title: Antibody-independent activation of the alternative complement pathway in human serum by parasitic cells.
abstract: The lysis of the monocellular parasite Trypanosoma cyclops by normal human serum (NHS) was found to be complement-dependent and to follow activation of the alternative pathway without apparent requirement for conventional antibodies. Lysis of the organisms was inhibited by heat-inactivating NHS at 56 degrees, preincubation of NHS with cobra venom factor or chelation of divalent cations with EDTA. It took place, however, in human C2-deficient serum and was inhibited by prior heating of NHS at 52 degrees to destroy the activity of factor B of the alternative pathway. Moreover, the lytic reaction was magnesium- but not calcium-dependent. Repeated low-temperature (0 degrees) absorption of either human hypogammaglobulinaemic serum or NHS with the parasite failed to remove or significantly decrease their lytic activities.
mesh_terms: D003165:Complement System Proteins / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D007111:Immunity, Cellular; D008274:Magnesium; D014345:Trypanosoma
chemical_list: D003165:Complement System Proteins; D008274:Magnesium