Image Descriptions

Chapter 1

Figure 1-1A. Surface Barriers

A cross-sectional diagram of skin layers with various components labeled. At the topmost layer, small red shapes are shown representing “Bacterial Pathogen.” Directly beneath the pathogens is the “Skin” layer, depicted in shades of red and pink. Below the skin layer, there are two green circular structures representing “Immune cell (Mast).” These cells are situated above a pale pink area denoting the “Bloodstream,” Which is bordered by pink trapezoidal shapes, representing the endothelial cells that border the bloodstream. The bacterial pathogen, skin, immune cells, and bloodstream are each labeled with black lines pointing to their respective parts. [Return to Figure 1-1A]

Figure 1-1B. Immune Sensing and Communication

A cross-sectional diagram of skin layers showcasing various components. At the top layer, a sharp elongated object is piercing the skin, representing a “Foreign body.” Surrounding the point of entry of the foreign body, there are small red shapes indicating “Bacterial Pathogen.” Below the skin surface, two green circular structures are labeled as “Immune cell (Mast).” Blue structures form radiating arcs from the cells with an arrow through them to represent signalling between the mast cells and the blood vessels. The foreign body, bacterial pathogen, and immune cells are each labeled with black lines pointing to their respective illustrations. [Return to Figure 1-1B]

Figure 1-1C. Inflammation and Fever

A detailed cross-sectional diagram of skin layers displaying various elements. At the top, a sharp object pierces the skin, labeled as a “Foreign body.” Near this point of entry, small red entities signify “Bacterial Pathogen.” Beneath the skin’s surface, there are three distinct types of immune cells. Two large green circles are tagged as “Immune cell (Mast).” Further below, various shaped cells include a blue radiating arcs, denoting cell signaling as well as blue complex shapes labelled “Immune cell (Phagocyte)” and two smaller green circles labelled “Immune cell (Various).” Black lines with annotations point to each element, helping identify the different components in the diagram. [Return to Figure 1-1C]

Figure 1-1D. Phagocytosis

A cross-sectional diagram of skin layers showcases various components. From the top, a “Foreign body,” resembling a sharp object, pierces the skin. Close to this entry point are small red entities representing “Bacterial Pathogen.” Beneath the skin surface, multiple immune cells are depicted: two large green circles labeled “Immune cell (Mast),” blue radiating arcs, denoting cell signalling as well as blue complex shapes labelled “Immune cell (Phagocyte)” and two smaller green circles labelled “Immune cell (Various).” Dotted black arrows extend from the immune cells in the blood vessel into the surrounding tissue, representing the migration of these cells through the process of extravasation. Black lines with annotations point to each element, helping identify the different components in the diagram. [Return to Figure 1-1D]

Figure 1-1E. Adaptive Response

An illustration of a cross-section of skin depicting an immune response. The top layer is labeled “Foreign body,” resembling a sharp object, pierces the skin. Beneath this layer is labeled “Bacterial Pathogen,” showing bacteria entering through the wound. The next layer is labeled “Immune cell (Mast),” with cells depicted alongside antibodies that are interacting with the pathogens. Below this is a label “Antibody,” with antibodies shown binding to antigens on the pathogens. The final layer at the bottom is labeled “Immune cell (Phagocyte),” illustrating phagocyte cells engaging with the pathogens. Arrows indicate ththat phagocytes and antibodies enter the tissues from the bloodstream. [Return to Figure 1-1E]

Chapter 2

Figure 2-1 Mechanical Barriers of the Immune System

A diagram depicts a stylized human figure showing various body parts and their functions related to innate immune defense. On the head, the “Eyelids” are labeled, with a droplet near the eye representing “Tears, Sweat.” The mouth area has a visual representation of a “Cough.” On the right of the diagram, there’s a magnified view of a respiratory tract section. Within this section, “Goblet cells” are depicted as orange oval entities, producing green mucus. Surrounding these goblet cells, hair-like structures called cilia, which are involved in the process of “Mucociliary Clearance.” Below the torso, the “Kidney” is outlined, and further down, the “Urethra” is indicated. Each body part or function is clearly marked with labels. [Return to Figure 2-1]

Figure 2-2 Dysbiosis

The image presents a visual representation of the transition of a host’s microbial environment from healthy to diseased under various conditions. There are three primary sections:

  1. “Healthy host” shows a section of tissue with equal numbers of striped rods, spiked circles and filamentous patches as well as a small number of black oval-shapes, indicating a balanced microbial environment with a suppressed population of opportunistic pathogens.
  2. “Microbial dysbiosis” displays the tissue after being subjected to stressors, resulting in a diminished number of “commensal” striped rods, spiked circles and filamentous patches and a larger number of “opportunistic pathogen” black oval-shapes. There are also a small number of dotted ellipses and spheres, representing “secondary invaders.”
  3. “Diseased host” shows the tissue in a highly compromised state, where the hue of the tissue has been darkened. There are more “opportunistic pathogen” black oval-shapes as well as with the appearance of more pathogenic microbes, including elongated ones and those “secondary invader” dotted ellipses and spheres.

At the bottom of the image, a legend indicates the types of microbes:

  • “Commensal microbes” are represented by striped rods, spiked circles and filamentous patches.
  • “Opportunistic pathogens” are shown as black oval-shapes
  • “Saprophytes/secondary invaders” are depicted by dotted ellipses and spheres.

