Recombinant human interleukin-1-mediated killing of Schistosoma mansoni primary sporocysts in Biomphalaria glabrata.

Previous work has indicated that injection of recombinant-human interleukin (rhIL)-1beta in Schistosoma mansoni-infected M-line Biomphalaria glabrata resulted in a significant reduction in the number of cercariae shed. The purpose of the present work was to determine if primary sporocysts were killed following rhIL-1beta injection in susceptible snails and, if so, to determine if killing was the direct result of hemocyte activity. Counting of primary sporocysts indicated a 50% reduction in the number surviving at 3 days PE in snails from 2 susceptible strains following injection. Histological analysis indicated that killing occurred with little-to-no observable hemocyte/parasite contact, whereas short-term culture of primary sporocysts with cell-free plasma (hemolymph) from injected snails rapidly initiated killing in vitro. Because levels of a snail IL-1-like molecule (SnaIL-1) drop significantly following schistosome exposure in M-line snails, because resistant snails maintain higher SnaIL-1 levels following infection, and because rhIL-1beta upregulates hemocyte cytotoxic mechanisms, these data support the contention that SnaIL-1 plays a role in determining resistance in B. glabrata. These data also indicate that schistosome death may be separated from parasite encapsulation by hemocytes and that an as yet unidentified humoral killing mechanism/factor may exist in B. glabrata. Lastly, these data further support the hypothesis that cytokine-like molecules are important, functionally conserved immunodefense mediators in both vertebrates and invertebrates.

Schistosoma mansoni: interleukin-1 increases phagocytosis and superoxide production by hemocytes and decreases output of cercariae in schistosome-susceptible Biomphalaria glabrata.

Decreases in the number of Schistosoma mansoni cercariae released from susceptible M-line Biomphalaria glabrata were detected following injection with the recombinant human cytokine, interleukin-1. No differences in either the time post-exposure at which shedding began or the percentage of snails shedding cercariae were detected between interleukin-1 injected, heat-inactivated interleukin-1 injected, or sham injected controls. However, sham injected and heat-inactivated interleukin-1 injected snails maintained significantly higher (approximately three-fold) levels of cercarial production compared to interleukin-1 injected snails over 8 weeks of cercarial shedding. Injection of interleukin-1 into schistosome-susceptible (M-line) and resistant (13-16-R1) strains of B. glabrata increased hemocyte phagocytosis of target particles and phagocytosis stimulated O2- production in both snail strains at 24 hr postexposure to the parasite. Resistant 13-16-R1 snails maintained, on average, 2.4 times the number of O2- producing phagocytic cells than did M-line susceptible snails, indicating that the incomplete abrogation of cercarial shedding in M-line snails may be due to an inadequate number of activated circulating effector cells in these snails. These data strongly support the contention that the evolutionarily conserved cytokine, interleukin-1, or a molecule in snail plasma with interleukin-1-like immunospecificity, biological activity, and function plays a significant role in the maintenance of susceptibility or resistance to S. mansoni infection in B. glabrata. Finally, these data also supply evidence for the evolutionary conservation of the function and role of interleukin-1, O2-, and antioxidant defense mechanisms in this host-parasite relationship.

Interleukin 1 activity in haemolymph from strains of the snail Biomphalaria glabrata varying in susceptibility to the human blood fluke, Schistosoma mansoni: presence, differential expression, and biological function.

