CA2-CELLS INDUCED BY STIMULATION OF CD4 OR CD8 AND INTERFERENCE WITH CD3 STIMULATION( RESPONSE IN SINGLE HUMAN T)

A Ca2+ imaging method has been used to demonstrate simultaneously the magnitude and time course of the increase in the intracellular Ca2+ co ncentration ([Ca2+](i)) in 10-30 individual human peripheral T cells f ollowing stimulation by anti-CD4 or anti-CD8 monoclonal antibody (MAb) as well as anti-CD3 MAb. The rise in [Ca2+](i) began within 10 s of t he introduction of the MAb and reached a peak of 240 nM (mean of 73 ce lls) in 20-40 s. The peak was followed by a slow decrease persisting f or 6-8 min. Comparing Ca2+ responses in the presence and absence of ex ternal Ca2+, the rise in [Ca2+](i) was found to be caused by both tran sient intracellular Ca2+ release and a long-lasting Ca2+ influx from o utside the cell. Cross-linking of CD4 or CD8 using anti-IgG antibody a ugmented the response in individual cells, as seen in the higher peak (365-390 nM) and the longer duration (over 10 min). Simultaneous stimu lation of CD3 and CD4 did not cause a summation of Ca2+ responses but caused a suppression in the CD3-mediated Ca2+ response. The results su pport the view that CD4 and CD8 play a role in signal transduction for T cell activation and that the CD4-derived signal interferes with the CD3-derived signal at some stage in the signalling pathway causing th e Ca2+ response.