To the left, there’s a box indicating “Environmental stressors, e.g., ↑Temperature and ↑Pollution” which lead to “Host stress” and reduced “Host defense”, eventually resulting in “Host damage”. This suggests that environmental factors can impact the microbial balance in a host, leading to disease. [Return to Figure 2-2]

Figure 2-3 Hematopoiesis

The image illustrates the differentiation pathway of hematopoietic stem cells into various blood cells. Starting from a “Hematopoietic Stem Cell”, there are two main pathways:

  1. Myeloid Progenitor Pathway:
  • “Red Blood Cell” that delivers oxygen to tissues.
  • “Platelet” that aids in blood clotting and tissue repair.
  • “Mast cell” that initiates the inflammatory response.
  • “Myeloblast” which further differentiates into:
    • “Basophil” which induces inflammation, including asthma.
    • “Eosinophil” which has a role in parasite infection and allergy.
    • “Neutrophil” that consumes pathogens by phagocytosis.
    • “Monocyte” involved in pathogen phagocytosis and antigen presentation to T-Lymphocytes.

The note mentions that within target tissues, monocytes differentiate into more specialized macrophages and dendritic cells.

  1. Lymphoid Progenitor Pathway:
  • “CD4 ‘Helper’ T-Lymphocyte”
  • “CD8 ‘Cytotoxic’ T-Lymphocyte”
  • “B-Lymphocyte”
  • “Natural Killer Cell”

Each cell type is represented with a unique color and shape to distinguish it from others. Lines and arrows indicate the progression and differentiation of cells from their progenitors [Return to Figure 2-3]

Chapter 3

Figure 3-1 Phagocytosis

Diagram depicting the process of phagocytosis in a cell. A Microbial Cell is shown approaching the host cell. The host cell has Pattern Recognition Receptors (PRR) that bind to Pathogen-Associated Molecular Patterns (PAMPs) on the microbial cell’s surface. Upon binding, the process of Phagocytosis begins, with the host cell membrane encircling and encapsulating the microbial cell into a structure labeled ‘Phagosome’. Separate from this, a Lysosome, which contains digestive chemicals and enzymes, is depicted. This lysosome fuses with the phagosome, forming a structure labeled ‘Phagolysosome’. Inside the phagolysosome, the microbial cell undergoes digestion. The final product of this digestion process is then shown being expelled from the host cell, labeled ‘Product of Digestion’. [Return to Figure 3-1]

Figure 3-2 Cytokine Secretion

Diagram illustrating the communication process of immune cells via cytokine proteins. Starting from the left, an Immune cell detects injury or infection, indicated by a large blue cell with the label ‘Immune cell detects injury or infection’. In response, this cell secretes multiple small blue molecules labeled ‘Cytokine Secretion’. These cytokines then bind to a ‘Receptor Protein’ on another cell, sending a ‘Signal’ to that cell. This signal passes into the cell nucleus, represented by a yellow circle, and results in ‘Altered Gene Expression’ within the receiving cell. The outcome of this process is a ‘Biological response’, which can include activation or attraction of another immune cell. Accompanying text explains that the secretion of these cytokines by one cell induces a biological response in another cell and that the specific response is determined by the type and intensity of the secreted cytokine. [Return to Figure 3-2]

Figure 3-3 Cardinal Signs of Inflammation

Sequential illustrations of the stages of skin injury and subsequent signs of inflammation.

  1. A hand showing a site of redness due to ‘Injury’ indicated by a sharp object poking the skin.
  2. The hand depicts ‘Pain’ with jagged red symbols around a wound area.
  3. The hand displays ‘Warmth’ with a red thermometer pointing to the injured area.
  4. The hand shows ‘Swelling’ with a puffed section highlighted.
  5. The hand presents a ‘Scab’ formed over the wound area. Each stage is numerically labeled to indicate the order of events. [Return to Figure 3-3]

Figure 3-3A. Ubiquitous State

A detailed cross-section of the human skin is depicted and labeled “Skin”. The skin’s surface is shown at the top, with a pink gradient indicating depth. Small red rectangles on the skin surface represent “Bacterial Pathogen” attempting to infiltrate. Below, the skin has several layers, each with a unique shade and texture. A green circular cell labeled “Immune cell (Mast)” is seen with numerous internal blue granules labeled “Histamine (in granules)”. These cells are within a faded green region that is above a pick vessel labeled “Bloodstream”. [Return to Figure 3-3A]

Figure 3-3B. Mast cell degranulation

A cross-sectional diagram of human skin depicts the intrusion of a “Foreign body,” illustrated as a jagged red entity piercing the skin’s topmost layer. Beneath the skin’s surface, small red rectangles indicate “Bacterial Pathogen” attempting to penetrate deeper. On the lower left toward the right of the image are green circular cells labeled “Immune cell (Mast)”. Blue circles within these cells are collecting along the lower edge of the circle. The contents of the blue granules are released toward a pink vessel, representing the bloodstream. The chemical signalling between mast cell and the bloodstream is depicted as a series of blue radiating curved lines with an arrow through the center. This chemical signal is labelled “Histamine (vasoactive).” [Return to Figure 3-3B]

Figure 3-3C. Cytokine Signalling

A cross-sectional diagram of human skin depicts the intrusion of a “Foreign body,” illustrated as a jagged red entity piercing the skin’s topmost layer. Small red rectangles within the skin signify harmful pathogens. Two green cells are illustrated with radiating curved blue lines, indicating chemical signalling. Those signals that spread laterally, through the tissue, are labelled “Chemotactic cytokine.” Below these tissues is a pink vessel that is bulging to illustrate the vasodilation of the blood vessel. Within the blood vessel are green circular cells labelled “Immune cell (Various)” as well as blue shapes labeled “Immune cell (Phagocyte).” [Return to Figure 3-3C]

