Human lymphocyte (phase-contrast microphotograph).
Type of
leukocyte fundamental to the
immune system, regulating and participating in acquired
immunity. Each has receptor molecules on its surface that bind to a specific
antigen. The two primary types,
B cells and
T cells, originate from stem cells in
bone marrow and travel to
lymphoid tissues. When a B cell binds to an antigen, it multiplies to form a clone of identical cells. Some of these, acted on by helper T cells, differentiate into plasma cells that produce
antibodies against the antigen. Others (memory cells) multiply, providing long-term
immunity to the antigen.
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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
