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.

HLA epitopes detected by serology.

There is evidence that many of the so-called multispecific cytotoxic antisera react to the amino acid-defined epitopes of the HLA-A and B loci molecules. This evidence is based on the finding that a group of sera produced allelic reactions which corresponded to amino acid substitutions. Antisera for 29 amino acid variants were identified at 67 variable residues on the A locus and for 17 of the 51 variable sites on the B locus. The results were validated by showing that the reactions produced by testing cells from 111 individuals on an epitope typing tray fit the Hardy Weinberg equilibrium. This means that the alleles defined by the antisera behaved as alleles in the random population. Tests of homozygous cells on the epitope typing trays produced completely mutually exclusive reaction patterns as expected on the basis of the amino acid substitutions. Two examples are cited in which immunization across a single HLA "antigen" difference existed between donor and recipient, resulting in a "multispecific" antiserum. The specificities contained in the serum exactly fit an amino acid difference between the donor and recipient.

HLA serologic epitopes.

A total of 25,000 antisera from parous women was evaluated for antibody specificity toward HLA epitopes in the A,B, and C loci. It was determined that most of the reactivity patterns against a large panel could be accounted for by the amino acid substitutions at the known residues. It has been surprising that each of the variable amino acids at each residue against which antisera have been found belonged on either the A, B, or C locus.