Further Characterization of Passively Transferred Resistance to Schistosoma mansoni in the Snail Intermediate Host Biomphalaria glabrata

Abstract

A heat-labile plasma factor from genetically resistant 10-R2 Biomphalaria glabrata snails confers passively transferred resistance (PTR) to Schistosoma mansoni when injected into susceptible snails within 24-hr of exposure to miracidia. However, no additional details on PTR have emerged since the initial 1984 report, nor has the plasma resistance factor been characterized. In the present study, new information is provided on the occurrence of resistance factor in plasma of additional types of snails, effect of "priming" resistant plasma donors by prior exposure to miracidia, duration of PTR, molecular weight of resistance factor, and fate of sporocysts in snails with PTR. Susceptible NIH albino snails injected 24 hr prior to exposure to miracidia with individual samples of plasma from a different strain (Salvador B. glabrata) or a different species (B. obstructa) of nonsusceptible snail displayed infection prevalences of 49% or 59% of control levels, respectively, whereas injections of homologous plasma had no effect. PTR was not enhanced by prior exposure of resistant Salvador plasma donors to miracidia. Unexpectedly, PTR induced by injections of Salvador plasma persisted for at least 21 days. The molecular weight of the resistance factor(s) was between 10 and 30 kDa, based on results of centrifugal ultrafiltration. A significantly higher proportion of dead sporocysts occurred in histological sections of tentacles from snails injected with Salvador plasma than in tentacles of snails injected with NIH albino plasma at 7 days postexposure to miracidia. Most dead sporocysts in Salvador plasma-injected snails were undergoing gradual degeneration, rather than rapid, hemocyte-mediated destruction, as occurred in Salvador snails.

Multi-parasite host susceptibility and multi-host parasite infectivity: A new approach of the Biomphalaria glabrata/Schistosoma mansoni compatibility polymorphism

“…The reason of the observed different fates of the nondeveloping MSp (encapsulated vs degenerated) has until now received little attention. The absence of hemocytic reaction around the degenerated MSp strongly suggests unidentified humoral factors responsible for the nondevelopment of these larvae (Sullivan and Richards, 1981;Vasquez and Sullivan, 2001). Such humoral reaction against MSp was always observed in case of immune priming of B. glabrata (Sire el al., 1998;Portela et al, 2013).…”

“…Then, in case of "simultaneous" pluri-miracidial exposure (in our case 8 hours of exposition), not all miracidia penetrate the snail in the same time and we could hypothesize that incompatible miracidia penetrating first and recognized as non-self should be rapidly encapsulated while those penetrating later after this primary hemocyte-mediated defense should be stopped in their development by the presence of toxic plasma molecules and died undergoing gradual degeneration. Physiological unsuitability of the intermediate host was also proposed as a possible factor for the nondevelopment of some MSp (Vasquez and Sullivan, 2001). As emphasized by Basch (1976), compatibility is tested independently for each entering miracidium and each exposed snail.…”

An Overview of Transcriptional Responses of Schistosome-Susceptible (M line) or -Resistant (BS-90) Biomphalaria glabrata Exposed or Not to Schistosoma mansoni Infection

“…Because this ever-expanding list of studies has turned up a long list of factors potentially associated with resistance or susceptibility to infection, we have summarized their results and candidates (see Table S1 ), both to facilitate our own subsequent analyses and also to aid others in gaining a full appreciation of literature involved. Methods of investigation have been diverse, ranging from general responsiveness to infection as measured by the proportion that develop cercariae-producing (patent) infections or by the extent of cellular responses as observed from in vivo or in vitro histological studies ( 50 , 51 ). Circulating snail hemocytes have been extensively compared with respect to numbers or spreading ability ( 22 ), surface markers, enzyme content and expression levels of known immune factors ( 28 , 48 ).…”