Tissue responses exhibited by Biomphalaria alexandrina snails from different Egyptian localities following Schistosoma mansoni exposure

Snails’ susceptibilities to infection with Schistosoma mansoni were determined through observation of infection rates, total cercarial production and tissue responses of the first generation (F1) of Biomphalaria alexandrina snails, originally collected from different Egyptian governorates (Giza, Fayoum, Kafr El-Sheikh, Ismailia and Damietta) and responses were compared between groups. The emergence of cercariae for a 3-month period and the calculation of survival and infection rates, in control (Schistosome Biological Supply Center; SBSC) and infected snails were evaluated. SBSC and Giza snails showed greater susceptibilities to infection and lower mortality rates. In addition, at 6 and 72 h post-exposure to miracidia all the snail groups showed no difference in the anatomical locations of sporocysts. The larvae were found in the head-foot, the mantle collar and the tentacles of the snails. Sporocysts showed normal development with low tissue reactions in SBSC and Giza snail groups infected with S. mansoni miracidia (SBSC). However, in Fayoum, Kafr El-Sheikh, Ismailia and Damietta snail groups, variable tissue responses were observed in which numerous hemocytes made direct contact with S. mansoni larvae forming capsules. The results suggested that, different responses of B. alexandrina snail’s hemocytes towards S. mansoni are related to the degree of susceptibility of these snails. So this is important in planning the strategy of schistosomiasis control.     

Transstadial immune activation in a mosquito: Adults that emerge from infected larvae have stronger antibacterial activity in their hemocoel yet increased susceptibility to malaria infection

Larval and adult mosquitoes mount immune responses against pathogens that invade their hemocoel. Although it has been suggested that a correlation exists between immune processes across insect life stages, the influence that an infection in the hemocoel of a larva has on the immune system of the eclosed adult remains unknown. Here, we used Anopheles gambiae to test whether a larval infection influences the adult response to a subsequent bacterial or malaria parasite infection. We found that for both female and male mosquitoes, a larval infection enhances the efficiency of bacterial clearance following a secondary infection in the hemocoel of adults. The adults that emerge from infected larvae have more hemocytes than adults that emerge from naive or injured larvae, and individual hemocytes have greater phagocytic activity. Furthermore, mRNA abundance of immune genes—such as cecropin A, Lysozyme C1, Stat‐A, and Tep1—is higher in adults that emerge from infected larvae. A larval infection, however, does not have a meaningful effect on the probability that female adults will survive a systemic bacterial infection, and increases the susceptibility of females to Plasmodium yoelii, as measured by oocyst prevalence and intensity in the midgut. Finally, immune proficiency varies by sex; females exhibit increased bacterial killing, have twice as many hemocytes, and more highly express immune genes. Together, these results show that a larval hemocoelic infection induces transstadial immune activation—possibly via transstadial immune priming—but that it confers both costs and benefits to the emerged adults.     

Schistosoma mansoni in Susceptible and Resistant Snail Strains Biomphalaria tenagophila: In Vivo Tissue Response and In Vitro Hemocyte Interactions

Schistosomiasis is a parasitic disease that is highly prevalent, especially in developing countries. Biomphalaria tenagophila is an important invertebrate host of Schistosoma mansoni in Brazil, with some strains (e.g. Cabo Frio) being highly susceptible to the parasite, whereas others (e.g. Taim) are completely resistant to infection. Therefore, B. tenagophila is an important research model for studying immune defense mechanisms against S. mansoni. The internal defense system (IDS) of the snail comprises hemocytes and hemolymph factors acting together to recognize self from non-self molecular patterns to eliminate the threat of infection. We performed experiments to understand the cellular defenses related to the resistance and/or susceptibility of B. tenagophila to S. mansoni. During the early stages of infection, fibrous host cells of both snail strains were arranged as a thin layer surrounding the sporocysts. However, at later stages of infection, the cellular reactions in resistant snails were increasingly more intense, with thicker layers surrounding the parasites, in contrast to susceptible strains. All parasites were damaged or destroyed inside resistant snails after 10 h of infection. By contrast, parasites inside susceptible snails appeared to be morphologically healthy. We also performed experiments using isolated hemocytes from the two strains interacting with sporocysts. Hemocyte attachment started as early as 1 h after initial infection in both strains, but the killing of sporocysts was exclusive to hemocytes from the resistant strain and was time course dependent. The resistant strain was able to kill all sporocysts. In conclusion, our study revealed important aspects of the initial process of infection related to immune defense responses of strains of B. tenagophila that were resistant to S. mansoni compared with strains that were susceptible. Such information is relevant for the survival or death of the parasites and so is important in the development of control measures against this parasite.     

