Role of human decay-accelerating factor in the evasion of Schistosoma mansoni from the complement-mediated killing in vitro.
Decay-accelerating factor (DAF) is a 70-kD membrane glycoprotein that prevents complement (C)-mediated hemolysis by blocking the assembly or accelerating the decay of C3 convertase. Purified DAF is known to incorporate into the membrane of DAF-deficient cells, inhibiting lysis. Since Schistosoma mansoni is a blood-dwelling parasite, we investigated whether DAF can be transferred from human erythrocytes to the worm and protect it against C-mediated killing in vitro. We have found that schistosomula (schla) incubated with normal human erythrocytes (N-HuE), but not with DAF-deficient erythrocytes, become resistant to C damage in vitro. Protected parasites acquire a 70-kD surface protein which can be immunoprecipitated by anti-DAF antibodies. The acquired resistance is abrogated by treatment of N-HuE-incubated parasites with anti-DAF antibody. These results indicate that, in vitro, N-HuE DAF can be transferred to schla, and suggest its participation in preventing their C-mediated killing. This could represent an important strategy of parasites to evade the host's immune response in vivo.
Horta
M F
MF
Department of Biochemistry-Immunology, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
Ramalho-Pinto
F J
FJ
Fatima
M
M
D000818:Animals; D001798:Blood Proteins / Q000032:analysis / Q000172:deficiency / Q000502:physiology*; D018958:CD55 Antigens; D002478:Cells, Cultured; D003169:Complement Inactivator Proteins / Q000502:physiology*; D003165:Complement System Proteins / Q000276:immunology*; D004912:Erythrocytes / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D008565:Membrane Proteins / Q000032:analysis / Q000172:deficiency / Q000502:physiology*; D011402:Pronase / Q000494:pharmacology; D011817:Rabbits; D012550:Schistosoma mansoni / Q000276:immunology*; D014357:Trypsin / Q000494:pharmacology
D001798:Blood Proteins; D018958:CD55 Antigens; D003169:Complement Inactivator Proteins; D007074:Immunoglobulin G; D008565:Membrane Proteins; D003165:Complement System Proteins; D014357:Trypsin; D011402:Pronase