ANALYSIS OF THE MECHANISMS INVOLVED IN THE DEVELOPMENT OF CUTANEUS LOXOSCELISM IN VIVO

PAIXÃO-CAVALCANTE, D.(1), GONÇALVES DE ANDRADE, R.M.(1), ANTONIAZZI, M.M.(2), MAGNOLI, F.C.(1), VAN DEN BERG, C.W.(1,3), TAMBOURGI, D.V.(1)

Laboratories of Immunochemistry(1) and Cell Biology(2), Butantan Institute, São Paulo, Brazil and (3)Department of Pharmacology, Therapeutics and Toxicology, University of Wales, College of Medicine, Cardiff, UK

Envenomation by spiders belonging to the genus Loxosceles commonly results in impressive local necrotic skin lesions and, more rarely, causes systemic effects, including profound intravascular haemolysis. The predominant clinical sign is a cutaneous reaction characterised by the appearance of necrosis around the bite, resulting in ulceration. In this work, we undertook a histopathological characterization of the dermonecrotic lesion produced experimentally with Loxosceles intermedia venom and evaluated the role of the complement system and endogenous proteases in the development of cutaneous loxoscelism.  Adult rabbits were injected intradermally with 5 g of L. intermedia venom or P1 toxin in the presence of 10 mM EDTA, 1,10phenanthroline or PMSF. Alternatively, rabbits were depleted of complement by i.v. injection of cobra venom factor and then inoculated with venom. Twenty-four hours after venom inoculation, the rabbits were sacrificed and the skin was removed for histopathological analysis. Rabbits inoculated with L. intermedia venom showed an intense inflammatory cell migration into the dermis. In the sub-epidermal region, haemorrhage and disorganization of the collagen fibres was observed. The skin muscle layer showed an intense inflammatory cell influx and haemorrhage. Rabbits inoculated with P1 toxin showed the same histopathological profile as those injected with the venom. Complement depleted rabbits showed a large reduction in the inflammatory cell infiltration into the inoculated site. Both 1,10phenanthroline and EDTA inhibited the haemorrhage and influx of inflammatory cells whereas PMSF was unable to revert any of the effects provoked by the venom. P1 toxin had the same ability as venom to induce dermonecrotic lesions. These results reinforce the idea that the sphingomyelinase toxin P1 is the initiator of the dermonecrotic reaction. The complement system and endogenous metalloproteinases are also involved in the development of the lesion induced by L. intermedia venom. 

Supported by FAPESP and The WellcomeTrust. 

CORRESPONDENCE TO:

Danielle Paixão Cavalcante, Avenida Carceal Motta ,1310, São Paulo, SP, CEP: 05101-210, Brasil, Email: danipaixao@yahoo.com.br