HLA class II epitope detection by serology.

The amino acid sequence for the Class II specificities on 70 homozygous cell lines was compared with the cytotoxic reactions produced by 13,000 allogenic antisera against these lines. Many of the cytotoxic reaction patterns correlated completely with unique amino acids at a given residue. Therefore, we inferred that the antibodies were reacting directly with these amino acid-defined residues. Among 131 variable DRB1 residues, several well-correlated antisera were found to 64 (49%). Among 94 DQB1 residues, antibodies were found to 59 (63%). The location of these serologically defined epitopes on the molecule is shown in the table. We conclude that much of the serologic reactions of Class II can be explained by reactivity to the amino acid-defined epitopes. It can be shown that many of the sera that were previously considered multispecific are directed against these epitopes. These serologically defined epitopes are clearly immunogenic and are probably important in transplant matching.