Figure 3-3D. Margination

A cross-sectional diagram of human skin depicts the intrusion of a “Foreign body,” illustrated as a jagged red entity piercing the skin’s topmost layer. Beneath the skin’s surface, small red shapes labeled “Bacterial Pathogen” signify harmful bacterial invaders. Beneath the skin, there is a division between a faded green region, representing the tissues, and a bulging pink vessel that represents the dilated blood vessels. Blue shapes within the tissues illustrate immune cells attracted to the bacteria. Green circles and blue shapes attaching along the inner edge of the blood vessel are labelled “Margination (binds selectin).” [Return to Figure 3-3D]

Figure 3-3E. Tight Adhesion

A cross-sectional diagram of human skin depicts the intrusion of a “Foreign body,” illustrated as a jagged red entity piercing the skin’s topmost layer. Beneath the skin’s surface, small red shapes labeled “Bacterial Pathogen” signify harmful bacterial invaders. Beneath the skin, there is a division between a faded green region, representing the tissues, and a bulging pink vessel that represents the dilated blood vessels. Blue shapes within the tissues illustrate immune cells attracted to the bacteria. Green circles and blue shapes crossing from inner to outer edge of the blood vessel are labelled “Tight adhesion (endothelial ICAM binds leukocyte integrin).” [Return to Figure 3-3E]

Figure 3-3F. Extravasation

A cross-sectional diagram of human skin depicts the intrusion of a “Foreign body,” illustrated as a jagged red entity piercing the skin’s topmost layer. Beneath the skin’s surface, small red shapes labeled “Bacterial Pathogen” signify harmful bacterial invaders. Beneath the skin, there is a division between a faded green region, representing the tissues, and a bulging pink vessel that represents the dilated blood vessels. Green circles and blue shapes represent immune cells that are both in the tissues and along the very outer edge of the blood vessel. Those cells along the outer edge of the blood vessel are labelled “Extravasation (through endothelial pores).” Blue curved lines radiation from many of the cells, illustrating chemical signals that are labelled “Chemotactic and inflammatory cytokines.” [Return to Figure 3-3F]

Figure 3-4 Mechanism of Fever

A two-part image. On the left, a sagittal MRI view of a human head shows the brain and part of the neck. A red arrow points to a specific region in the midbrain, where the hypothalamus is located. On the right, a flowchart describes the process of fever induction. Sequential arrows indicated how ‘Exogenous pyrogens [LPS]’ act on ‘leukocytes’, which then produce ‘endogenous pyrogens IL-1, IL-6, IFN-γ, TNF’. This results in release of ‘PGE2’, which impacts the ‘hypothalamus’ leading to the onset of ‘fever’ highlighted in a red oval. [Return to Figure 3-4]

Figure 3-5 Complement Activation

A diagram depicting the complement system pathways. On the left, the ‘Classical Pathway’ is initiated by an ‘Antibody’ binding to ‘C1q’. This leads to activation of ‘C2’ and ‘C4’. Below it, the ‘Lectin Pathway’ is triggered by ‘Mannose-Binding Lectin (MBL)’, which also converges to activate ‘C2’ and ‘C4’. Both pathways lead to the activation of ‘C3’. In the center, the ‘Alternative Pathway’ is depicted with ‘Factor B’ leading to the activation of ‘C3b’. From ‘C3’, it bifurcates into ‘C3a’, which is associated with ‘Inflammation’, and ‘C3b’. ‘C3b’ further activates ‘C5’, leading to ‘C5a’, also associated with ‘Inflammation’, and ‘C5b’. On the right, ‘C5b’ combines with ‘C6’, ‘C7’, ‘C8’, and ‘C9’ to form the ‘Membrane Attack Complex (MAC)’, which results in ‘Cell Lysis’. [Return to Figure 3-5]

Chapter 4

Figure 4-1 Lymphatic drainage

Illustration depicting the interaction between the circulatory and lymphatic systems. On the left side, a heart is centrally located and is connected to a series of blood vessels. Arrow extending through thick red vessels indicate blood flow through arteries. A network of vessels transitioning from red to blue colour represent a capillary bed. Blue vessels with arrows returning to the heart represent veins. Overlaid on this image of the circulatory system is a diagram of the lymphatic system. Vessels labelled “Lymph Vessels” are arranged alongside the capillaries, with arrows showing fluid flow from blood capillaries into lymph vessels. An arrow shows the conductance of fluid through lymphatic vessels, wherein they pass through structures labelled “Lymph Node”. As lymph vessels converge on the heart a label indicates “Fluid and cells return to bloodstream.” An inset image on the right shows a detailed section of tissue cells with components labeled as “Tissue cells,” “Lymph capillary,” “Arteriole,” “Tissue Fluid,” “Tissue (interstitial) space,” “Venule,” and “Lymphatic vessel.” Arrows and lines guide the viewer in understanding the flow and connections between these structures. [Return to Figure 4-1]

Figure 4-2 Lymphoid organs

Illustration of the human body showcasing the lymphatic system. The figure’s features are labeled as follows: “Adenoid” located near the nasal passage, “Tonsil” at the back of the throat, “Right lymphatic duct, entering vein” in the chest area, “Thymus” in the upper chest, “Spleen” on the left side below the ribs, and “Bone marrow” in the femur of the left leg. Extensive green “Lymph vessels” are shown running throughout the body. On the right side, three detailed insets provide close-up views:

  1. “Thymus” depicted as a lobulated yellow structure.
  2. A detailed view of blood and lymph flow, with labels “Tissue cell,” “Lymphatic vessel,” “Blood capillary,” “Interstitial fluid,” and “Lymphatic capillary” showing the interaction between red blood cells in blood capillaries, green lymph in lymphatic vessels, and the surrounding interstitial fluid.
  3. A “Lymph node” displayed in green with a section showing “Masses of lymphocytes and macrophages.”

