Receptor for Fc on the surfaces of schistosomes

Schistosoma mansoni masks its surface with adsorbed host proteins including erythrocyte antigens, immunoglobulins, major histocompatibility complex cl ass I, and beta (2)-microglobulin (beta (2)m), presumably as a means of avo iding host immune responses, How this is accomplished has not been explaine d. To identify surface receptors for host proteins, we biotinylated the teg ument of live S, mansoni adults and mechanically transformed schistosomula and then removed the parasite surface with detergent, Incubation of biotiny lated schistosome surface extracts witt l human immunoglobulin G (IgG) Fc-S epharose resulted in purification of a 97-kDa protein that was subsequently identified as paramyosin (Pmy), using antiserum specific for recombinant P my, Fc also bound recombinant S. mansoni Pmy and native S. japonicum Pmy, A ntiserum to Pmy decreased the binding of Pmy to Fc-Sepharose, and no protei ns bound after removal of Pmy from extracts. Fluoresceinated human Fe bound to the surface, vestigial penetration glands, and nascent oral cavity of m echanically transformed schistosomula, and rabbit anti-Pmy Fab fragments ab lated the binding of Fc to the schistosome surface, Pmy coprecipitated with host IgG from parasite surface extracts, indicating that complexes formed on the parasite surface as well as in vitro. Binding of Pmy to Fe was not i nhibited by soluble protein A, suggesting that Pmy does not bind to the reg ion between the CH2 and CH3 domains used by many other Fc-binding proteins. beta (2)m did not bind to the schistosome Fc receptor (Pmy), a finding tha t contradicts reports from earlier workers but did bind to a heteromultimer of labeled schistosomula surface proteins, This is the first report of the molecular identity of a schistosome Fc receptor; moreover it demonstrates an additional aspect of the unusual and multifunctional properties of Pmy f rom schistosomes and other parasitic flatworms.