Biochemical evidence for multiple I-E Ia molecules.

Sequential immunoprecipitation and isoelectric focusing analyses with monoclonal I-E-specific antibodies presented in this paper indicate the existence of multiple I-E molecules. In sequential immunoprecipitations with 13-4 (anti-Ia.7) and 17-3-3 (anti-Ia.22) monoclonal antibodies, 17-3-3 only partially cleared I-E molecules immunoprecipitated by 13-4. Similarly, 13-4 monoclonal antibody only partially cleared I-E molecules precipitated by 17-3-3 monoclonal antibody. These results suggested a minimum of three I-E molecules. One I-E molecule expresses both 13-4 and 17-3-3 determinants, a second I-E molecule expresses only 17-3-3 determinants, and a third I-E molecule expresses only 13-4 determinants. Isoelectric focusing analyses of I-E molecules immunoprecipitated by 13-4 and 17-3-3 showed differences in both Ae beta polypeptide chains and E alpha polypeptide chains. The sequential immunoprecipitation and isoelectric focusing analyses presented in this paper can be explained by a model in which there are at least two separate Ae genes being encoded within the I-A subregion and two separate E alpha genes being encoded within the I-E subregion. The 17-3-3 monoclonal antibody would recognize a determinant on only one of two Ae beta polypeptide chains and the 13-4 monoclonal antibody would recognize a determinant on only one of two E alpha polypeptide chains.