Chap 43

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The five classes of immunoglobulins. Immunoglobulins (antibodies) recognize "foreign" particles. All classes consist of Y–shaped molecules in which the tail region is distinct for each class. IgM and IgA antibodies contain a J chain that helps hold the monomeric subunits together.

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An overview of the acquired immune response.

Once activated, a helper T cell stimulates the humoral response by contacting B cells. An activated helper T cell stimulates the cell–mediated response indirectly via cytokines.

An overview of the acquired immune response.
Once activated, a helper T cell stimulates the humoral response by contacting B cells.		An activated helper T cell stimulates the cell–mediated response indirectly via cytokines.

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Mast cells, IgE, and the allergic response.

Long-term effects of fire on a tallgrass prairie community in Kansas.

IgE antibodies produced in response to initial exposure to an allergen bind to receptors or mast cells. On subsequent exposure to the same allergen, IgE molecules attached to a mast cell recognize and bind the allergen. Degranulation of the cell, triggered by cross-linking of adjacent IgE molecules, releases histamines, leading to allergy symptoms.

Long-term effects of fire on a tallgrass prairie community in Kansas.
IgE antibodies produced in response to initial exposure to an allergen bind to receptors or mast cells.		On subsequent exposure to the same allergen, IgE molecules attached to a mast cell recognize and bind the allergen.		Degranulation of the cell, triggered by cross-linking of adjacent IgE molecules, releases histamines, leading to allergy symptoms.

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Antibody-mediated mechanisms of antigen disposal. Following activation of the complement system, the membrane attack complex (MAC) forms pores in foreign cells. The pores allow ions and water to rush into the cell, leading to its swelling and eventual lysis.

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Antigen receptors on lymphocytes. All the antigen receptors on a B cell or T cell bind the same antigen. The variable (V) regions vary extensively from cell to cell, the constant (C) regions vary little or not at all.

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Clonal selection of B cells.

A B cell is selected by an antigen to proliferate and differentiate into long-lived memory cells and antibody–secreting short-lived plasma cells.

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The killing action of cytotoxic T cells. After interacting with a target cell (such as a cancer cell), an activated cytotoxic T cell releases perforins and proteolytic enzymes (granzymes) that promote death of the target cell.

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External innate defense by mucous membranes.
The lining of the trachea contains mucus–producing cells (orange) and cells with cilia (yellow). Synchronized beating of the cilia expels mucus and trapped microbes upward into the pharynx.

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Epitopes (antigenic determinants).
Small, specific regions on antigens, called epitopes, are bound by the antigen receptors on lymphocytes and by secreted antibodies.

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The central role of helper T cells. The SEM of a dendritic cell reveals its long branching extensions, reminiscent of the dendrites of a nerve cell. Dendritic cells are the primry antigen–presenting cells during the primary response to an antigen.

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A T cell infected with HIV. Newly made virus particles (gray) are seen budding from the surface of a T cell.

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Humoral immune response. The TEM of a plasma cell reveals abundant endoplasmic reticulum, a common feature of cells dedicated to making proteins for secretion.

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Acquired immunity.
The defenses provided by acquired immunity against specific pathogens develop more slowly.

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Innate immunity.
If an invading pathogen breaches the body's external innate defenses, various internal innate defenses quickly come into play.

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Major events in the local inflammatory response.

Chemical signals released macrophages cause nearby capillaries to widen and become more permeable. Clotting elements move from the blood to the site. Clotting begins.

Major events in the local inflammatory response.
Chemical signals released macrophages cause nearby capillaries to widen and become more permeable.		Clotting elements move from the blood to the site. Clotting begins.

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Chemokines released by various kinds of cells attract phagocytes from the blood. Neutrophils and macrophages phagocytose pathogens.

Chemokines released by various kinds of cells attract phagocytes from the blood.		Neutrophils and macrophages phagocytose pathogens.

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The lymphatic system traps foreign particles.

The lymphatic system returns fluid to the circulatory system.

Microbes that invade interstitial fluid are trapped in connective tissue of lymph nodes, where they are attacked by macrophages and lymphocytes.

Microbes that enter the blood become trapped in the spleen, where they encounter macrophages.

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Lymphocyte development.
Lymphocytes differentiate from stem cells: B cells develop entirely in the bone marrow; T cells complete their development in the thymus.

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A macrophage ingesting a yeast cell.
White blood cells such as macrophages and neutrophils can ingest foreign pathgens.

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The specificity of immunological memory. Memory cells generated in the primary response to antigen A give rise to a heightened secondary response to the same antigen, but do not affect the primary response to a different antigen.

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The T cell receptor binds with an MHC molecule–peptide antigen complex.

Class I MHC molecules are made by most nucleated cells. Class II MHC molecules are made by antigen–presenting cells (macrophages, dendritic cells, and B cells).

The T cell receptor binds with an MHC molecule–peptide antigen complex.
Class I MHC molecules are made by most nucleated cells.		Class II MHC molecules are made by antigen–presenting cells (macrophages, dendritic cells, and B cells).

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Phagocytosis.

A macrophage engulfs microbes by t_cells.html: 43_09TcellsAndMHC_A.jpg

The interaction of T cells with MHC molecules. Class I and class II MHC molecules display peptide fragments of antigens to cytotoxic T cells and helper T cells, respectively. In each case, the T cell receptor binds with an MHC molecule–peptide antigen complex. Class I MHC molecules are made by most nucleated cells, whereas class II MHC molecules are made primarily by antigen–presenting cells (macrophages, dendritic cells, and B cells).