE, IgG, and IgM. For each class, the table lists its key properties and functions in the immune system, such as location, role in protection, and special capabilities like crossing the placenta.\" width=\"1024\" height=\"556\" \/> Immunoglobulins have different functions, but all are composed of light and heavy chains that form a Y-shaped structure.[\/caption]\r\n\r\n<div id=\"m44823-fig-ch42_03_02\" class=\"figure\" title=\"Figure\u00a042.23.\u00a0\">\r\n\r\n<span id=\"m44823-fs-idp106928032\"> <\/span>IgAs populate the saliva, tears, breast milk, and mucus secretions of the gastrointestinal, respiratory, and genitourinary tracts. Collectively, these bodily fluids coat and protect the extensive mucosa (4000 square feet in humans). The total number of IgA molecules in these bodily secretions is greater than the number of IgG molecules in the blood serum. A small amount of IgA is also secreted into the serum in monomeric form. Conversely, some IgM is secreted into bodily fluids of the mucosa. Similar to IgM, IgA molecules are secreted as polymeric structures linked with a J chain. However, IgAs are secreted mostly as dimeric molecules, not pentamers.\r\n\r\n<span id=\"m44823-fs-idm5112096\"> <\/span>IgE is present in the serum in small quantities and is best characterized in its role as an allergy mediator. IgD is also present in small quantities. Similar to IgM, BCRs of the IgD class are found on the surface of na\u00efve B cells. This class supports antigen recognition and maturation of B cells to plasma cells.\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"section\" title=\"Antibody Functions\">\r\n<div class=\"titlepage\">\r\n<div>\r\n<div>\r\n<h2 id=\"m44823-fs-idp152771184\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Antibody Functions<\/span><\/span><\/h2>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<span id=\"m44823-fs-idm1203424\"> <\/span>Differentiated plasma cells are crucial players in the humoral response, and the antibodies they secrete are particularly significant against extracellular pathogens and toxins. Antibodies circulate freely and act independently of plasma cells. Antibodies can be transferred from one individual to another to temporarily protect against infectious disease. For instance, a person who has recently produced a successful immune response against a particular disease agent can donate blood to a nonimmune recipient and confer temporary immunity through antibodies in the donor\u2019s blood serum. This phenomenon is called <span id=\"m44823-autoid-cnx2dbk-id1612222\"><\/span>[pb_glossary id=\"8517\"]<span id=\"m44823-autoid-cnx2dbk-id1612222\"> <\/span>passive immunity[\/pb_glossary]; it also occurs naturally during breastfeeding, which makes breastfed infants highly resistant to infections during the first few months of life.\r\n\r\n<span id=\"m44823-fs-idp52929952\"> <\/span>Antibodies coat extracellular pathogens and neutralize them\u00a0by blocking key sites on the pathogen that enhance their infectivity (such as receptors that \u201cdock\u201d pathogens on host cells). Antibody neutralization can prevent pathogens from entering and infecting host cells, as opposed to the CTL-mediated approach of killing cells that are already infected to prevent progression of an established infection. The neutralized antibody-coated pathogens can then be filtered by the spleen and eliminated in urine or feces.\r\n\r\n[caption id=\"attachment_8346\" align=\"aligncenter\" width=\"544\"]<img class=\"wp-image-8346 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_03.jpg\" alt=\"A three-panel diagram illustrating the mechanisms of antibody action. Panel (a) Neutralization: Antibodies bind to a virus and a toxin, blocking them from attaching to host cells. Panel (b) Opsonization: Antibodies coat a pathogen, marking it for ingestion by a macrophage. Panel (c) Complement Activation: Antibodies bound to a pathogen's surface trigger the complement cascade, forming pores in the pathogen's membrane.\" width=\"544\" height=\"875\" \/> Antibodies may inhibit infection by (a) preventing the antigen from binding its target, (b) tagging a pathogen for destruction by macrophages or neutrophils, or (c) activating the complement cascade.[\/caption]\r\n\r\n<div id=\"m44823-fig-ch42_03_03\" class=\"figure\" title=\"Figure\u00a042.24.\u00a0\">\r\n\r\n<span id=\"m44823-fs-idm98879504\"> <\/span>Antibodies also mark pathogens for destruction by phagocytic cells, such as macrophages or neutrophils, because phagocytic cells are highly attracted to macromolecules complexed with antibodies. Phagocytic enhancement by antibodies is called opsonization. In a process called complement fixation, IgM and IgG in serum bind to antigens and provide docking sites onto which sequential complement proteins can bind. The combination of antibodies and complement enhances opsonization even further and promotes rapid clearing of pathogens.