Arrows connect the main figure to the detailed insets to indicate their respective positions in the body. [Return to Figure 4-2]

Figure 4-3 Antigen

Illustration of an antigen, depicted as a gray oval shape, with three differently shaped and colored epitopes protruding from its surface. The epitopes are labeled and are in the shapes of a red triangle, a yellow circle, and a green rectangle. Arrows point from the labels “epitopes” and “antigen” to their respective parts in the illustration. [Return to Figure 4-3]

Figure 4-4 Polyclonal Antibodies

Illustration depicting the interaction between antibodies and antigens. The antibodies are represented by Y-shaped structures in green and orange. The antigens are shown as grey structures with various attached shapes: yellow circles, orange triangles, and green squares. Specific sites on the antigens, labeled as “epitope,” are bound by the arms of the “antibody.” The whole grey structure with attached shapes is labeled as “antigen.” [Return to Figure 4-4]

Figure 4-5 Antigen Presentation

  1. Shows an amorphous yellow shape, representing a human antigen presenting cell. Square, circle and triangle shapes on the cell surface are labelled antigen A, B and C, respectively. The cell is interacting with a red circle labeled “T-cell that is specific to Antigen B.” There are three arrows pointing to the T-cell, representing “Antigen A,” “Antigen B,” and “Antigen C.” Above the T-cell is the label “T-cell Activation.”
  2. Depicts a large blue circle labeled “B-cell that is specific to Antigen B.” Surrounding the B-cell are various blue shapes, including triangles and squares, labeled “Cellular Debris.” Only the circular shapes are bound to the B-cell surface.
  3. Illustrates the activation of a B-cell. There are two cells shown: a large red T-cell and a smaller blue B-cell. A grey arrow directed from T-cell to B-cell is labelled “B-cell Activation,” while Y-shaped elements that have separated from the B-cell surface are labelled “Antibody Secretion.” [Return to Figure 4-5]

Figure 4-6 MHC Genetics

On the left, there are two vertically oriented structures. The top one is labeled “Parental Egg” and is colored red with a yellow circle above it. Below it is a similar structure in blue labeled “Parental Sperm” with a rectangle above it. Both structures show segments labeled “Class II” and “Class I.” Under “Class II,” there are parts labeled “DP,” “DQ,” and “DR” with respective numbers. Similarly, under “Class I,” there are parts labeled “B,” “C,” and “A” with respective numbers.

On the right, there’s an outline of a human figure. Adjacent to it, there are two concentric circles. A green circle represents “Most somatic human cells,” and has on its surface HLA-A42, -A24, -B19, -B16, -C3, -C8. A blue circle represents “Antigen Presenting Cells,” and has on its surface HLA-A42, -A24, -B19, -B16, -C3, -C8 as well as HLA-DP35, -DP7, -DQ13, -DQ97, -DR4, -DR33. [Return to Figure 4-6]

Chapter 5

Figure 5-1A Lymphocyte Receptors

Diagram of an antibody structure and its association with the B cell plasma membrane:

The structure consists of two long purple “Heavy chains” and two shorter green “Light chains.” The top ends of these chains form the “Antigen binding site.” These chains are connected by orange “Disulfide bridge” markers. The top portion of the chains is termed the “Variable region,” while the lower portion is the “Constant region.”

The bottom part of the heavy chains extends into the pink “B cell plasma membrane.” Below the membrane, there are two protruding segments labeled “Ig β” and “Ig α,” which represent the “Signal transduction region” of the B cell receptor. [Return to Figure 5-1A]

Figure 5-1B Lymphocyte Receptors

Diagram illustrating the structure of a T-cell receptor (TCR) embedded in a cell membrane:

The TCR consists of two chains, one labeled as the “Alpha chain” in orange and the other as the “Beta chain” in purple. Both chains have two distinct regions: the top part, labeled “Variable region,” and the bottom part, labeled “Constant region.”

These chains extend through the cell membrane, depicted by multiple parallel brown lines representing lipid molecules. The part of the chains embedded in the membrane is labeled “Transmembrane region.” [Return to Figure 5-1B]

Figure 5-2 VDJ Recombination

Diagram illustrating the recombination process of genes in the heavy chain locus for antibody production:

  • “Genes in heavy chain locus”: A sequence of multiple “V” genes (in green), “D” genes (in blue), and “J” genes (in pink) is presented, followed by a single “C” gene (in yellow).
  • “Removal of unwanted D and J gene segment”: The sequence retains multiple “V” genes, but the “D” genes and most “J” genes are crossed out in a red “NO” symbol, leaving only one “J” gene followed by the “C” gene.
  • “Recombination of D and J exons – DJ recombination”: Multiple “V” genes are retained, and a combined “DJ” gene (with “D” in blue and “J” in pink) is shown, followed by the “C” gene.
  • “Removal of unwanted V and D gene segment”: Only two “V” genes are retained, followed by the combined “DJ” gene and the “C” gene. Other “V” and “D” genes are crossed out with a red “NO” symbol.
  • “Recombination of V and DJ exons – VDJ recombination”: A “V” gene is connected to the combined “DJ” gene, indicating the final VDJ recombination, followed by the “C” gene.