Biomphalaria glabrata (Gastropoda): effect of urethane on the morphology and function of hemocytes, and on susceptibility to Schistosoma mansoni (Trematoda)

Urethane (ethyl carbamate) anesthesia of Biomphalaria glabrata resulted in several rapid changes to the snail's blood picture. At 2 hr postexposure (PE) to the drug, there was an elevation in the prevalence of acid phosphatase (APase)-positive hemocytes, a significant increase in the number of APase granules per cell, a three fold increase in circulating blood cell number, and a decrease in the percentage of hemocytes expressing a cell subpopulation-specific surface membrane epitope (BGH₁). However, urethane had little effect on erythrophagocytosis by host hemocytes. All of the observed changes returned to control levels by 12 hr PE to the drug. Blood cells cultured with various concentrations of the anesthetic in vitro did not exhibit any alterations in the parameters described above. Since circulating hemocytes represent the primary effector component involved in internal defense reactions, the effect of urethane-induced changes in the composition of circulating blood cells on susceptibility to a larval trematode, Schistosoma mansoni, was examined. Such changes had no apparent effect on host susceptibility since the rate of infection for urethane-exposed snails (88.2%) was the same as for nonurethane-treated B. glabrata (82.4%). However, the effects of urethane-induced changes in hemocyte number and composition on other invading organisms is not known. Therefore, it is suggested that such alterations should be considered when internal defense reactions are studied in snails exposed to this drug and other commonly used anesthetics.     

N-Glycosylation patterns of hemolymph glycoproteins from Biomphalaria glabrata strains expressing different susceptibility to Schistosoma mansoni infection

Comparative analyses of the N-glycosylation pattern of hemolymph glycoproteins from Biomphalaria glabrata strains Puerto Rico (BgPR) and Salvador (BgBS-90), differing in their susceptibility towards Schistosoma mansoni infection, were performed by Western blotting, enzyme-linked immunosorbent assays, two-dimensional high-performance liquid chromatography and mass spectrometry. Obtained data demonstrated an enhanced expression of serologically cross-reacting, fucosylated carbohydrate epitopes by the highly susceptible BgPR-strain in comparison to the resistant BgBS-90-strain. In particular, glycoproteins of BgPR snails exhibited larger amounts of glycans with (β1-2)-linked xylose or terminal Fuc(α1-3)GalNAc(β1-4)[±Fuc(α1-3)]GlcNAc(β1-)-units which are known to mediate cross-reactivity with schistosomal glycoconjugates. This finding could be corroborated by immunohistochemical studies showing again an enhanced expression of such carbohydrate epitopes in BgPR tissue. Hence, our results provide evidence for a correlation of B. glabrata susceptibility towards S. mansoni infection and the expression of carbohydrate determinants shared by the parasite and its intermediate host.     

Concanavalin A-induced receptor redistribution on Biomphalaria glabrata hemocytes: Characterization of capping and patching responses

Exposure of rounded, glass-adherent hemocytes from a Schistosoma mansoni-susceptible (PR albino) and S. mansoni-refractory (10-R2) stock of snails, Biomphalaria glabrata, to fluoresceinlabeled concanavalin A induces a redistribution of surface membrane Con A receptors. Receptor redistribution (patching and capping) on hemocytes from both snail stocks can be characterized as (1) rapid, with maximum cap formation occurring within 15 min of lectin treatment at 22°C, (2) sodium azide sensitive, but only at relatively high inhibitor concentrations (100–200 mm^?N₃ for capping and 200 mm^?N₃ for patching inhibition), (3) pronase sensitive (partial), but trypsin resistant, and (4) generally unaffected by exposure of snails to S. mansoni miracidia 60 or 180 min prior to extraction of hemolymph (hemocyte) samples for Con A testing. Although differences in the time course of receptor redistribution are exhibited between PR albino and 10-R2 snail hemocytes, the results of experiments involving sodium azide, proteolytic enzymes, and schistosome exposure strongly suggest that Con A-binding determinants and their associated membrane components on rounded hemocytes are very similar in both susceptible and refractory Biomphalaria stocks. It is concluded that if schistosome recognition in refractory 10-R2 snails is mediated through specific hemocyte membrane components, those components associated with Con A reactivity probably are not directly involved in the recognition process.     

Schistosoma mansoni: Cytotoxicity of hemocytes from susceptible snail hosts for sporocysts in plasma from resistant Biomphalaria glabrata

Sporocysts of Schistosoma mansoni (PR1 strain) survive and grow in Biomphalaria glabrata PR albino strain snails, whereas they are encapsulated and die in B. glabrata 10R2 strain snails. These processes also occur in an in vitro system in which the only living cells are those of sporocysts and snail hemolymph. Hemocytes of the susceptible snail are normally not effective in damaging sporocysts. However, when the encounter occurred in the presence of cell-free plasma from resistant snails, previously impotent hemocytes severely damaged sporocysts in 24 hr. The cytotoxic capacity of resistant strain hemocytes was not altered by plasma from susceptible snails. Furthermore, it was retained even when plasma was replaced by culture medium free of snail components. The nature of the plasma factor(s) which facilitated damage by otherwise impotent hemocytes is discussed, and evidence is evaluated for the hypothesis that snail resistance is dependent upon the specificity of cytophilic factors present both in the plasma and on the hemocyte plasma membranes.     

