Model for studying the effects of TNF on T-cell differentiation and maturation. T cells are stimulated with cognate antigen in the presence of irradiated antigen-presenting cells for periods of up to 14 days in the presence or absence of recombinant TNF. Cytokines are added to cultures every 2 or 3 days. At the end of the culture period, T cells are washed extensively and then rechallenged with specific antigen or anti-CD3 mAb in the absence of TNF. APC, antigen-presenting cell; T, T cell; TNF, tumour necrosis factor-α.