GENERATION OF T AND B

CELL DIVERSITY43.2• Immunoglobulin (Ig) gene that encodes the light

chain of both secreted antibodies and membrane-bound B cell antigen receptors.

• A receptor light chain is encoded by three gene segments: a variable (V) segment, a joining ( J) segment, and a constant (C) segment.

Immunoglobulin (antibody) gene rearrangement

ORIGIN OF SELF-TOLERANCE

How does adaptive immunity distinguish self from nonself

• Because antigen receptor genes are randomly rearranged, some immature lymphocytes produce receptors specific for epitopes on the organism’s own molecules.

• Some B and T cells with receptors specific for the body’s own molecules are destroyed by apoptosis, which is a programmed cell death.

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PROLIFERATION OF B CELLS AND T CELLS

How is adaptive immunity so effective

• An antigen is presented to a steady stream of lymphocytes in the lymph nodes until a match is made. A successful match then triggers changes in cell number and activity for the lymphocyte to which an antigen has bound.

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CLONAL SELECTION

IMMUNOLOGICAL MEMORY

Thucydides observed that individuals who had recovered from the plague could safely care for those who were sick or dying, “for the same man was never attacked twice—never at Least fatally.”

THE SPECIFICITY OF IMMUNOLOGICAL MEMORY