Neutralization of dermonecrotic and lethal activities and differences among the principal toxic
proteins (32-35 kDa) of medically important Loxosceles
spider venoms in Brazil (Loxosceles gaucho, Loxosceles laeta and Loxosceles intermedia) were studied using
monoclonal antibodies (MAbs) produced against the dermonecrotic component (35 kDa) of L. gaucho
venom. MAb titers were 512,000 to homologous
venom, between 2000 and 64,000 for L. intermedia
venom and between 1000 and 64,000 for L. laeta
venom. By Western blotting, MAbs could recognize mainly the 35 kDa
protein of L. gaucho
venom and with less intensity the 35 kDa
protein of L. intermedia
venom. These MAbs also recognized weakly or did not recognize the 32 kDa component of L. laeta
venom. Only MoALg1 showed high affinity for L. gaucho
venom and neutralized in vivo 90-97% of the dermonecrotic activity, besides delaying the lethality induced by homologous
venom. MoALg1 maintained its capacity to neutralize the dermonecrotic activity, even when administered (i.v.) 6h after envenoming (i.d.). All MAbs obtained failed to neutralize the toxic activities of the heterologous
venoms.These results suggest that different
epitopes are present in the
protein responsible for the dermonecrotic activity of Loxosceles
venoms, and confirm the participation of other
venom components during the local reaction process. This study also confirms the importance of
antibodies for neutralization of dermonecrotic activity, even when administered some hours after envenoming, and emphasizes the differences of composition and toxicity of medically important Loxosceles
venoms. These findings must be considered in order to improve
loxoscelism immunotherapy.