Structural compartmentalization of MHC class II signaling function.

Major histocompatibility complex (MHC) class II molecules are critical restricting elements in the generation of thymus-dependent immune responses. Recent studies indicate that in addition to providing a composite epitope for recognition by T-cell antigen receptors, MHC class II molecules function in signal transduction through interaction with other cellular proteins. Mutational analyses indicate that structural information necessary for these functions is compartmentalized in different aspects of the molecular complex. Here, William Wade and colleagues review the structural basis of this MHC class II function as defined in the I-A alpha and -beta chains.