Short communication Sex-linked variation of Loxosceles intermedia spider venoms KaÂtia Cristina de Oliveira, Rute M. Gonc ° alves de Andrade, Adriana L. Giusti, Wilmar Dias da Silva, Denise V. Tambourgi * Laboratory of Immunochemistry, Butantan Institute, Av. Vital Brasil, 1500, CEP 05508-900 Butanta Ä, Sao Ä Paulo, SP, Brazil Received 6 January 1998; accepted 20 April 1998 Abstract In order to investigate intraspeci®c dierences in Loxosceles intermedia spider venom we compared some biological properties of male and female venoms. Females produced higher amounts of venom than males. Furthermore, female venom presented more potent dermonecrotic and complement-dependent activities than male venom. Interestingly, the F35 toxin, a dermonecrotic and complement-dependent haemolytic factor, was also present in greater amounts in female venom, as demonstrated by ELISA. Therefore, the higher production and increased toxicity of venom in female specimens as compared to males may contribute to the variability observed in the severity of envenoming caused by L. intermedia spiders. # 1998 Elsevier Science Ltd. All rights reserved. Envenomation by spiders of the genus Loxosceles may result in necrotic lesions and systemic reactions, including haemolytic anaemia, haemoglobinemia, jaundice, haemoglobinuria, renal failure and death. In previous works we demonstrated that the main toxic component of L. intermedia venom is a protein of 35 kDa, named F35. This component which was characterised as an inducer of complement mediated haemolysis and as a dermonecrotic factor, was lethal to mice (Tambourgi et al., 1995). We also veri®ed that the signals and lesions produced in mice by L. intermedia venom, or by the F35 toxin, mimic the state of endotoxemic shock in humans and that the extent of Toxicon 37 (1999) 217±221 0041-0101/98/$ - see front matter # 1998 Elsevier Science Ltd. All rights reserved. PII: S0041-0101(98)00130-5 PERGAMON * Author to whom correspondence should be addressed.