Thymus is the primary lymphocyte, which is involved the production and maturation of T lymphocytes. T lymphocytes provide cell mediated immunity. B cells, which mature in the bone marrow, are responsible for antibody-mediated immunity. Related Theory Immature T lymphocytes are cells that have not yet encountered their specific antigen. In peripheral lymphoid organs, they can interact with antigen-presenting cells (APCs), which use MHC molecules to present antigen. Once the T lymphocytes recognise their specific antigens, they proliferate and differentiate into one of several effector T lymphocyte subsets. Effector T lymphocytes interact with host cells (rather than the pathogen) to carry out their immune function. T lymphocytes use co-receptors to bind to the MHC molecules. Co-receptors can be either CD4 or CD8. CD proteins help to differentiate major groups of effector T lymphocytes. immature C8+T lymphocytes will become cytotoxic T lymphocytes. Alternatively, CD+T lymphocytes will become T helper lymphocytes, each of which specialised for particular tasks.