Tryptic-Peptide Identity of the GPLA-B.1 Alloantigens Derived from Noncongenic Inbred Strain 2 and Strain 13 Guinea Pigs

Abstract

The guinea pig MHC, the GPLA complex, codes for the B and S classic histocompatibility antigens. Four alleles have been postulated at the B locus and two alleles at the S locus. Strain 2 and strain 13 guinea pigs have serologically identical B.1 and S antigens but differ by the I region. However, since these two strains do not have common parentage, it was unknown whether their B.1 molecules were structurally identical. This is an important consideration since the large body of immunogenetic data attributed solely to I region differences is based on this premise and therefore would be subject to reinterpretation if it should prove untrue. We have demonstrated that the primary structures of these two B.1 molecules are identical by performing isoelectric focusing and comparative tryptic-peptide mapping analysis. The DHCB (PCA) guinea pig expresses the same I region as that of the strain 13 guinea pig, but has a different B alloantigen (i.e., B.3). Isoelectric focusing and comparative tryptic-peptide mapping analysis of this B.3 alloantigen have substantiated the serologic finding of nonidentity of the B.1 and B.3 molecules by showing that the two molecules do not share identical primary structure. However, the mapping data showed that there was 40 to 50% homology between the B.1 and B.3 molecules. This result is consistent with the findings in the mouse system for alleles of the same locus. Therefore, our study has demonstrated that the B.1 molecules from the two noncongenic strain 2 and strain 13 guinea pigs are structurally identical and that the B.3 molecule of the DHCBA guinea pig is most likely an allelic product of the B.1 molecule.