noun
Usage: usually capitalized T
Etymology: t hymus-derived cell
: any of several lymphocytes (as a helper T cell) that differentiate in the thymus, possess highly specific cell-surface antigen receptors, and include some that control the initiation or suppression of cell-mediated and humoral immunity (as by the regulation of T and B cell maturation and proliferation) and others that lyse antigen-bearing cells — called also T lymphocyte — see helper t cell herein cytotoxic t cell herein suppressor t cell herein t4 cell herein