At the bottom, it’s stated: “Antibody transcript will also include constant domain gene.” [Return to Figure 5-2]

Figure 5-3 Primary and Secondary Immune Response

Graph depicting the immune response to antigen exposure:

The horizontal axis represents time, marked with intervals of “10 days” and “20 days.” The vertical axis represents “Antibody concentration in serum.”

There are two phases shown:

  1. “Primary Response” after “primary antigen exposure”:
  • A blue curve labeled “IgM” rises and peaks around 14 days and then decreases.
  • A red curve labeled “IgG” begins to rise after the IgM peak, reaching its peak around 20 days and then starts to decrease.
  1. “Secondary Response” after “secondary antigen exposure”:
  • The blue “IgM” curve has a smaller peak around 7 days post-exposure.
  • The red “IgG” curve rises sharply after the IgM peak, reaching a higher concentration than in the primary response and remains elevated, diminishing only slightly after 20 days.

Overall, the graph illustrates the quicker and more potent IgG response upon secondary exposure to an antigen, compared to the primary response. [Return to Figure 5-3]

Figure 5-4 B-Cell Activation

Illustration depicting two cellular interactions in the immune response:

On the left side:

  • A blue “Macrophage” is shown having engulfed red entities labeled “Phagocytosed pathogen.”
  • The macrophage presents an orange structure labeled “MHC class II” that holds a “Peptide antigen.”
  • A green “T helper cell” interacts with the macrophage through its “T cell receptor” binding to the MHC class II and peptide antigen complex.
  • There’s also a blue co-stimulatory ligand on the macrophage labeled “B7” that interacts with a co-stimulatory receptor on the T helper cell labeled “CD28.”

On the right side, separated by a dashed line:

  • A purple “B cell” is shown with a “Foreign pathogen” attached, along with two antibodies: “IgM” and “IgD.”
  • Like the macrophage, the B cell presents an orange “MHC class II” that holds a “Peptide antigen.”
  • The same green “T helper cell” interacts with the B cell in a manner similar to the macrophage: the “T cell receptor” binds to the MHC class II and peptide antigen complex.
  • A co-stimulatory receptor on the B cell labeled “CD40” interacts with a co-stimulatory ligand on the T helper cell labeled “CD40L.”

The illustration highlights the key interactions between immune cells during antigen presentation and co-stimulation. [Return to Figure 5-4]

Figure 5-5 T-Independent B-cell Activation

Diagram illustrating two types of T-cell independent (TI) B cell activation. On the left, ‘TI-1 B Cell Activation’ shows a green B cell interacting with a TI-1 antigen (LPS) via its BCR (IgM) and a PRR (TLR). The BCR and PRR produce signals within the cell, which are illustrated as wavy lines converging on the numbers “1” and “2” and are responsible for the two-step activation of this B-cell. On the right, ‘TI-2 B Cell Activation’ depicts a green B cell interacting with a TI-2 antigen (Polysaccharide). The TI-2 antigen has multiple epitope binding sites, illustrated by red triangles. This causes clustering of multiple B-cell receptors (labeled “BCR (IgM)”) as well as various receptors including C3dg, CD21 (CR2), CD19, and CD81 on one side of the cell. This receptor clustering causes a signal to activate the cell, shown by wavy lines converging on the number “1”. [Return to Figure 5-5]

Figure 5-6 Superantigen

Diagram of an antibody structure and its association with the B cell plasma membrane:

The structure consists of four peptide chains, including two long “Heavy chains” and two shorter “Light chains.” The top end of each chain is green coloured and labelled “Variable Region”. The variable regions collectively form the “Antigen binding site.” The lower portion of each chain is coloured purple and is labeled the “Constant region.” The four chains are connected by orange rectangles, labelled “Disulfide bridge”. The constant region of each heavy chain is embedded in the pink “B cell plasma membrane. Alongside the immunoglobulin are two other peptide chains in red, labeled “Ig β” and “Ig α,” which represent the “Signal transduction region” of the B cell receptor. [Return to Figure 5-6]

Figure 5-6A Effector functions of antibodies

Diagram depicting the agglutination of bacteria by IgM antibodies. Three red blood cells, with surface epitopes, are attached to one another by yellow star-shaped antibody pentamers. Arrows point from two blood cells to the bacteria, labeled ‘bacteria’, and another arrow points from the bacteria to a blood cell, labeled ‘IgM antibody’. Another arrow points from a blood cell to an epitope, labeled ‘epitope’. [Return to Figure 5-6A]

Figure 5-6B Effector functions of antibodies

Diagram illustrating a macrophage engulfing a pathogen because of the antibodies that mark the pathogen for destruction. The yellow macrophage, labeled ‘macrophage’, has green Fc receptors on its surface, pointed out by an arrow labeled ‘Fc receptor’. A brown cell labeled “pathogen” is covered by surface antibodies and those antibodies are anchored to the macrophage by attachment to the Fc receptors. [Return to Figure 5-6B]

