[Study of the mechanisms of rejection in incompatible mollusk-schistosome pairs from infestations by means of a natural route or by microsurgical transplantations of parasitic stages].

The non-compatible host-parasite combination used in these studies is an albino Brazilian strain of Biomphalaria glabrata (BRE) and a Guadeloupean strain of Schistosoma mansoni (GUA). This work allows us to emphasize three main points: --The failure of infestation by miracidia transplantations in the non-compatible combination indicates that the origin of resistance does not lie at the level of the tegument, but further away, in the hemolymph of the host. --The results of the histological studies show that the GUA miracidia are completely destroyed 48 h after a natural infection. In addition to the normal reactions of miracidia encapsulation, a degeneration of miracidia without haemocyte participation has also been demonstrated. This degeneration has been interpreted as an indirect proof of the presence of cytophylic factors against the parasite in the plasma of resistant snails. --The results obtained by means of sporocyst transplantations reveal for the first time in vivo the cytotoxic function of haemocytes from resistant B. glabrata. In addition, in vivo studies have demonstrated that the capacity of granulocytes to lyse cells may be much greater than previously suspected. The marked immune response after non-compatible sporocyst transplantation could allow the use of this infection technique as a test of snail-digenea compatibility.