Functions of Cells and Molecules Involved in Immunity

Question 1

B cell

Answer 1

Lymphocyte that resides in the lymph nodes, spleen, or other lymphoid tissues, where it is induced to replicate by antigen-binding and helper T cell interactions; its progeny (clone members) form plasma cells and memory cells

Question 2

Plasma cell

Answer 2

Antibody-producing “machine”; produces huge numbers of the same antibody (immunoglobulin); specialized B cell clone descendant

Question 3

Helper T cell

Answer 3

A T cell that binds with a specific antigen presented by an APC; it stimulates the production of other immune cells (cytotoxic T cells and B cells) to help fight the invader; acts both directly and indirectly by releasing cytokines

Question 4

Cytotoxic T cell

Answer 4

Activity enhanced by helper T cells; its specialty is killing virus-invaded body cells, as well as body cells that have become cancerous; involved in graft rejection

Question 5

Regulatory T cell

Answer 5

Slows or stops the activity of B and T cells once the infection (or attack by foreign cells) has been conquered. Thought to be important in preventing autoimmune diseases

Question 6

Memory cell

Answer 6

Descendant of an activated B cell or T cell; generated during both primary and secondary immune responses; may exist in the body for years thereafter, enabling it to respond quickly and efficiently to subsequent infections or meetings with the same antigen

Question 7

Antigen-presenting cell (APC)

Answer 7

Any of several cell types (macrophage, dendritic cell, B cell) that engulfs and digests antigens that it encounters and presents parts of them on its plasma membrane for recognition by T cells bearing receptors for the same antigen; this function, antigen presentation, is essential for normal cell-mediated responses. Macrophages and dendritic cells also release chemicals (cytokines) that activate many other immune cells

Question 8

Antibody (immunoglobulin)

Answer 8

Protein produced by a B cell or its plasma-cell offspring and released into body fluids (blood, lymph, saliva, mucus, etc.), where it attaches to antigens, causing neutralization, opsonization, precipitation, or agglutination, which “marks” the antigens for destruction by phagocytes or complement

Question 9

Cytokines

Answer 9

Chemicals released by sensitized T cells, macrophages, and certain other cells:
• Migration inhibiting factor (MIF)—”inhibits” macrophage migration and keeps them in the local area.
• Interleukin 2—stimulates T cells and B cells to proliferate; activates NK cells.
• Helper factors—enhance antibody formation by plasma cells
• Suppressor factors—suppress antibody formation or T cell–mediated immune responses (interleukin-10 transforming growth factor and others)
• Chemotactic factors—attract leukocytes (neutrophils, eosinophils, and basophils) into inflamed area
• Gamma interferon—secreted by lymphocytes; helps make tissue cells resistant to viral infection; activates macrophages and NK cells; enhances maturation of cytotoxic T cells

Question 10

Tumor necrosis factor (TNF)

Answer 10

Like perforin, causes cell killing; attracts granulocytes; activates T cells and macrophages

Question 11

Complement

Answer 11

Group of bloodborne proteins activated after binding to antibody-covered antigens; when activated, complement causes lysis of the microorganism and enhances inflammatory response

Question 12

Antigen

Answer 12

Substance capable of provoking an immune response; typically a large, complex molecule not normally present in the body

Question 13

Cytotoxins

Answer 13

Perforin, granzymes—cell toxins released by cytotoxic T cells and NK cells