from
The Collaborative International Dictionary of English v.0.48
T cell \T" cell`\ (t[=e]"s[e^]l`) [From Thymus, the site of
maturation of T-cells.]
A type of white blood cell that circulates in the blood and
lymph, and provides cell-mediated immunity for the organism,
protecting against infecting cells or the body's own
malignant cells; also called {T lymphocyte}. There are
several types of T cells. They develop, as do B cells, from
progenitor cells in the bone marrow, but are distinguished
from B-cells (B-lymphocytes) by their site of
differentiation; T-cells mature in the thymus and B-cells in
the bone marrow (in birds in the Bursa of Fabricius). They
also have different antigen receptors from those of B-cells.
T-cells differentiate into cells that can directly kill
infecting cells (cell-mediated immunity, cytotoxity) or
activate other cells of the immune system (helper T cells),
whereas B-cells differentiate on activation into
antibody-secreting plasma cells. Helper T cells interact with
B-cells by secreting lymphokines that stimulate the B cell
which have detected a foreign antigen to enter the cell cycle
and develop, by repeated mitosis, into a clone of cells with
identical receptors, and then to secrete antibodies to that
specific antigen.
[PJC]