Cross-reactions of Ia antigens between mouse and man.

Murine alloantisera with specificity for the I-region of the MHC were found to cross-react with human B lymphocytes. By using antisera selected for subregion specificity and including monoclonal antibodies, antisera directed to I-E/Ck products were shown to have the greatest cross-reactivity with human cells. In the reciprocal direction, human anti-DRw alloantisera were also found to contain antibodies that reacted with murine B lymphocytes, and by using congenic strains this reaction was shown to be MHC restricted and was of the "Ia type." By studying appropriate intra-H-2 recombinant strains. The reactivity could be mapped to the 1-E subregion (especially to 1-Ek). In addition, antibodies to the murine 1-Ek subregion could specifically block the reaction of the two DRw antisera examined; whereas, anti-I-Ak antisera were without effect. These studies further highlight the unique cross-reactions between two highly polymorphic gene produces in mouse and man, and demonstrate that the 1-E subregion in the mouse codes for the most cross-reactive specificities.