Activation of vertebrate complement by Helix pomatia haemolymph

Haemolymph plasma from the pulmonate snail Helix pomatia contains a constituent, not yet identified, which causes activation of vertebrate complement via the alternative complement pathway in fluid phase. The activation of vertebrate complement by snail plasma is closely analogous to the activation caused by cobra venom factor (CVF), the snake's C3b, with one notable exception; the snail factor requires vertebrate C3 for the formation of C3 convertase which cobra venom factor does not. Our results do not allow any definite conclusion on the exact mechanism but we favour the idea that the haemolymph contains a complement-like protein which functions as an opsonin in the snail, and which can interact with vertebrate alternative complement pathway components.