\r\n<div class=\"section\" title=\"Affinity, Avidity, and Cross Reactivity\">\r\n<div class=\"titlepage\">\r\n<div>\r\n<div>\r\n<h2 id=\"m44823-fs-idp128057760\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Affinity, Avidity, and Cross Reactivity<\/span><\/span><\/h2>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<span id=\"m44823-fs-idp130541824\"> <\/span>Not all antibodies bind with the same strength, specificity, and stability. In fact, antibodies exhibit different <span id=\"m44823-autoid-cnx2dbk-id1634621\"><\/span>[pb_glossary id=\"8518\"]<span id=\"m44823-autoid-cnx2dbk-id1634621\"> <\/span>affinities[\/pb_glossary]\u00a0(attraction) depending on the molecular complementarity between antigen and antibody molecules. An antibody with a higher affinity for a particular antigen would bind more strongly and stably, and thus would be expected to present a more challenging defense against the pathogen corresponding to the specific antigen.\r\n\r\n[caption id=\"attachment_8347\" align=\"aligncenter\" width=\"544\"]<img class=\"wp-image-8347 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_04.jpg\" alt=\"A two-panel diagram explaining antibody binding concepts. Panel (a) contrasts affinity (the strength of a single antigen-binding site interaction, high in IgG) with avidity (the combined strength of all binding sites, high in IgM due to its ten binding sites). Panel (b) illustrates cross-reactivity, where a single antibody can bind to two different, but structurally similar, antigenic epitopes.\" width=\"544\" height=\"892\" \/> (a) Affinity refers to the strength of single interaction between antigen and antibody, while avidity refers to the strength of all interactions combined. (b) An antibody may cross react with different epitopes.[\/caption]\r\n\r\n<div id=\"m44823-fig-ch42_03_04\" class=\"figure\" title=\"Figure\u00a042.25.\u00a0\">\r\n\r\n<span id=\"m44823-fs-idp123736016\"> <\/span>The term <span id=\"m44823-autoid-cnx2dbk-id1299871\"><\/span>[pb_glossary id=\"8519\"]<span id=\"m44823-autoid-cnx2dbk-id1299871\"> <\/span>avidity[\/pb_glossary]\u00a0describes binding by antibody classes that are secreted as joined, multivalent structures (such as IgM and IgA). Although avidity measures the strength of binding, just as affinity does, the avidity is not simply the sum of the affinities of the antibodies in a multimeric structure. The avidity depends on the number of identical binding sites on the antigen being detected, as well as other physical and chemical factors. Typically, multimeric antibodies, such as pentameric IgM, are classified as having lower affinity than monomeric antibodies, but high avidity. Essentially, the fact that multimeric antibodies can bind many antigens simultaneously balances their slightly lower binding strength for each antibody\/antigen interaction.\r\n\r\n<span id=\"m44823-fs-idp95317264\"> <\/span>Antibodies secreted after binding to one epitope on an antigen may exhibit cross reactivity for the same or similar epitopes on different antigens. Because an epitope corresponds to such a small region (the surface area of about four to six amino acids), it is possible for different macromolecules to exhibit the same molecular identities and orientations over short regions. <span id=\"m44823-autoid-cnx2dbk-id1520463\"><\/span>[pb_glossary id=\"8520\"]<span id=\"m44823-autoid-cnx2dbk-id1520463\"> <\/span>Cross reactivity[\/pb_glossary]\u00a0describes when an antibody binds not to the antigen that elicited its synthesis and secretion, but to a different antigen.\r\n\r\n<span id=\"m44823-fs-idm96333024\"> <\/span>Cross reactivity can be beneficial if an individual develops immunity to several related pathogens despite having only been exposed to or vaccinated against one of them. For instance, antibody cross reactivity may occur against the similar surface structures of various Gram-negative bacteria. Conversely, antibodies raised against pathogenic molecular components that resemble self molecules may incorrectly mark host cells for destruction and cause autoimmune damage. Patients who develop systemic lupus erythematosus (SLE) commonly exhibit antibodies that react with their own DNA. These antibodies may have been initially raised against the nucleic acid of microorganisms but later cross-reacted with self-antigens. This phenomenon is also called molecular mimicry.\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"section\" title=\"Antibodies of the Mucosal Immune System\">\r\n<div class=\"titlepage\">\r\n<div>\r\n<div>\r\n<h2 id=\"m44823-fs-idp31880336\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Antibodies of the Mucosal Immune System<\/span><\/span><\/h2>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<span id=\"m44823-fs-idm58914256\"> <\/span>Antibodies synthesized by the mucosal immune system include IgA and IgM. Activated B cells differentiate into mucosal plasma cells that synthesize and secrete dimeric IgA, and to a lesser extent, pentameric IgM. Secreted IgA is abundant in tears, saliva, breast milk, and in secretions of the gastrointestinal and respiratory tracts. Antibody secretion results in a local humoral response at epithelial surfaces and prevents infection of the mucosa by binding and neutralizing pathogens.