Subset analysis of human class II molecules controlled by the DR2/Dw2 haplotype: two separate DR subsets carry the DR2 specificity.

Human class II molecules were isolated from cells of a DR2/Dw2-homozygous cell line, PGF. The three mutually exclusive subsets were separated by selective binding with monoclonal antibody MCS7 and alloantisera CCB921 and KY22. The specificity involved in the binding with alloantisera was identified to be a supertypic specificity associated with DR1, 2, and w9 for CCB921 and the DQw1 specificity known to be associated with DR1, 2, w6, and w10 for KY22. The MCS7 specificity appeared to be a cross-reactive specificity related to the DRw52-like specificity. On peptide mapping, the alpha chains of MCS7- and CCB921-reactive subsets were the same, showing the pattern characteristic of DR alpha chains, whereas the beta chains were very similar to, but distinguishable from, each other. These structural features conformed to those of DR or DR-like subsets. The KY22-reactive subset was distinctive in both alpha and beta chains from the above two subsets, and it displayed peptide patterns typical to DQw1-bearing Ia molecules. Interestingly, the MCS7- and CCB921-reactive subsets both carried the DR2 specificity, as indicated by their binding to alloantiserum Fe73/22 which was proven to be DR2-specific.