An H-2 haplotype possibly derived by crossing-over between the (A α A β ) duplex and the E βlocus

Abstract

The B10.STA62 strain carries the H-2^w27 haplotype derived from a wild mouse captured in the vicinity of Ann Arbor, Michigan. Products of two class II loci composing this haplotype, A_α and A_β, are serologically, biochemically (by tryptic peptide mapping), and functionally indistinguishable from products controlled by the A _α ^b and A _β ^/b genes of the B10.A(5R) strain. In contrast, the polypeptide chain controlled by the third class II locus, E_β, is different from that controlled by the E _β ^/b gene. This E _β ^/w27 chain lacks an antigenic determinant present on the E^b molecule and carries determinants lacking on the E^b molecule, the E _β ^/b and E _β ^/w27 peptide maps differ in at least six peptides, and cytotoxic T cells specific for the E _β ^b chains do not react with B10.STA62 target cells. This great difference between the E _β ^/b and E _β ^/w27 chains suggests that the corresponding genes have not been derived from one another by a direct mutational conversion; instead, H-2^w27 appears to be a recombinant haplotype derived by crossing-over between the A_αA_βduplex and the E_βlocus. This is the first recombinant discovered separating these class II loci.