\r\n<h2>Review Section<\/h2>\r\nAntibodies (immunoglobulins) are the molecules secreted from plasma cells that mediate the humoral immune response. There are five antibody classes; an antibody's class determines its mechanism of action and production site but does not control its binding specificity. Antibodies bind antigens via variable domains and can either neutralize pathogens or mark them for phagocytosis or activate the complement cascade.\r\n<div class=\"textbox exercises\">\r\n<h3>Exercises<\/h3>\r\n<ol>\r\n \t<li>The structure of an antibody is similar to the extracellular component of which receptor?\r\n<ol>\r\n \t<li>MHC I<\/li>\r\n \t<li>MHC II<\/li>\r\n \t<li>BCR<\/li>\r\n \t<li>none of the above<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li><span id=\"m44823-fs-idm96383840\"><span id=\"m44823-fs-idp15569584\">The first antibody class to appear in the serum in response to a newly encountered pathogen is ________.<\/span><\/span>\r\n<ol>\r\n \t<li>IgM<\/li>\r\n \t<li>IgA<\/li>\r\n \t<li>IgG<\/li>\r\n \t<li>IgE<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li><span id=\"m44823-fs-idm117586432\"><span id=\"m44823-fs-idp32974160\">What is the most abundant antibody class detected in the serum upon reexposure to a pathogen or in reaction to a vaccine?<\/span><\/span>\r\n<ol>\r\n \t<li>IgM<\/li>\r\n \t<li>IgA<\/li>\r\n \t<li>IgG<\/li>\r\n \t<li>IgE<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li><span id=\"m44823-fs-idm103783696\"><span id=\"m44823-fs-idp49564592\">Breastfed infants typically are resistant to disease because of ________.<\/span><\/span>\r\n<ol>\r\n \t<li>active immunity<\/li>\r\n \t<li>passive immunity<\/li>\r\n \t<li>immune tolerance<\/li>\r\n \t<li>immune memory<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li><span id=\"m44823-fs-idm59001040\"><span id=\"m44823-fs-idm35976544\">What are the benefits and costs of antibody cross reactivity?<\/span><\/span><\/li>\r\n<\/ol>\r\n<strong>Answers<\/strong>\r\n<ol>\r\n \t<li>C<\/li>\r\n \t<li>A<\/li>\r\n \t<li>C<\/li>\r\n \t<li>B<\/li>\r\n \t<li>Cross reactivity of antibodies can be beneficial when it allows an individual's immune system to respond to an array of similar pathogens after being exposed to just one of them. A potential cost of cross reactivity is an antibody response to parts of the body (self) in addition to the appropriate antigen.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<h1>Adaptation<\/h1>\r\n<span style=\"text-align: initial;font-size: 1em\">This chapter was adapted by Morgan Alford from the following text:<\/span>\r\n\r\n<a href=\"https:\/\/opentextbc.ca\/biology\/part\/chapter-23-the-immune-system\/\">The Immune System<\/a> in <a href=\"https:\/\/opentextbc.ca\/biology\/\">Concepts of Biology, First Canadian Edition<\/a> by Drs. Jane Gair and Charles Molnar is licensed under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">Creative Commons Attribution 4.0 International License<\/a>.<span style=\"font-family: 'Cormorant Garamond', serif;font-size: 2.666667em;text-align: center\">\u00a0<\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>","rendered":"<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\">Learning Objectives<\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li class=\"listitem\">Explain cross-reactivity.<\/li>\n<li class=\"listitem\">Describe the structure and function of antibodies.<\/li>\n<li class=\"listitem\">Discuss antibody production.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<p>An <span id=\"m44823-autoid-cnx2dbk-id1550152\"><\/span><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_8348_8516\"><span id=\"m44823-autoid-cnx2dbk-id1550152\"> <\/span>antibody<\/a>, also known as an immunoglobulin (Ig), is a protein that is produced by plasma cells after stimulation by an antigen. Antibodies are the functional basis of humoral immunity. Antibodies occur in the blood, in gastric and mucus secretions, and in breast milk. Antibodies in these bodily fluids can bind pathogens and mark them for destruction by phagocytes before they can infect cells.<\/p>\n<div class=\"section\" title=\"Antibody Structure\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44823-fs-idp96468480\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Antibody Structure<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44823-fs-idp142597072\"> <\/span>An antibody molecule is comprised of four polypeptides: two identical heavy chains (large peptide units) that are partially bound to each other in a \u201cY\u201d formation, which are flanked by two identical light chains (small peptide units). <span style=\"text-align: initial;font-size: 1em\">Bonds between the cysteine amino acids in the antibody molecule attach the polypeptides to each other. The areas where the antigen is recognized on the antibody are variable domains and the antibody base is composed of constant domains.