Figure 5-6C Effector functions of antibodies

Diagram depicting a virus, diphtheria toxin, and an antibody being neutralized by antibodies. On the left, there’s a gray shape with multiple protrusions labeled ‘virus’, antibodies attach to the surface glycoproteins of the virus that are normally involved in target cell attachment. In the center, a molecule labeled ‘diphtheria toxin’ has two domains, labeled ‘A’ and ‘B’. Antibodies attach to the B-domain,rendering the toxin harmless.On the right, an elongated tan-colored structure represents a bacterial cell with antibodies attached to a red line, corresponding to the bacterial flagellum. [Return to Figure 5-6C]

Figure 5-6D Effector functions of antibodies

Diagram illustrating the interaction between an NK cell, IgG antibody, and a pathogen. On the left side, a purple NK cell labeled ‘NK cell’ has protrusions called ‘Fc receptor’. Below it, an elongated tan structure represents a pathogen labeled ‘pathogen’, which has an antigen on its surface labeled ‘antigen’. Interacting with the antigen is a structure labeled ‘IgG antibody’. An arrow in the middle points to the right side, where the NK cell Fc receptors are shown anchored with the antibodies and the NK cell is releasing green particles labeled ‘cytotoxins’ towards the pathogen, indicating an immune response. [Return to Figure 5-6D]

Figure 5-7 Characteristics of different immunoglobulin classes

Table titled ‘The Five Immunoglobulin (Ig) Classes’ detailing the properties of various classes of immunoglobulins. The table has columns for IgG monomer, IgM pentamer, Secretory IgA dimer, IgD monomer, and IgE monomer. Properties listed are:

  • ‘Structure’: Depictions of each immunoglobulin with unique shapes.
  • ‘Heavy chains’: Values are ‘γ’ for IgG, ‘μ’ for IgM, ‘α’ for Secretory IgA, ‘δ’ for IgD, and ‘ε’ for IgE.
  • ‘Number of antigen-binding sites’: IgG has 2, IgM has 10, Secretory IgA has 4, and both IgD and IgE have 2.
  • ‘Molecular weight (Daltons)’: IgG is 150,000, IgM is 900,000, Secretory IgA is 385,000, IgD is 180,000, and IgE is 200,000.
  • ‘Percentage of total antibody in serum’: IgG is 80%, IgM is 6%, Secretory IgA is 13% (monomer), and both IgD and IgE are <1%.
  • ‘Crosses placenta’: Only IgG has ‘yes’, while others are ‘no’.
  • ‘Fixes complement’: IgG and IgM have ‘yes’, while others are ‘no’.
  • ‘Fc binds to’: IgG binds to ‘phagocytes’, and IgE binds to ‘mast cells and basophils’.
  • ‘Function’: IgG is responsible for ‘Neutralization, agglutination, complement activation, opsonization, and antibody-dependent cell-mediated cytotoxicity’. IgM performs ‘Neutralization, agglutination, and complement activation’, and its monomer form is also the ‘B-cell receptor’. Secretory IgA handles ‘Neutralization and trapping of pathogens in mucus’. IgD acts as a ‘B-cell receptor’, and IgE is involved in the ‘Activation of basophils and mast cells against parasites and allergens’. [Return to Figure 5-7]

Figure 5-8 Effector function of cytotoxic T-cell

Diagram illustrating the interaction and activation process of a T cell during an immune response. On the left, a ‘naive CTL’ (Cytotoxic T Lymphocyte) is shown with labels for ‘CD8’ and ‘TCR’ (T cell receptor). Beneath, there’s an ‘infected cell’ containing an ‘intracellular pathogen’ and a surface marker ‘MHC I’ (Major Histocompatibility Complex class I). A close-up interaction between the naive CTL and the infected cell is depicted in the center. Here, the infected cell has ‘antigen extracted from pathogen’, which is displayed on the clel surface by ‘MHC class I.’

‘T cell receptor’ and ‘CD8’ on the CTL recognize and bind to the ‘MHC class I’ on the infected cell. As a result, the CTL becomes an ‘activated CTL’. On the right, the ‘activated CTL’ releases ‘granzymes’ and ‘perforins’, which leads to the ‘controlled destruction of infected cell through apoptosis’. [Return to Figure 5-8]

Chapter 6

Figure 6-1 Herd Immunity

A diagram illustrating the spread of a contagious disease in a population based on immunization levels. The figures are represented in three colors: Blue (not immunized, but still healthy), Yellow (immunized and healthy), and Red (not immunized, sick, and contagious).

  1. The first section shows a group of entirely blue figures with the label “No one is immunized.” A circle highlights a few blue figures turning red with the text “Contagious disease spreads through the population.”
  2. In the second section, the group consists of both blue and a few yellow figures. The label reads “Some of the population gets immunized.” A circle highlights a mix of blue figures turning red and yellow figures unaffected, with the text “Contagious disease spreads through some of the population.”
  3. The third section presents a majority of yellow figures with a few blue ones. It’s labeled “Most of the population gets immunized.” A circle highlights only a few blue figures turning red, demonstrating that the disease’s spread is limited. The accompanying text reads, “Spread of contagious disease is contained.” [Return to Figure 6-1]

Chapter 7

Figure 7-1 Allergy Sensitization and Provocation

Step-by-step depiction of the allergic response mechanism in the immune system:

