The importance of cross-reactions between species: mouse allo-anti-Ia monoclonal antibodies as a powerful tool to define human Ia subsets.

Three mouse allo-anti-Ia monoclonal antibodies recognizing epitopes specific for either I-E gene products (H81.98.21 and H40.315.7 Mabs) or shared between I-E and I-A gene products (H82.246.3 Mab) were used to analyze the human Ia molecules against which they cross-react. The results indicated that in the Ia pool of the human B cell line Raji the three Mabs were able to recognize at least three distinct subsets differing each other both in their alpha as well as in their beta subunits. The comparison with the previously defined human Ia subsets NG1, NGe, and DC1 suggested the following similarities: H81.98.21 specific Ia molecules similar to NG1; H82.246.3 specific Ia molecules similar to NG2, and including probably NG1; H40.315.7 specific molecules similar to DC1 in their alpha subunits and probably heterogeneous in their beta subunits with characteristics of the DC1, NG1, and NG2 subunits altogether. The heterogeneity of the human Ia molecules and the possible similarities with the mouse Ia system were discussed.