<\/span><\/p>\n<\/div>\n<p><span id=\"m44823-fs-idm36621536\"> <\/span>In germ-line B cells, the variable region of the light chain gene has 40 variable (V) and five joining (J) segments. An enzyme called DNA recombinase randomly excises most of these segments out of the gene, and splices one V segment to one J segment. During RNA processing, all but one V and J segment are spliced out. Recombination and splicing may result in over 10<sup>6<\/sup> possible VJ combinations. As a result, each differentiated B cell in the human body typically has a unique variable chain. The constant domain, which does not bind antibody, is the same for all antibodies.<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_8344\" aria-describedby=\"caption-attachment-8344\" style=\"width: 959px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-8344 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2015\/10\/Figure_42_03_01-959x1024-1.jpg\" alt=\"A two-panel figure describing the genetic basis of antibody diversity. Panel (a) shows the process of V(D)J recombination: a germ-line DNA configuration with multiple V, J, and C gene segments undergoes rearrangement, transcription, and RNA splicing to produce a final mRNA that codes for an antibody light chain. Panel (b) shows the resulting protein structure of a membrane-bound B cell receptor, composed of light and heavy chains with variable and constant regions forming antigen-binding sites.\" width=\"959\" height=\"1024\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2015\/10\/Figure_42_03_01-959x1024-1.jpg 959w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2015\/10\/Figure_42_03_01-959x1024-1-281x300.jpg 281w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2015\/10\/Figure_42_03_01-959x1024-1-768x820.jpg 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2015\/10\/Figure_42_03_01-959x1024-1-65x69.jpg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2015\/10\/Figure_42_03_01-959x1024-1-225x240.jpg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2015\/10\/Figure_42_03_01-959x1024-1-350x374.jpg 350w\" sizes=\"auto, (max-width: 959px) 100vw, 959px\" \/><figcaption id=\"caption-attachment-8344\" class=\"wp-caption-text\">(a) As a germ-line B cell matures, an enzyme called DNA recombinase randomly excises V and J segments from the light chain gene. Splicing at the mRNA level results in further gene rearrangement. As a result, (b) each antibody has a unique variable region capable of binding a different antigen.<\/figcaption><\/figure>\n<p>Similar to TCRs and BCRs, antibody diversity is produced by the mutation and recombination of approximately 300 different gene segments encoding the light and heavy chain variable domains in precursor cells that are destined to become B cells. The variable domains from the heavy and light chains interact to form the binding site through which an antibody can bind a specific epitope on an antigen. The numbers of repeated constant domains in Ig classes are the same for all antibodies corresponding to a specific class. Antibodies are structurally similar to the extracellular component of the BCRs, and B cell maturation to plasma cells can be visualized in simple terms as the cell acquires the ability to secrete the extracellular portion of its BCR in large quantities.<\/p>\n<div id=\"m44823-fig-ch42_03_01\" class=\"figure\" title=\"Figure\u00a042.22.\u00a0\">\n<div class=\"section\" title=\"Antibody Classes\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44823-fs-idm30804944\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Antibody Classes<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44823-fs-idp17788400\"> <\/span>Antibodies can be divided into five classes\u2014IgM, IgG, IgA, IgD, IgE\u2014based on their physiochemical, structural, and immunological properties. IgGs, which make up about 80 percent of all antibodies, have heavy chains that consist of one variable domain and three identical constant domains. IgA and IgD also have three constant domains per heavy chain, whereas IgM and IgE each have four constant domains per heavy chain. The variable domain determines binding specificity and the constant domain of the heavy chain determines the immunological mechanism of action of the corresponding antibody class. It is possible for two antibodies to have the same binding specificities but be in different classes and, therefore, to be involved in different functions.