The definition of a new Ia antigenic specificity using the B6.C-H-2bml2 I-region mutant strain.

A new Ia specificity has been defined using the IA-subregion mutant B6.C-H-2bm12. The immunization to produce the antiserum was bml2 antiA.BY, as all other immunizations, such as bml2 anti-C57BL/6, failed to produce antibody. By selecting strains of C57BL origin for testing, it was shown that, (a) the serum was only weakly cytotoxic but gave substantial reactions using a rosetting assay; (b) the antibody reacted with B cells and not T cells; (c) strains of the b,d,p and q H-2 haplotypes were positive, whereas f,k,r and s were negative; (d) absorption studies demonstrated only a single specificity to be present and by testing recombinant strains, the reaction mapped to the IA subregion; (e) SDS-PAGE demonstrated that the antiserum reacted with a molecule of MW approximately 33,000. Preliminary studies indicate this new specificity, present on C57BL/6 and lost from bml2, is present on the same molecule as other I-A specificities.