Factors affecting adoptive transfer of resistance to Schistosoma mansoni in the snail intermediate host Biomphalaria glabrata

We examined potential variables affecting adoptive transfer of resistance t o Schistosoma mansoni in Biomphalaria glabrata implanted with amebocyte-pro ducing organs (APOs) from resistant snails. Transplants of 7 tissues other than the APO (heart, kidney, mantle, albumin gland, brain, digestive gland, and gonad) did not transfer resistance, suggesting a unique property of th is structure. Only APOs from donors previously exposed to miracidia transfe rred resistance, although whether this is evidence for a priming effect or merely the elimination of susceptible donors is not known. Variability in t he donor and in the implant itself apparently was unimportant, inasmuch as implants from small or large snails or from 2 separate donors all conferred similar levels of resistance. Recipients of APOs from 2 additional resista nt strains of B. glabrata, 10-R2 and Salvador, also displayed resistance. H owever, no resistance was transferred by APOs from schistosome-refractory B . obstructa. Histological examination of implants removed from recipients t hat either did or did not show transferred resistance revealed no differenc es in mitotic activity. Furthermore, implanted APOs from B, obstructa displ ayed no mitotic activity. Finally, reexposure of snails with transferred re sistance to a large dose of miracidia caused infection in 70%, suggesting t hat either transferred resistance is transitory or it can be overwhelmed.