Signal transduction in T cells.

Rapid progress was made during the past year in the delineation of the nature of the initial biochemical events triggered by the T-cell antigen receptor. Antigen-mediated activation of phospholipase C was demonstrated to require protein tyrosine phosphorylation and, most surprising, activation of the Ras family of signal transduction molecules was shown to closely follow stimulation of the T-cell antigen receptor. Major controversy continues over which events are relevant to the various effector functions of T cells.