Preliminary observations on a hemolymph factor influencing the infectivity of Schistosoma mansoni miracidia

It has been demonstrated that the infectivity of Schistosoma mansoni miracidia for a highly susceptible strain of Biomphalaria glabrata was reduced markedly when the miracidia were pretreated with hemolymph from the snail Helisoma caribaeum. Although the Helisoma hemolymph factor(s) responsible for this phenomenon has not been identified with certainty, it appears to be a snail lectin associated with binding sites for n-acetyl-D-glucosamine on the surface of the miracidium. Hemolymph from uninfected and infected B. glabrata and from a resistant strain of B. glabrata did not reduce the infectivity of miracidia, nor did pretreatment with bovine plasma albumin. Likewise, we demonstrated that reduction of miracidial infectivity was not due to the presence of a miracidial immobilizing factor found in the hemolymph of many snail species. Differences in the infectivity between pretreated miracidia and controls were statistically significant (P = 0.001).