The multideterminant nature of the HLA-B gene product : a serological study
The nature and extent of the serological cross-reactivity of HLA-B antigens was investigated using lymphocytotoxic antisera produced by pregnancy alone. Particular attention was focused on the HLAB14 antigen and its cross-reactive group. Investigations were made using reference lymphocyte panel and population analyses, family studies and sequential absorption, elution and lysostrip techniques. Parameters of the F(ab')2 fragment blocking technique were investigated and a standard method was developed for the study of HLA-B determinant topography. The immunizing antigen responsible for stimulating each antiserum was identified. A method was devised for the analysis of antiserum component specificity association. This showed the significant non-random occurrence of groups of specificities within the reaction ranges of broad antisera produced by one HLA-B antigen. An examination of the HLA antigens of the serum donors showed that many possess antigens `cross-reactive' with their immunizing antigen, and also that they appeared to modify the reaction range of the responders' antisera. Genes within the MHC appear to influence the humoral response to HLA-B molecules as was shown by a comparison of the HLA-A B and Bf antigen frequencies in the responders with the frequencies found during a population genetics analysis of a random population. Two serologically distinct forms of the HLA-B14 antigen (Bw64 and Bw65) were established. These showed different linkage disequilibria between HLA-A, DR and Bf alleles. In addition, distinct HLA-A, DR, Bf, C4A and C4B haplotypes bearing Bw64 or Bw65 were identified. Blocking studies indicated that a common determinant, which is separate from a Bw64 or Bw65 site, is shared by both B14 subtype molecules. Additional determinants that B14 shares with B8, B18 and B39/38 are distinct from the Bw64/Bw65 site, being variably associated with the B14 common determinant but closely adjoining the Bw6 antigen. Studies involving a unique B45 antiserum showed that B44 and B45 are distinct specificities that share a common structure. Five major `cross-reactive groups' of HLA-B antigens were distinguished, viz, B7, B12, B14, B17 and B40; their serological inter-relationships and the `cross-reactive' symmetry of the antisera they produce was characterized. The findings emphasize the complexity of HLA alloantisera and the multideterminant nature of HLA antigens and indicate that in addition to their unique determinants different HLA-B molecules possess several identical determinants together with sites that are structurally similar. This investigation allows the serological view of HLA-A, B antigens derived from alloantisera, to be reconciled with the new image of these antigens obtained from current monoclonal antibody and biochemical studies.