Assignment of antigenic determinants to separated I-A kappa chains.

The alpha- and beta-chains of the I-A kappa antigen from the AKTB-1b B cell lymphoma were separated by ion-exchange chromatography on CM-Sephadex in the presence of propionic acid and urea. Removal of the denaturants by dialysis produced isolated chains that regained a significant amount of their native configuration. These materials were used with a battery of monoclonal antibodies in a direct binding assay to localize specific alloantigenic determinants to the A alpha kappa or A beta kappa chains. This method allowed the assignment of the nominal specificity Ia. 17 and at least one epitope of the specificity Ia.2 to the A beta kappa chain. Finally, the I-A kappa antigen from the B cell lymphoma AKTB-1b was shown to be identical, by the criterion of tryptic peptide analysis, to that derived from normal B10.BR splenocytes. This constitutes the first demonstration that the polypeptide portion of a tumor-derived class II MHC antigen is identical to that derived from a normal tissue.