Evidence for β ₂-microglobulin-like and H-2-like antigenic determinants in Drosophila

Serologic evidence for the existence of β ₂-microglobulin-, (β ₂m) like and H-2-like antigenic determinants in Drosophila are presented. Drosophila-cultured cells and larvae extract were shown to react specifically with a rabbit anti-rat β ₂m and a rabbit anti-mouse β ₂m antisera. G-200 pooled fractions from Drosophila larvae were shown to react with β ₂m-eluted and glycin-absorbed antisera, but not with β ₂m-absorbed or glycin-eluted antisera. These fractions also quantitatively inhibited the heterologous reaction between the anti-β ₂m antisera and purified human and rat β ₂m. The lack of reactivity of other rabbit antisera or normal serum with Drosophila, as well as the efficiency of absorption of anti-β ₂m reactivity by either rat of KCO% (Drosophila) cells, further supports the presence of β ₂m epitopes on Drosophila cells. Data are also presented showing that certain anti-H-2 alloantisera react with Drosophila. That this reactivity is indeed due to anti-H-2 antibodies is suggested by several lines of evidence, including the removal of cytotoxic alloantibodies and lack of reactivity by other mouse antisera and monoclonal reagents. Preliminary data suggest that the H-2-like and β ₂m-like determinants are physically associated on the cell surface of Drosophila cells. These findings have important implications on current concepts concerning the evolutionary origin and physiologic role of β ₂m and the major histocompatibility complex.