Role of crotoxin, a phospholipase A(2) isolated from Crotalus durissus terrificus snake venom, on inflammatory and immune reactions

Background: Crotoxin (CTX) is a potent neurotoxin from Crotalus durissus te rrificus snake venom (CdtV) composed of two subunits: one without catalytic activity (crotapotin), and a basic phospolipase A(2). Recent data have dem onstrated that CdtV or CTX inhibit some immune and inflammatory reactions. Aim: The aim of this paper was to investigate the mechanisms involved in th ese impaired responses. Materials and methods: Male Swiss mice were bled before and at different in tervals of time after subcutaneous injection of CTX or bovine serum albumin (BSA) (control animals). The effect of treatments on circulating leukocyte mobilisation and on serum levels of interleukin (IL)-6, IL-10, interferon (IFN)-gamma and corticosterone were investigated. Spleen cells from treated animals were also stimulated in vitro with concanavalin A to evaluate the profile of IL-4, IL-6, IL-10 or IFN-gamma secretion. Cytokine levels were d etermined by immunoenzymatic assay and corticosterone levels by radioimmuno assay. To investigate the participation of endogenous corticosteroid on the effects evoked by CTX, animals were treated with metyrapone, an inhibitor of glucocorticoid synthesis, previous to CTX treatment. Results: Marked alterations on peripheral leukocyte distribution, character ised by a drop in the number of lymphocytes and monocytes and an increase i n the number of neutrophils, were observed after CTX injection. No such alt eration was observed in BSA-treated animals. Increased levels of IL-6, IL-1 0 and corticosterone were also detected in CTX-injected animals. IFN-gamma levels were not modified after treatments. In contrast, spleen cells obtain ed from CTX-treated animals and stimulated with concanavalin A secreted les s IL-10 and IL-4 in comparison with cells obtained from control animals. Me tyrapone pretreatment was effective only to reverse the neutrophilia observ ed after CTX administration. Conclusions: Our results suggest that CTX may contribute to the deficient i nflammatory and immune responses induced by crude CdtV. CTX induces endogen ous mechanisms that are responsible, at least in part, for these impaired r esponses.