Hybrid (combinatorial) Ia specificities: gene complementations to generate Ia.22.

Ia specificity 22 is expressed on a hybrid I-E molecule formed by the association of a beta chain (Ae) coded for by the I-A subregion and an alpha chain (E alpha) encoded by the I-E subregion. Ia.22 can be generated by the complementation of Ab, Ak, As, Ar, with Ed, Ek, Ep, Er, Ew3, Eu, Ev but Eb, Ef, Eq, and Es. With the exception of H-2p which does not complement with As to generate Ia.22, all Ia. 7-positive (I-E) haplotypes can provide the permissive E alpha allele. It is postulated that Ia.22 is a combinatorial Ia determinant generated by the association of the alpha and beta chains. These determinants are probably involved in the immune recognition of antigens under dual Ir-gene control.