Biochemical characterization of murine Ia antigens with xenoantisera - I. Identification of a second Ia molecule (I-E?) in H-2^s haplotype

Rabbit anti-Ia sera was produced by immunization with detergentsolubilized extracts from splenic, lymph-node and thymus cells. The antisera contained activity against H-2 as well as Ia molecules. By a sequential immunoprecipitation assay it was shown that the rabbit anti-mouse H-2^s serum precipitated a second Ia molecule in the H-2^s haplotype. Previous studies with alloantisera have shown only one Ia molecule associated with this haplotype. Sequential precipitations with alloantiserum against the whole I region were used to show that this second Ia molecule is coded by genes within the I region. Since only I-A- and I-E-region coded molecules are immunoprecipitable in most haplotypes, we presume that the rabbit antiserum could be identifying the I-E-subregion coded molecule in the H-2^s haplotype. The rabbit antiserum reacts with an isotypic specificity on the molecule. The studies suggest that the I-E subregion does exist in the H-2^s haplotype even though alloantiserum cannot be produced to identify allotypic variants associated with this subregion.