Manganese superoxide dismutase from Biomphalaria glabrata

The investigation of the response of Biomphalaria glabrata snails to Echinostoma paraensei (digenea) at 2 days post-exposure by suppression subtractive hybridization yielded a partial sequence of the anti-oxidant enzyme manganese superoxide dismutase (MnSOD). Full-length MnSOD (669nt) from M line and BS-90 strains of B. glabrata differed by one synonymous nucleotide replacement. B. glabrata has 1-4 MnSOD loci (Southern hybridization). Both snail strains expressed MnSOD at equal baseline levels (quantitative PCR). Susceptible snails increased expression of MnSOD following infection with E. paraensei or Schistosoma mansoni, and expression was reduced in the incompatible combination (BS-90 B. glabrata and S. mansoni). Thus, MnSOD did not determine resistance or susceptibility for these parasites, but expression of MnSOD is consistent with its involvement in a stress response of B. glabrata.     

Studies on resistance in snails: Interference by nonirradiated echinostome larvae with natural resistance to Schistosoma mansoni in Biomphalaria glabrata

Most of the genetically selected juvenile Biomphalaria glabrata snails, normally strongly resistant to Schistosoma mansoni, lost their juvenile resistance to this parasite when other trematodes were concurrently present in the snail. Three echinostome species all were able to reduce this genetically controlled juvenile resistance: Echinostoma lindoense, E. paraensei, and e. liei. Subsequently, adult resistance to S. mansoni, clearly present in control snails of the same age and strain that were not doubly infected, failed to develop in most of the snails that also harbored echinostomes. Other snails, selected for resistance as adults to S. mansoni, also usually became susceptible to this parasite following infection with E. paraensei. The capacity of E. paraensei to interfere with the snails' resistance to S. mansoni was greater than that of E. lindoense. Destruction by predation of primary sporocysts of S. mansoni by echinostome rediae prevented completion of development of the S. mansoni infections. In a number of snails all primary S. mansoni sporocysts were consumed before secondary sporocysts could be formed. In most experimental snails, however, some of the schistosomes survived, often as a small number of degenerated secondary S. mansoni sporocysts. The capability of flukes to interfere with the natural defense of snails may be an important phenomenon whereby trematode species survive in their snail hosts.     

Host life history and the effect of parasitic castration on growth: A field study of Cerithidea californica Haldeman (Gastropoda : Prosobranchia) and its trematode parasites

The prevalence of parasitic infection by larval digenetic trematodes in natural populations of the mud snail, Cerithidea californica Haldeman, was found to increase with snail length; all snails ≥ 33 mm were infected. Distributions of infections by the seven most common larval trematodes were heterogeneous due to two species being more common than expected in the smaller size classes of snails, two being more common than expected in the larger size-classes of snails and three species being most prevalent in snails of intermediate length. The relative abundances of trematodes in different size-classes reflected these distributional patterns.A mark-recapture field study of snail growth rates failed to demonstrate that parasitic infection causes gigantism in Cerithidea. Parasitism tended to stunt the growth of juvenile snails and to a lesser degree, that of adult snails. The effects of trematodes on snail growth was shown to be species specific. This finding contrasts with those of earlier studies in which gigantic growth was observed in infected snails. This discrepancy is attributed to differences in the life histories of the host snails. It is predicted that gigantism will occur commonly in short-lived or semelparous species of snails but rarely, if ever, in long-lived iteroparous species which are predominately marine.     

Physiological functions of hemocytes newly emerged from the cultured hematopoietic organs in the silkworm, Bombyx mori

Abstract  Cellular immunity is a very important part of insect innate immunity. It is not clear if hemocytes entering the hemolymph require a maturation process to become competent. The establishment of a tissue culture system for the insect hematopoietic organs would enable physiological function assays with hemocytes newly emerged from hematopoietic organs. To this end, we established a hematopoietic organ culture system for the purebred silkworm pnd pS and then studied the physiological functions of the newly emerged hemocytes. We found that Grace's medium supplemented with 10% heated silkworm larval plasma was better for culturing the hematopoietic organs of pnd pS . Newly emerged hemocytes phagocytosed propidium iodide-labeled bacteria and encapsulated the Iml-2 coated nickel beads as well as pupal tissue debris. This culture system is therefore capable of generating physiologically functional hemocytes. These hemocytes can be used to study the mechanisms of the hemocyte immune response among others.     

