Recombinant human IFN alpha 2b coupled to a silica support was used for the purification of the IFN alpha -binding proteins from placental cell membrane extracts. The 100-kDa (p100) and 64-kDa (p64) proteins, which bind preferentially to an IFN alpha ab-silica matrix, were identified. Using a monoclonal antibody (A6) against IFN-gamma R1, it was able to isolate p100 and p70, but only if IFN alpha 2b was present during chromatography. Similar interactions were observed using polyclonal antibody anti-IFN gamma binding proteins, as assayed in Western blot, These interactions were identified as conformation dependent, We speculate that IFN alpha 2b receptor complex shares an IFN gamma receptor complex epitope. (C) zool. Academic Press.