T cell signal transduction and the role of CD7 in costimulation

The complex cellular interactions that govern the mammalian immune response are now known to include specific receptor/ligand interactions, recruitmen t of intracellular signaling molecules, activation of both kinases and phos phatases, and redistribution of macromolecular complexes into specific subc ellular membrane locations that, in aggregate, result in transcriptional ac tivation. While the TCR-CD3 signal is critical for activation of the restin g T cell, it alone is not sufficient to initiate transcriptional activation or generate an effective immune response. A number of other coreceptor mol ecules, including CD4, CD8, and CD28, have now been characterized that also play important roles in initiating or amplifying the activation of the T c ell. A 40 kDa member of the immunoglobulin superfamily, the CD7 molecule, h as also been shown to have costimulatory activity and to induce tyrosine an d lipid kinase activities. Here we will review the signaling pathways initi ated by TCR, CD28, and CD7, as well as the functional consequences of signa l transduction through these receptors.