CHEMICAL CROSS-LINKING OF IA ALLOANTIGEN ALPHA-CHAINS AND BETA-CHAINS WITH DIMETHYL 3,3'-DITHIOBISPROPIONIMIDATE

Abstract

The polypeptide chain composition of membrane-bound and detergent-solubilized Ia [immune response-associated] antigens was examined using the chemical cross-linking reagent dimethyl 3,3''-dithiobispropionimidate (DTBP). Products of the I-E/C subregion of the [mouse] major histocompatibility complex, which were solubilized from spleen cells with the detergent NP-40 and partially purified by affinity chromatography on lentil lectin-agarose, could be almost completely cross-linked by DTBP. The characteristic 33,000 MW (.alpha.) and 28,000 (.beta.) polypeptide chains seen on sodium dodecylsulfate polyacrylamide gels disappeared and a major new species of 60,000 MW appeared after cross-linking. When isolated and reduced with 2-mercaptoethanol, the 60,000 MW peak was comprised of .alpha. and .beta. chains. Similar results were obtained when I-E/C and I-A .alpha. and .beta. chains were cross-linked on the cell surface. The .alpha. and .beta. chains of the Ia antigens exist primarily in the form of a dimer in detergent solution and in situ.