Ia antigenic specificities are oligosaccharide in nature: hapten-inhibition studies.

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Abstract
It was previously reported that the [mouse] Ia [immune response-associated) specificities, coded for by the I region within the H-2 complex, appear to consist predominantly of carbohydrate. This conclusion was reached by examining low MW Ia-bearing oligosaccharides isolated from mouse serum. Using hapten-inhibition studies in this report, it was shown that the binding of allogeneic and xenogeneic anti-Ia antibodies to the Ia glycoproteins found predominantly on B [bone marrow-derived] lymphocytes can be specifically inhibited by certain free sugars. Both inhibition assays revealed that the specificity for the following Ia antigens resides predominantly in the following sugars: Ia.1: N-acetyl-D-mannosamine or related sugars, Ia.3: .alpha.-D-galactose and related sugars, Ia.7: L-fucose and Ia.15: N-acetyl-D-glucosamine. These sugars are apparently found at the terminal nonreducing ends of the carbohydrate portion of the Ia-bearing glycoproteins present in the lymphocyte membrane. Several public and private H-2 antigenic specificities did not appear to be sugar defined. These studies imply that at least some of the Ia genes from the I-A and I-C subregions of the I region code for glycosyl transferases which modify oligosaccharide structure and impart specificity to the Ia antigens by alteration of their terminal sugar residues.