αβT cell receptor and CD3 transduce different signals in immature T cells. Implications for selection and tolerance

Ligand binding to αβTCR has different consequences in thymocytes at different developmental stages, causing alternatively positive selection, clonal deletion, or activation. These various functional consequences may be due to changes in the signaling properties of the receptor complex during development. In this report we show that αβTCR engagement on immature thymocytes has different effects on intracellular free calcium concentrations than αβTCR engagement on mature T cells. In contrast, CD3 engagement on immature thymocytes and mature T cells has the same effect on intracellular free calcium, suggesting that altered signal transduction in immature thymocytes may be due to inefficient αβTCR-CD3 coupling. These studies also suggest that in certain T cell populations, activation events resulting from ligation of CD3 may not accurately reflect the activation events resulting from ligation of the physiologic receptor, αβTCR.