An overview of surface specializations in the digenetic trematodes

The outer covering of digenetic trematodes undergoes a number of changes in the course of the life cycle in adaptation to parasitism and to the host-seeking requirements of the various stages. Using Schistosoma mansoni as a model, I review morphological, physiological, and cytochemical features of the coverings of miracidia, sporocysts, cercariae, and adults. Such features should be used with caution in evaluating phylogenetic relationships of any flatworms since the environment is itself a powerful determinant.     

Schistosome sporocyst-killing Amoebae isolated from Biomphalaria glabrata.

Explants and swabs from the pericardium and mantle of three strains of Biomphalaria glabrata, two of them resistant to infection with Schistosoma mansoni, have yielded small amoebae, 3–5μm in diameter, in culture. These amoebae have been grown axenically through > 50 passages to date. The amoebae form cysts in dense cultures. When mixed with S. mansoni mother sporocysts in vitro, the amoebae adhere to and kill the trematodes within several hours. For 1–2 days thereafter, the amoebae proliferate rapidly at a generation time of about 5 hr, then return to normal growth. Sonically disrupted sporocysts also induce proliferation. Live sporocysts do not attract the amoebae or emit soluble substances which influence amoebal growth. Amoebae also adhered to and killed S. mansoni daughter sporocysts and cells derived from B. glabrata embryos; however, they did not harm S. mansoni cercariae or rediae of other trematode species. The proportion of mantle explants yielding amoebae was significantly higher (P<0.05) in one of the resistant snail strains than in the susceptible strain; however, whether amoebae contribute to snail resistance is unknown. Exposure of snails to S. mansoni miracidia did not influence the proportion of snails yielding amoebae.     

Dynamics of the leukocytic response of Biomphalaria glabrata during the larval development of Schistosoma mansoni and Echinostoma liei

The daily evolution of the number of hemocytes in Biomphalaria glabrata was ascertained under three conditions: uninfected snails, snails infected with Schistosoma mansoni, and snails infected with Echinostoma liei. The Results show differences between the three experiments as well as in the average hemocyte density over the whole experimental period, as in the temporal dynamics of circulating hemocyte number. Specifically, it appears that the development of E. liei in B. glabrata induces a density of circulating hemocytes greater than that in uninfected B. glabrata or in snails infected with S. mansoni. The hemocyte dynamics observed in both experimental groups might best be interpreted by taking into account differences in the immunogenic stimulating capacity of the two trematodes and different physiological functions of the hemocytes brought into play during the infection: wound repair, nutrient digestion and transport, and excretion.     

Sex,snails, and schistosomes: the influence of compatibility genotype on reproductive strategy

Summary

The impact of current parasitic infection status on mate choice and reproductive strategies has been widely reported, particularly amongst vertebrate host-parasite systems. However, evidence is lacking as to whether animals discriminate between mates on the basis of their potential infection status, in terms of host resistance or susceptibility genotype (i.e., compatibility). In a series of experiments, Biomphalaria glabrata snail strains were artificially selected for either resistance or susceptibility to Schistosoma mansoni infection. Individual snails from each line were then paired with a partner of matched compatibility status and the proportion of outcrossed to selfed offspring produced identified by RAPD-PCR. Individual unselected snails, either infected or uninfected, were then given a choice of partners artificially selected for either resistance or susceptibility to infection, and their behaviour analysed. The results demonstrate that compatibility genotype can influence reproductive strategy and are discussed in terms of their implications regarding the maintenance of sex and the evolution of recognition systems.     

Potamopyrgus antipodarum(Mollusca:Hydrobiidae) in continental aquatic gastropod communities: impact of salinity and trematode parasitism

The structure of gastropod communities was examined from January to June 1999 in four sites of the streams of Mont Saint-Michel Bay along a gradient of salinity, and the occurrence of larval trematodes infecting snails was studied. Abundance and species richness of gastropods increased from polyhaline (95 snails, 1 species) to oligohaline waters (6672 snails, 6 species). Whatever the salinity, the most abundant species was Potamopyrgus antipodarum, an invasive non-indigenous species that represented 80% of the gastropods. Only one male was found in P. antipodarum populations suggesting a predominantly parthenogenetic mode of reproduction. Among 7218 gastropods collected, 1.2% were infected by larval trematodes: 5 species in Lymnaea peregra (4.4%), 4 species in Planorbis planorbis (12.0%), one echinostome in Physa acuta (0.2%), and a new species of Sanguinicola in P. antipodarum (0.5%). This is the first record of infected P. antipodarum in Europe. No parasites were found in polyhaline waters. The prevalence per host population varied from 0 to 100% depending on time of collection, salinity and host species. In the lowest-salinity site, abundance of gastropods and prevalence of trematodes were negatively correlated. The dominance of P. antipodarum in the gastropod communities is discussed in relation with euryhalinity, parthenogenesis and weak rate of parasitism.