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 the lysis of human erythrocytes (Eh) induced by Loxosceles
venoms in vitro. Eh were treated with whole
venom of Loxosceles laeta, Loxosceles gaucho, or Loxosceles intermedia, or with purified
venom proteins, and incubated with C-sufficient (
Cs-NHS) or C9-depleted autologous (C9d-NHS) serum.
Hemolysis was determined spectrophotometrically, and deposition of C components or removal of C regulatory
proteins was analyzed by FACS. Eh
suspensions exposed to
venoms or to a purified 35-kDa
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 degrees 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-treated Eh occurred during activation of autologous C. Regulatory
proteins decay-accelerating factor (DAF) and CD59 were not altered significantly. Conversion of C-resistant Eh into C-susceptible Eh by the L. intermedia
venom was accompanied by incorporation of a 35-kDa
venom protein onto the cell surface. Thirty-five-kilodalton-related
proteins were detected in the two other Loxosceles
venoms by ELISA, using rabbit antiserum against the L. intermedia 35-kDa
protein. These data suggest 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.