<\/p>\n<p><span id=\"m44823-fs-idm60930656\"> <\/span>After an adaptive defense is produced against a pathogen, typically plasma cells first secrete IgM into the blood. BCRs on na\u00efve B cells are of the IgM class and occasionally IgD class. IgM molecules make up approximately ten percent of all antibodies. Prior to antibody secretion, plasma cells assemble IgM molecules into pentamers (five individual antibodies) linked by a joining (J) chain. The pentamer arrangement means that these macromolecules can bind ten identical antigens. However, IgM molecules released early in the adaptive immune response do not bind to antigens as stably as IgGs, which are one of the possible types of antibodies secreted in large quantities upon re-exposure to the same pathogen.<\/p>\n<figure id=\"attachment_8345\" aria-describedby=\"caption-attachment-8345\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-8345 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_02-1024x556-1.jpg\" alt=\"A table summarizing the five classes of antibodies (immunoglobulins): IgA, IgD, IgE, IgG, and IgM. For each class, the table lists its key properties and functions in the immune system, such as location, role in protection, and special capabilities like crossing the placenta.\" width=\"1024\" height=\"556\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_02-1024x556-1.jpg 1024w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_02-1024x556-1-300x163.jpg 300w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_02-1024x556-1-768x417.jpg 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_02-1024x556-1-65x35.jpg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_02-1024x556-1-225x122.jpg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_02-1024x556-1-350x190.jpg 350w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption id=\"caption-attachment-8345\" class=\"wp-caption-text\">Immunoglobulins have different functions, but all are composed of light and heavy chains that form a Y-shaped structure.<\/figcaption><\/figure>\n<div id=\"m44823-fig-ch42_03_02\" class=\"figure\" title=\"Figure\u00a042.23.\u00a0\">\n<p><span id=\"m44823-fs-idp106928032\"> <\/span>IgAs populate the saliva, tears, breast milk, and mucus secretions of the gastrointestinal, respiratory, and genitourinary tracts. Collectively, these bodily fluids coat and protect the extensive mucosa (4000 square feet in humans). The total number of IgA molecules in these bodily secretions is greater than the number of IgG molecules in the blood serum. A small amount of IgA is also secreted into the serum in monomeric form. Conversely, some IgM is secreted into bodily fluids of the mucosa. Similar to IgM, IgA molecules are secreted as polymeric structures linked with a J chain. However, IgAs are secreted mostly as dimeric molecules, not pentamers.<\/p>\n<p><span id=\"m44823-fs-idm5112096\"> <\/span>IgE is present in the serum in small quantities and is best characterized in its role as an allergy mediator. IgD is also present in small quantities. Similar to IgM, BCRs of the IgD class are found on the surface of na\u00efve B cells. This class supports antigen recognition and maturation of B cells to plasma cells.<\/p>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Antibody Functions\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44823-fs-idp152771184\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Antibody Functions<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44823-fs-idm1203424\"> <\/span>Differentiated plasma cells are crucial players in the humoral response, and the antibodies they secrete are particularly significant against extracellular pathogens and toxins. Antibodies circulate freely and act independently of plasma cells. Antibodies can be transferred from one individual to another to temporarily protect against infectious disease. For instance, a person who has recently produced a successful immune response against a particular disease agent can donate blood to a nonimmune recipient and confer temporary immunity through antibodies in the donor\u2019s blood serum. This phenomenon is called <span id=\"m44823-autoid-cnx2dbk-id1612222\"><\/span><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_8348_8517\"><span id=\"m44823-autoid-cnx2dbk-id1612222\"> <\/span>passive immunity<\/a>; it also occurs naturally during breastfeeding, which makes breastfed infants highly resistant to infections during the first few months of life.<\/p>\n<p><span id=\"m44823-fs-idp52929952\"> <\/span>Antibodies coat extracellular pathogens and neutralize them\u00a0by blocking key sites on the pathogen that enhance their infectivity (such as receptors that \u201cdock\u201d pathogens on host cells). Antibody neutralization can prevent pathogens from entering and infecting host cells, as opposed to the CTL-mediated approach of killing cells that are already infected to prevent progression of an established infection. The neutralized antibody-coated pathogens can then be filtered by the spleen and eliminated in urine or feces.