In vitro phagocytosis of foreign particles by amoebocytes from the haemolymph of Helix aspersa (Müller) was studied.
Results showed the presence of an opsonin in Helix serum. This opsonic effect of serum is due to the adsorption of serum component(s) on to the foreign particles. No phagocytosis occurs in the absence of these factors.
There was some degree of specificity of the opsonin for two different foreign particles: formalized yeast cells (Saccharomyces cerevisiae) and formalized sheep red blood cells