INCORPORATION OF A 35-KILODALTON PURIFIED PROTEIN FROM LOXOSCELES INTERMEDIA SPIDER VENOM TRANSFORMS HUMAN ERYTHROCYTES INTO ACTIVATORS OF AUTOLOGOUS COMPLEMENT ALTERNATIVE PATHWAY

Cutaneous inoculation of Loxosceles spp. spider venoms produces local necrosis, occasionally accompanied by systemic intravascular clotting and hemolysis. In this work, we analyzed the role of the C system on t he lysis of human erythrocytes (E(h)) induced by Loxosceles venoms in vitro. E(h) were treated with whole venom of Loxosceles laeta, Loxosce les gaucho, or Loxosceles intermedia, or with purified venom proteins, and incubated with C-sufficient (Cs-NHS) or C9-depleted autologous (C 9d-NHS) serum. Hemolysis was determined spectrophotometrically, and de position of C components or removal of C regulatory proteins was analy zed by FACS. E(h) suspensions exposed to venoms or to a purified 35-kD a protein from L. intermedia were lysed after incubation with Cs-NHS, but not with C9d-NHS. Lysis was blocked by heating the serum at 50 deg rees C or Ca2+/Mg2+ chelation by EDTA, but not by Ca2+ chelation with EGTA. Deposition of C1, C2, C3, C4, C5, and factor B on the venom-trea ted E(h) occurred during activation of autologous C. Regulatory protei ns decay-accelerating factor (DAF) and CD59 were not altered significa ntly. Conversion of C-resistant E(h) into C-susceptible E(h) by the L. intermedia venom was accompanied by incorporation of a 35-kDa venom p rotein onto the cell surface. Thirty-five-kilodalton-related proteins were detected in the two other Loxosceles venoms by ELISA, using rabbi t antiserum against the L. intermedia 35-kDa protein. These data sugge st that the C system mediates the lysis of human erythrocytes and, by extension, of other cell types able to incorporate the lytic factor of Loxosceles venoms on their cell surfaces.