INTRACELLULAR SIGNAL-TRANSDUCTION MEDIATED BY LIGATION OF MHC CLASS-IMOLECULES

A great deal of knowledge has accumulated regarding signal transductio n after ligation of MHC class I (MHC-I) molecules. In recent years foc us has been given to delineation of the intracellular signal pathways activated after MHC-I ligation. Activation of tyrosine kinases leading to a rise in the intracellular free calcium concentration ([Ca2+](i)) is the major initial event occurring after MHC-I ligation of T cells. Curiously, the MHC-I-induced signaling is not dependent upon the cyto plasmic tail of the MHC-I molecule, suggesting that the MHC-I molecule induces intracellular signaling through association with other membra ne-embedded molecules. More distal signaling events after MHC-I ligati on includes activation of the Jak/Stat pathway leading to Stat-3 activ ation, and activation of the PIS-kinase leading to JNK activation and apoptosis. This review will sum up what is currently known about signa ling induced by ligation of MHC-I.