1. • 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.
3. 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.
4. 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.
6. 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.”
