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Definition of LYMPHOCYTE
: any of the colorless weakly motile cells originating from stem cells and differentiating in lymphoid tissue (as of the thymus or bone marrow) that are the typical cellular elements of lymph, include the cellular mediators of immunity, and constitute 20 to 30 percent of the white blood cells of normal human blood — compare b cell, t cell
: any of the colorless weakly motile cells that originate from stem cells and differentiate in lymphoid tissue (as of the thymus or bone marrow), that are the typical cellular elements of lymph, that include the cellular mediators of immunity, and that constitute 20 to 30 percent of the white blood cells of normal human blood—see b cell, t cell
Human lymphocyte (phase-contrast microphotograph).—Manfred Kage/Peter Arnold
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.