Murphy, David

Abstract The chain specificities of 18 Ak and 26 Ab-reactive anti-Ia monoclonal antibodies have been determined. L cells were transfected with haplotype-matched (A alpha k:A beta k, A alpha b:A beta b) or haplotype-mismatched (A alpha k:A beta b, A alpha b:A beta k) cDNA pairs, lines expressing high levels of surface A complex were selected, and antibody reactivity with a panel of reagents was assessed by cytofluorimetric analysis. Most of the antibodies recognized a determinant specified by one chain, either alpha or (more commonly) beta. A few examples of more complex determinants were also observed. A knowledge of the chain specificities of anti-Ia monoclonal antibodies should prove useful for a variety of studies aimed at dissecting Ia structure-function relationships.

To identify which polymorphic residues determine the allospecific antibody binding sites on A beta polypeptides, mutant Ak beta genes were constructed encoding single or multiple amino acids of the d allele at 14 polymorphic positions in the beta 1 domain. Cell lines expressing these genes were analyzed by quantitative immunofluorescence using 16 mAbs reactive to Ak beta or Ad beta. Substitution of d allele residues at positions 63 and 65-67 in the Ak beta polypeptide resulted in the loss of binding of all Ak beta-reactive antibodies and the gain of binding of most Ad beta-reactive antibodies. Two Ad beta-reactive mAbs bound to the mutant Ak beta polypeptide containing d allele-characteristic residue at position 40. In contrast, substitution of the other polymorphic residues in the NH2-terminal and COOH-terminal regions of the beta 1 domain did not alter antibody binding.