Adaptive immunity depends on T and B lymphocytes produced in the bone marrow. T lymphocytes mature in the thymus gland. The thymus is highly active through adolescence and atrophies in adults. T lymphocytes become cytotoxic or promote B cell differentiation. B lymphocytes mature in red bone marrow. B lymphocytes are precursors of antibody-producing plasma cells. All lymphocytes take up residence in peripheral lymphoid tissues and circulate in the bloodstream. The response of the adaptive immune system can be humoral (antibody-mediated) or cell-mediated (dependent on cellular responses).
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