This process is called clonal expansion and is antigen driven. B lymphocytes produce antibodies and some soluble mediators called cytokines. They arise in the bone marrow in adult mammals. T lymphocytes arise in bone marrow but mature in the thymus. They do not produce antibody molecules but have surface receptors structurally related to Ig.
T cells see antigen in a different way to B cells.
They recognise peptide fragments of antigen complexed with cell surface MHC glycoproteins on neighbouring cells. There are two sub-types of T cell defined on the basis of function, accessory molecule expression and the type of MHC protein presenting antigen to them. NK cells represent a first line of defence to infections, tumour growth and other pathogenic alterations of tissue homoeostasis. NK cells do not express antibodies or T cell receptors at their cell surface. They produce cytokines and express receptors for immunoglobulin.