C.W. van den Berg

Loxosceles spider venom induces the release of thrombomodulin and endothelial protein C receptor: implications for the pathogenesis of intravascular coagulation as observed in loxoscelism

Summary.  Background: The venom of the spider Loxosceles can cause both local and systemic effects including disseminated intravascular coagulation. Aim: The aim of this study was to investigate the effects of the venom of Loxosceles intermedia (L. intermedia) and the purified Sphingomyelinase D (SMaseD) toxin upon the Protein C (PC) natural anticoagulant pathway. Results: Both the venom and e purified SMaseD reduced the cell surface expression of thrombomodulin (TM) and Endothelial PC Receptor on endothelial cells in culture. The reduction of cell surface expression was caused by cleavage from the cell surface mediated by activation of an endogenous metalloproteinase. Reduction of TM and Endothelial PC Receptor on the surface of these cells resulted in an impaired ability of the cells to assist in the thrombin‐induced activation of PC. Conclusion: This novel observation gives further insight into the mechanisms of the pathology induced by venom from Loxosceles spiders and may aid the development of a suitable therapy.

Characterization of the gene encoding component C3 of the complement system from the spider Loxosceles laeta venom glands: Phylogenetic implications.

A transcriptome analysis of the venom glands of the spider Loxosceles laeta, performed by our group, in a previous study (Fernandes-Pedrosa et al., 2008), revealed a transcript with a sequence similar to the human complement component C3. Here we present the analysis of this transcript. cDNA fragments encoding the C3 homologue (Lox-C3) were amplified from total RNA isolated from the venom glands of L. laeta by RACE-PCR. Lox-C3 is a 5178 bps cDNA sequence encoding a 190kDa protein, with a domain configuration similar to human C3. Multiple alignments of C3-like proteins revealed two processing sites, suggesting that Lox-C3 is composed of three chains. Furthermore, the amino acids consensus sequences for the thioester was found, in addition to putative sequences responsible for FB binding. The phylogenetic analysis showed that Lox-C3 belongs to the same group as two C3 isoforms from the spider Hasarius adansoni (Family Salcitidae), showing 53% homology with these. This is the first characterization of a Loxosceles cDNA sequence encoding a human C3 homologue, and this finding, together with our previous finding of the expression of a FB-like molecule, suggests that this spider species also has a complement system. This work will help to improve our understanding of the innate immune system in these spiders and the ancestral structure of C3.