<\/p>\n<figure id=\"attachment_8346\" aria-describedby=\"caption-attachment-8346\" style=\"width: 544px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-8346 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_03.jpg\" alt=\"A three-panel diagram illustrating the mechanisms of antibody action. Panel (a) Neutralization: Antibodies bind to a virus and a toxin, blocking them from attaching to host cells. Panel (b) Opsonization: Antibodies coat a pathogen, marking it for ingestion by a macrophage. Panel (c) Complement Activation: Antibodies bound to a pathogen's surface trigger the complement cascade, forming pores in the pathogen's membrane.\" width=\"544\" height=\"875\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_03.jpg 544w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_03-187x300.jpg 187w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_03-65x105.jpg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_03-225x362.jpg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_03-350x563.jpg 350w\" sizes=\"auto, (max-width: 544px) 100vw, 544px\" \/><figcaption id=\"caption-attachment-8346\" class=\"wp-caption-text\">Antibodies may inhibit infection by (a) preventing the antigen from binding its target, (b) tagging a pathogen for destruction by macrophages or neutrophils, or (c) activating the complement cascade.<\/figcaption><\/figure>\n<div id=\"m44823-fig-ch42_03_03\" class=\"figure\" title=\"Figure\u00a042.24.\u00a0\">\n<p><span id=\"m44823-fs-idm98879504\"> <\/span>Antibodies also mark pathogens for destruction by phagocytic cells, such as macrophages or neutrophils, because phagocytic cells are highly attracted to macromolecules complexed with antibodies. Phagocytic enhancement by antibodies is called opsonization. In a process called complement fixation, IgM and IgG in serum bind to antigens and provide docking sites onto which sequential complement proteins can bind. The combination of antibodies and complement enhances opsonization even further and promotes rapid clearing of pathogens.<\/p>\n<div class=\"section\" title=\"Affinity, Avidity, and Cross Reactivity\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44823-fs-idp128057760\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Affinity, Avidity, and Cross Reactivity<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44823-fs-idp130541824\"> <\/span>Not all antibodies bind with the same strength, specificity, and stability. In fact, antibodies exhibit different <span id=\"m44823-autoid-cnx2dbk-id1634621\"><\/span><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_8348_8518\"><span id=\"m44823-autoid-cnx2dbk-id1634621\"> <\/span>affinities<\/a>\u00a0(attraction) depending on the molecular complementarity between antigen and antibody molecules. An antibody with a higher affinity for a particular antigen would bind more strongly and stably, and thus would be expected to present a more challenging defense against the pathogen corresponding to the specific antigen.<\/p>\n<figure id=\"attachment_8347\" aria-describedby=\"caption-attachment-8347\" style=\"width: 544px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-8347 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_04.jpg\" alt=\"A two-panel diagram explaining antibody binding concepts. Panel (a) contrasts affinity (the strength of a single antigen-binding site interaction, high in IgG) with avidity (the combined strength of all binding sites, high in IgM due to its ten binding sites). Panel (b) illustrates cross-reactivity, where a single antibody can bind to two different, but structurally similar, antigenic epitopes.\" width=\"544\" height=\"892\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_04.jpg 544w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_04-183x300.jpg 183w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_04-65x107.jpg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_04-225x369.jpg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/02\/Figure_42_03_04-350x574.jpg 350w\" sizes=\"auto, (max-width: 544px) 100vw, 544px\" \/><figcaption id=\"caption-attachment-8347\" class=\"wp-caption-text\">(a) Affinity refers to the strength of single interaction between antigen and antibody, while avidity refers to the strength of all interactions combined. (b) An antibody may cross react with different epitopes.<\/figcaption><\/figure>\n<div id=\"m44823-fig-ch42_03_04\" class=\"figure\" title=\"Figure\u00a042.25.