  1. An “antigen-presenting cell” (APC) is shown processing an “antigen” (depicted as a wavy blue line). The caption reads, “Upon first exposure to allergen, APC processes antigen and presents it to Th2 cell.” The antigen is presented to a “Th2 cell” using a structure labeled “class II MHC.”
  2. A Th2 cell releases molecules labeled “IL-4,” targeting a “B cell.” The caption specifies, “Th2 cell releases IL-4 and IL-12, which activate B cell.”
  3. The activated B cells multiply and differentiate into “plasma cells” shown producing “IgE antibodies.” The description states, “B cells proliferate and differentiate into plasma cells that synthesize and secrete IgE antibody.”
  4. The produced IgE antibodies bind to “mast cells,” particularly at a region labeled “Fc region,” sensitizing them. The corresponding caption reads, “IgE binds to mast cells by Fc region, sensitizing the mast cells.”
  5. When there is a subsequent exposure to the allergen, the sensitized mast cells with IgE bind to the antigen, leading to the release of “inflammatory molecules”. The caption describes, “Upon subsequent exposure to allergen, mast cells with IgE bind to antigen and release inflammatory molecules, resulting in allergy symptoms.”

Throughout, arrows guide the viewer’s eyes to follow the sequence of events, emphasizing the interaction and progression of the allergic response. [Return to Figure 7-1]

Figure 7-2 Allergy Therapy

Representation of the allergic response and its management through various interventions:

  1. The silhouette of a human face and upper torso is depicted, with orange allergen particles entering the nasal passage. This stage is labeled “Allergen.”
  2. To the right of the figure, a “Plasma B-cell” produces an “IgE” antibody, symbolized by a yellow oval. The sequence is numbered “2.”
  3. This IgE antibody binds to a “Mast cell,” shown as a larger circle with smaller circles inside, labeled “3.”
  4. Upon allergen binding, the mast cell undergoes “degranulation,” releasing particles, leading to symptoms illustrated on the left: “Sneezing,” “Runny nose,” “Tearing,” “Rash,” “Edema,” and “Itching.” This stage is labeled “4.”

Interventions to counteract this allergic response are detailed on the right:

  • “Corticosteroids (e.g., hydrocortisone)” are shown with a line pointing towards the Plasma B-cell, described as inhibiting “T-cell activation and IgE synthesis.”
  • “Anti-IgE (e.g., omalizumab)” is pointed towards the IgE antibody, mentioned as eliminating these antibodies before they can contact the mast cell.
  • Below the mast cell, “Cromolyn” is depicted as inhibiting mast cell degranulation.

At the bottom, additional interventions include:

  • “Antihistamines” that counteract the effects of mast cell histamine release.
  • “Non-steroidal anti-inflammatory drugs (NSAIDs, e.g., aspirin)” are said to counteract cytokines that induce general inflammation.

The entire process is depicted using arrows, guiding the viewer through the stages and interventions in managing allergic reactions. [Return to Figure 7-2]


Figure A1-1-1 Blood Groups

Table detailing the characteristics of different blood types: A, B, AB, and O. The table is divided into rows and columns, with each row representing a specific characteristic and each column corresponding to a blood type.

  1. “Red blood cell type” row:
  • Blood type A: A red blood cell illustrated with an “A” in its center and surrounded by small purple antigens.
  • Blood type B: A red blood cell illustrated with a “B” in its center and surrounded by small teal antigens.
  • Blood type AB: A red blood cell illustrated with “AB” in its center, surrounded by both small purple and teal antigens.
  • Blood type O: A plain red blood cell without any surrounding antigens.
  1. “Isohemagglutinins” row:
  • Blood type A: Represents “Anti-B” isohemagglutinins with five teal Y-shaped structures that form the ring that is characteristic of immunoglobulin-M (IgM).
  • Blood type B: Represents “Anti-A” isohemagglutinins with purple IgM structures.
  • Blood type AB: The label “None,” indicating no isohemagglutinins.
  • Blood type O: Represents both “Anti-A and Anti-B” isohemagglutinins with a combination of purple and teal IgM structures.
  1. “Antigens on red blood cell” row:
  • Blood type A: A small purple circle representing the “A antigen.”
  • Blood type B: A small teal diamond representing the “B antigen.”
  • Blood type AB: Both a small purple circle and a teal diamond, representing “A and B antigens.”
  • Blood type O: The label “None,” indicating no antigens.

This table provides a visual summary of the cellular characteristics and antibodies associated with each blood type.

Figure A1-1-2 ABO Blood Typing (Top)


Figure A1-1-2 ABO Blood Typing (Bottom)


Figure A1-2-1 The Coombs test

The illustration depicts the processes of the Direct Coombs test and the Indirect Coombs test, both methods used to detect certain types of antibodies associated with immune responses.

Direct Coombs test / Direct antiglobulin test: 

  1. A depiction of a blood sample being taken from a patient’s arm, with the note: “Blood sample from a patient with immune mediated haemolytic anaemia: antibodies are shown attached to antigens on the RBC surface.”
  2. A tube with red blood cells (RBCs) is washed, and the washed RBCs are then incubated with antihuman antibodies (Coombs reagent) represented by blue Y-shaped structures.
  3. The result is shown with RBCs agglutinated or clumped together, with a note: “RBCs agglutinate: antihuman antibodies form links between RBCs by binding to the human antibodies on the RBCs.” A label states “Positive test result” next to a test tube showing the clumped RBCs.

