THE NECROTIC VENOM OF THE BROWN RECLUSE SPIDER INDUCES DYSREGULATED ENDOTHELIAL CELL-DEPENDENT NEUTROPHIL ACTIVATION - DIFFERENTIAL INDUCTION OF GM-CSF, IL-8, AND E-SELECTIN EXPRESSION

Brown recluse spider (Loxosceles reclusa) venom induces severe dermone crotic lesions. The mechanism for this is unknown but presents an inte resting paradox: necrosis is completely dependent on the victim's neut rophils, yet neutrophils are not activated by the venom. We show Laxos celes venom is a potent, but disjointed, endothelial cell agonist. It weakly induced E-selectin expression, but not intercellular adhesion m olecule-1 or IL-6 expression, yet significantly stimulated release ofI Ln-8 and large amounts of GM-CSF by 4 h. In contrast, TNF strongly ind uced all of these, except for GM-CSF. PMN bound to E-selectin on venom -activated endothelial cells, apparently via counterreceptors differen t from those that bind E-selectin on TNF alpha-activated monolayers. N otably, PMN bound venom-activated monolayers only at intercellular jun ctions, did not polarize, and completely failed to migrate beneath the monolayer. Despite this, bound PMN demonstrated increased intracellul ar Ca2+ levels and secreted primary and secondary granule markers. The latter event was suppressed by sulfones used to treat envenomation. W e have defined a new endothelial cell agonist, Loxosceles venom, that differentially stimulates the inflammatory response of endothelial cel ls. This, in turn, leads to a dysregulated PMN response where adhesion and degranulation are completely dissociated from shape change and tr ansmigration.