Sharing Ia antigens between species. III. Ia specificities shared between mice and human beings.

Certain mouse alloantisera have been found to detect immunologic cross-reactions between human and murine Ia antigens. Almost every anti-Iaa, -Iak and -Iad serum tested exhibited such cross-reactions. Sera prepared against the products of limited segments of the mouse I region and tested on human B cells revealed that anti-I-E/Ck cross-reactions were more readily detectable than anti-I-A, B, Jk cross-reactions. Most of the mouse alloantisera were cytotoxic to bells from almost every individual tested, although a few sera exhibited more restricted patterns of lysis, permitting limited segregation analyses. The cytotoxicity of these mouse alloantisera in family studies was consistent with HLA linkage of the genes responsible for the cross-reacting Ia determinants. Immunochemical analysis on radiolabelled detergent lysates of human lymphocytes indicated that the sera reacted with molecules of 34,000 and 28,000 daltons. Thus, by cellular distribution, HLA association, and immunochemical criteria, these mouse alloantisera detect human Ia antigens. These cross-reactive sera should be of practical value for the detection of human Ia antigens and may also have theoretical implications for the evolution of genes coding for Ia antigens.