Indirect Coombs test / Indirect antiglobulin test: 

  1. A recipient’s serum containing antibodies (Ig’s) is depicted in a test tube.
  2. A separate tube shows a donor’s blood sample added to the tube with the recipient’s serum.
  3. The mixture shows the recipient’s Ig’s that target the donor’s red blood cells, forming antibody-antigen complexes.
  4. Anti-human Ig’s (Coombs antibodies) are added to the solution, depicted as blue Y-shaped structures.
  5. The result shows agglutination of red blood cells due to human Ig’s attached to the RBCs. A label says “Positive test result” next to a tube showing the clumped RBCs.

A Legend is provided on the right:

  • Red blobs represent “Antigens on the red blood cell’s surface.”
  • Grey Y-shaped structures indicate “Human anti-RBC antibody.”
  • Blue Y-shaped structures represent “Antihuman antibody (Coombs reagent).”

This illustration provides a step-by-step visual summary of how both the Direct and Indirect Coombs tests are conducted and their positive results.

Figure A1-3-1: TPHA assay performed in a microwell plate


A1-4-1 Tube agglutination test for diagnosing typhoid fever

  1. “Serial dilution” is shown at the top. Six test tubes in a row, each containing a yellow liquid (serum), are displayed. A red arrow pointing downwards is labeled “Add serum,” indicating that serum is added to the first tube. The tubes are labeled with increasing dilution ratios from left to right: “1:20,” “1:40,” “1:80,” “1:320,” and “1:640.” These ratios represent “Serum : Normal saline.” An upward-pointing red arrow on the rightmost tube is labeled “discard,” indicating the removal of excess serum.
  2. “Add antigens” is displayed below the test tubes. A list of antigens to be added to a plate is provided: “S. Typhi – O Ag,” “S. Typhi – H Ag,” “S. Paratyphi A – H Ag,” “S. Paratyphi B – H Ag,” and “S. Paratyphi C – H Ag.” Adjacent to this list, a rectangular plate with multiple wells is shown. Red arrows point from each antigen on the list to the rows of wells in the plate, indicating where each antigen should be added.
  3. The next instruction reads: “Mix properly, cover and incubate at 37° C overnight.”
  4. The final step is labeled: “Observe for agglutination and interpret the results.”

The entire process provides a step-by-step visual guide to preparing serum samples, adding antigens, incubating, and observing for reactions.

Figure A2-1-1 Hybridoma technology

Step-by-step visualization of a laboratory procedure involving mice and cellular components:

  1. Yellow triangles, possibly representing specific proteins or molecules, are being injected into a mouse using a syringe.
  2. A mouse has cellular structures, indicating B-cells with blue , red and yellow Y-shaped surface structures, indicating antibodies that are specific to different antigens. A syringe is illustrated extracting these B-cells from the spleen of the mouse.
  3. A bone is depicted, with a magnified section showing blue cellular structures, representing mouse myeloma cells. These  cells are being extracted from the bone section using a syringe.
  4. An isolated view of both blue myeloma cells and B-cells with surface antibodies. A converging line represents the fusion of these cells to form hybridoma cells that are blue myeloma cells with surface antibodies.
  5. Three hybridoma cells are shown with arrows to petri plates, indicating that these cells are cultured in these plates.
  6. (a) A magnifying glass closely examines a dish with the cellular structures, showing the details of their molecular components. (b) The same magnifying process, but an unwanted cell is identified and is shown being discarded into a waste bin, symbolizing the removal of undesired cells.
  7. Hybridoma cells are illustrated (a) growing in petri plates or (b) being injected into a mouse. Both of these processes are methods to greatly amplify the number of hybridoma cells.
  8. The final image showcases an abundance of yellow Y-shaped structures, indicating a successful production of large quantities of antibodies.

This graphic provides a visual representation of a research method involving manufacture of antibodies from hybridoma cell lines.

Figure A3-1-1 CH50 assay


Figure A3-2-1 AH50 assay


Figure A4-1 The complement fixation assay


A5-1 Common ELISA assays

Four different types of enzyme-linked immunosorbent assay (ELISA) methods:

  1. “Direct ELISA” displays an antigen labeled “Ag” at the bottom, linked to a “Primary antibody conjugate” represented by an orange Y-shaped structure. Above this antibody is a green circle labeled “Substrate,” and a blue starburst shape representing the reaction.
  2. “Indirect ELISA” shows the same antigen “Ag” at the bottom, linked to the orange Y-shaped structure. Above this is a green Y-shaped “Secondary antibody conjugate.” At the top, there’s the green “Substrate” circle and the blue starburst shape.
  3. “Sandwich ELISA” features a purple Y-shaped “Capture antibody” at the bottom, holding a blue circular antigen. Above the antigen is a yellow Y-shaped detection antibody, which is further attached to the green Y-shaped “Secondary antibody conjugate,” followed by the green “Substrate” circle and the blue starburst shape.
  4. “Competitive ELISA” displays the orange Y-shaped antibody attached to a smaller blue circle. To its left is a second Y-shaped antibody attached to a red circle labeled “Inhibitor antigen.” Above the antibody and inhibitor antigen, there’s the green “Substrate” circle and the blue starburst shape.

Each method represents a specific configuration of antibodies, antigens, and substrates to detect the presence or quantity of a target substance.

Figure A6-1 The T.SPOT TB assay



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Basic Concepts in Applied Immunology Copyright © 2023 by Simon Duffy and Supipi Duffy is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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