\u00a0\">\n<p><span id=\"m44823-fs-idp123736016\"> <\/span>The term <span id=\"m44823-autoid-cnx2dbk-id1299871\"><\/span><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_8348_8519\"><span id=\"m44823-autoid-cnx2dbk-id1299871\"> <\/span>avidity<\/a>\u00a0describes binding by antibody classes that are secreted as joined, multivalent structures (such as IgM and IgA). Although avidity measures the strength of binding, just as affinity does, the avidity is not simply the sum of the affinities of the antibodies in a multimeric structure. The avidity depends on the number of identical binding sites on the antigen being detected, as well as other physical and chemical factors. Typically, multimeric antibodies, such as pentameric IgM, are classified as having lower affinity than monomeric antibodies, but high avidity. Essentially, the fact that multimeric antibodies can bind many antigens simultaneously balances their slightly lower binding strength for each antibody\/antigen interaction.<\/p>\n<p><span id=\"m44823-fs-idp95317264\"> <\/span>Antibodies secreted after binding to one epitope on an antigen may exhibit cross reactivity for the same or similar epitopes on different antigens. Because an epitope corresponds to such a small region (the surface area of about four to six amino acids), it is possible for different macromolecules to exhibit the same molecular identities and orientations over short regions. <span id=\"m44823-autoid-cnx2dbk-id1520463\"><\/span><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_8348_8520\"><span id=\"m44823-autoid-cnx2dbk-id1520463\"> <\/span>Cross reactivity<\/a>\u00a0describes when an antibody binds not to the antigen that elicited its synthesis and secretion, but to a different antigen.<\/p>\n<p><span id=\"m44823-fs-idm96333024\"> <\/span>Cross reactivity can be beneficial if an individual develops immunity to several related pathogens despite having only been exposed to or vaccinated against one of them. For instance, antibody cross reactivity may occur against the similar surface structures of various Gram-negative bacteria. Conversely, antibodies raised against pathogenic molecular components that resemble self molecules may incorrectly mark host cells for destruction and cause autoimmune damage. Patients who develop systemic lupus erythematosus (SLE) commonly exhibit antibodies that react with their own DNA. These antibodies may have been initially raised against the nucleic acid of microorganisms but later cross-reacted with self-antigens. This phenomenon is also called molecular mimicry.<\/p>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Antibodies of the Mucosal Immune System\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44823-fs-idp31880336\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Antibodies of the Mucosal Immune System<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44823-fs-idm58914256\"> <\/span>Antibodies synthesized by the mucosal immune system include IgA and IgM. Activated B cells differentiate into mucosal plasma cells that synthesize and secrete dimeric IgA, and to a lesser extent, pentameric IgM. Secreted IgA is abundant in tears, saliva, breast milk, and in secretions of the gastrointestinal and respiratory tracts. Antibody secretion results in a local humoral response at epithelial surfaces and prevents infection of the mucosa by binding and neutralizing pathogens.<\/p>\n<h2>Review Section<\/h2>\n<p>Antibodies (immunoglobulins) are the molecules secreted from plasma cells that mediate the humoral immune response. There are five antibody classes; an antibody&#8217;s class determines its mechanism of action and production site but does not control its binding specificity. Antibodies bind antigens via variable domains and can either neutralize pathogens or mark them for phagocytosis or activate the complement cascade.<\/p>\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<ol>\n<li>The structure of an antibody is similar to the extracellular component of which receptor?\n<ol>\n<li>MHC I<\/li>\n<li>MHC II<\/li>\n<li>BCR<\/li>\n<li>none of the above<\/li>\n<\/ol>\n<\/li>\n<li><span id=\"m44823-fs-idm96383840\"><span id=\"m44823-fs-idp15569584\">The first antibody class to appear in the serum in response to a newly encountered pathogen is ________.<\/span><\/span>\n<ol>\n<li>IgM<\/li>\n<li>IgA<\/li>\n<li>IgG<\/li>\n<li>IgE<\/li>\n<\/ol>\n<\/li>\n<li><span id=\"m44823-fs-idm117586432\"><span id=\"m44823-fs-idp32974160\">What is the most abundant antibody class detected in the serum upon reexposure to a pathogen or in reaction to a vaccine?<\/span><\/span>\n<ol>\n<li>IgM<\/li>\n<li>IgA<\/li>\n<li>IgG<\/li>\n<li>IgE<\/li>\n<\/ol>\n<\/li>\n<li><span id=\"m44823-fs-idm103783696\"><span id=\"m44823-fs-idp49564592\">Breastfed infants typically are resistant to disease because of ________.<\/span><\/span>\n<ol>\n<li>active immunity<\/li>\n<li>passive immunity<\/li>\n<li>immune tolerance<\/li>\n<li>immune memory<\/li>\n<\/ol>\n<\/li>\n<li><span id=\"m44823-fs-idm59001040\"><span id=\"m44823-fs-idm35976544\">What are the benefits and costs of antibody cross reactivity?