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Figure

(a) 1. After digesting antigen-bearing agents, a macrophage displays antigens on its surface. 2. Helper T cells become activated when they contact displayed antigens that fit their antigen receptors. 3. An activated helper T cell interacts with a B cell that has combined with an identical antigen and causes the B cell to proliferate. (b) Macrophages bind to lymphocytes. During an infection, macrophages bind to helper T cells, activating them to trigger other immune defenses. Here, the round cells are helper T cells and the cells bearing projections are macrophages (1,040x).

Macrophage

Helper T cell

Shier Butler And Lewis Body Parts

Shier-Butler-Lewis: IV. Transport 16. Lymphatic System and © The McGraw-Hill

Human Anatomy and Immunity Companies, 2001

Physiology, Ninth Edition the proliferation. The daughter cells of the stimulated B cell mature into either plasma cells or memory cells. Plasma cells produce and secrete large globular proteins called antibodies, which are also called immunoglobulins (im"u-no-glob'u-linz). A plasma cell is an antibody factory, as evidenced by its characteristically huge Golgi apparatus. At the peak of an infection, a plasma cell may produce and secrete 2,000 antibody molecules a second! Body fluids carry antibodies, which then react in various ways to destroy specific antigens or antigen-bearing particles. This antibody-mediated immune response is called humoral immunity ("humoral" refers to fluid).

B Cell Activation

When an activated helper T cell encounters a B cell that has already combined with an identical foreign antigen, the helper cell releases certain cytokines. These cy-tokines stimulate the B cell to proliferate, thus enlarging its clone of antibody-producing cells (figs. 16.18 and 16.19). T cells can also suppress antibody formation by releasing cytokines that inhibit B cell function.

Some members of the activated B cell's clone differentiate further into plasma cells, which secrete antibodies similar in structure to the antigen-receptor molecules on the original B cell's surface. These antibodies can combine with the antigen-bearing agent that has invaded the body, and react against it. Table 16.5 summarizes the steps leading to antibody production as a result of B and T cell activities.

A single type of B cell carries information to produce a single type of antibody. However, different B cells respond to different antigens on a pathogen's surface. Therefore, an

Stimulation by activated helper T cell

Cloning Helper Cell

Stimulation by activated helper T cell

Clone of B cells

Figure

When a B cell encounters an antigen that fits its antigen receptor, it becomes activated and proliferates, thus enlarging its clone. Note that all cells in the clone have the same antigen receptor.

Clone of B cells

Figure

When a B cell encounters an antigen that fits its antigen receptor, it becomes activated and proliferates, thus enlarging its clone. Note that all cells in the clone have the same antigen receptor.

Shier-Butler-Lewis: IV. Transport 16. Lymphatic System and © The McGraw-Hill

Human Anatomy and Immunity Companies, 2001

Physiology, Ninth Edition

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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