lymphocyte T-lymphocyte 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. BTO:0000782 BrendaTissueOBO T cell T lymphocyte T-cell