<\/span><\/span><\/li>\n<\/ol>\n<p><strong>Answers<\/strong><\/p>\n<ol>\n<li>C<\/li>\n<li>A<\/li>\n<li>C<\/li>\n<li>B<\/li>\n<li>Cross reactivity of antibodies can be beneficial when it allows an individual&#8217;s immune system to respond to an array of similar pathogens after being exposed to just one of them. A potential cost of cross reactivity is an antibody response to parts of the body (self) in addition to the appropriate antigen.<\/li>\n<\/ol>\n<\/div>\n<h1>Adaptation<\/h1>\n<p><span style=\"text-align: initial;font-size: 1em\">This chapter was adapted by Morgan Alford from the following text:<\/span><\/p>\n<p><a href=\"https:\/\/opentextbc.ca\/biology\/part\/chapter-23-the-immune-system\/\">The Immune System<\/a> in <a href=\"https:\/\/opentextbc.ca\/biology\/\">Concepts of Biology, First Canadian Edition<\/a> by Drs. Jane Gair and Charles Molnar is licensed under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">Creative Commons Attribution 4.0 International License<\/a>.<span style=\"font-family: 'Cormorant Garamond', serif;font-size: 2.666667em;text-align: center\">\u00a0<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"media-attributions clear\" prefix:cc=\"http:\/\/creativecommons.org\/ns#\" prefix:dc=\"http:\/\/purl.org\/dc\/terms\/\"><h2>Media Attributions<\/h2><ul><li about=\"https:\/\/opentextbc.ca\/biology\/chapter\/23-3-antibodies\/\"><a rel=\"cc:attributionURL\" href=\"https:\/\/opentextbc.ca\/biology\/chapter\/23-3-antibodies\/\" property=\"dc:title\">Figure_42_03_01-959&#215;1024<\/a>  &copy;  Charles Molnar and Jane Gair    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><li about=\"https:\/\/opentextbc.ca\/biology\/chapter\/23-3-antibodies\/\"><a rel=\"cc:attributionURL\" href=\"https:\/\/opentextbc.ca\/biology\/chapter\/23-3-antibodies\/\" property=\"dc:title\">Figure_42_03_02-1024&#215;556<\/a>  &copy;  Charles Molnar and Jane Gair    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><li about=\"https:\/\/opentextbc.ca\/biology\/chapter\/23-3-antibodies\/\"><a rel=\"cc:attributionURL\" href=\"https:\/\/opentextbc.ca\/biology\/chapter\/23-3-antibodies\/\" property=\"dc:title\">Figure_42_03_03<\/a>  &copy;  Charles Molnar and Jane Gair    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><li about=\"https:\/\/opentextbc.ca\/biology\/chapter\/23-3-antibodies\/\"><a rel=\"cc:attributionURL\" href=\"https:\/\/opentextbc.ca\/biology\/chapter\/23-3-antibodies\/\" property=\"dc:title\">Figure_42_03_04<\/a>  &copy;  Charles Molnar and Jane Gair    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><\/ul><\/div><div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_8348_8516\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_8348_8516\"><div tabindex=\"-1\"><p>protein that is produced by plasma cells after stimulation by an antigen; also known as an immunoglobulin<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_8348_8517\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_8348_8517\"><div tabindex=\"-1\"><p>transfer of antibodies from one individual to another to provide temporary protection against pathogens<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_8348_8518\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_8348_8518\"><div tabindex=\"-1\"><p>attraction of molecular complementarity between antigen and antibody molecules<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_8348_8519\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_8348_8519\"><div tabindex=\"-1\"><p>total binding strength of a multivalent antibody with antigen<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_8348_8520\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_8348_8520\"><div tabindex=\"-1\"><p>binding of an antibody to an epitope corresponding to an antigen that is different from the one the antibody was raised against<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":2418,"menu_order":6,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["c-molnar","j-gair","morganalford"],"pb_section_license":"cc-by"},"chapter-type":[],"contributor":[536,537,535],"license":[52],"class_list":["post-8348","chapter","type-chapter","status-publish","hentry","contributor-c-molnar","contributor-j-gair","contributor-morganalford","license-cc-by"],"part":8316,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters\/8348","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/users\/2418"}],"version-history":[{"count":6,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters\/8348\/revisions"}],"predecessor-version":[{"id":9513,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters\/8348\/revisions\/9513"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/parts\/8316"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters\/8348\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/media?parent=8348"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapter-type?post=8348"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/contributor?post=8348"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/license?post=8348"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}