Cytokines control many of the steps in the complex pathways of immune and inflammatory responses in mammals. Recent reports also indicate that some invertebrates may produce cytokines such as interleukin 1 (IL-1). Certain strains of the snail, Biomphalaria glabrata (intermediate host for the human blood fluke, Schistosoma mansoni), possess a soluble plasma factor that stimulates the haemocyte-mediated killing of larval schistosomes, making them resistant to infection. In this study, we have sought to determine whether these snails possessed IL-1 in their plasma, and whether this cytokine was associated with resistance of B. glabrata to S. mansoni. Plasma from susceptible (M-line) and resistant (10-R2, 13-16-R1) strains of B. glabrata that had been unexposed or exposed to S. mansoni were tested for the presence of IL-1-like activity. Experiments employing both a bioassay and an immunoassay indicated that an IL-1-like molecule was present, in varying quantities, among the snail strains. Further, plasma IL-1 levels were significantly affected by exposure to S. mansoni, with levels dropping in M-line and 10-R2 snails, but increasing in the 13-16-R1 strain. However, both resistant strains maintained significantly higher IL-1 levels than M-line snails. Recombinant, human IL-1 (rhIL-1) was shown to prime haemocytes from both resistant snail strains for superoxide production, but had no effect on haemocytes from susceptible B. glabrata. Moreover, the addition of an IL-1 receptor antagonist protein (IRAP) eliminated this priming effect. Priming with rhIL-1 and/or IRAP had no effect on phagocytosis rates in any of the snail strains tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Plagiorhynchus cylindraceus (Acanthocephala) on the energy metabolism of adult starlings, Sturnus vulgaris.

Although the relationship between intestinal parasitism, the ingestion and use of energy, and host survival is expected, little work has been done to outline the effect of such organisms upon their host's nutritional requirements in an ecological context. This study is the first to demonstrate that an intestinal helminth previously reported to be of little or no histopathological consequence, Plagiorhynchus cylindraceus, has a significant detrimental impact upon the flow of food energy through a definitive host, the European starling, Sturnus vulgaris. Within both male and female adult European starlings reductions in standard metabolic rates occurred as the result of initial infection, indicating that the host's basal metabolism/thermal regulatory abilities were altered. Moreover, initially infected male starlings, but not females, had an increased consumption and excretion of energy and maintained lower average daily body weights versus controls when temperature stressed. These results appear to be due to either a parasite-mediated alteration in host activity and/or to the disruption of host-digestive abilities. Additionally, these data indicate that, overall, male and female S. vulgaris respond differently to infection and that intestinal helminths normally thought to be of little or no pathological consequence to the host are factors that should be addressed in future studies regarding animal energetics, ecology, and behaviour.

Identification of a Schistosoma mansoni sporocyst excretory-secretory antioxidant molecule and its effect on superoxide production by Biomphalaria glabrata hemocytes.

Excretory-secretory (E-S) products obtained during in vitro Schistosoma mansoni miracidium-to-sporocyst transformation were found to contain a 108-kDa polypeptide capable of scavenging both exogenously produced and M-line Biomphalaria glabrata hemocyte-derived superoxide (O2-) anions. Separation of crude transformation E-S products using HPLC and ion exchange chromatography resulted in the separation of two isoforms of the 108-kDa molecule. Using an in vitro phagocytosis assay, both isoforms were found to be capable of reducing O2- production by phagocytically stimulated M-line B. glabrata hemocytes without cell loss and without a concomitant reduction in phagocytosis. Although parasite antioxidant molecules appear to play a role in the evasion of host oxidative defense systems in several parasite-vertebrate systems, no previous reports of a parasite antioxidant capability against the potential of oxidative killing by invertebrate defense systems has been reported. In conjunction with the previously confirmed production of O2- by B. glabrata hemocytes and reports of reactive oxygen metabolite production by hemocytes from several molluscan species, these results indicate that reactive forms of oxygen and parasite antioxidant systems may play an important role in the determination of compatibility in the trematode-mollusc relationship.

Isolation and functional characterization of snail hemocyte-modulating polypeptide from primary sporocysts of Schistosoma mansoni.

Infection with larval trematodes has been shown to inhibit several snail-host defences, including hemocyte phagocytosis, cytotoxicity, motility, and adherence. Certain plasma factors which mediate snail defence responses, and which may be produced by host hemocytes, also appear to be altered by these parasites. In this study we present protocols for the isolation of 2 proteins from larval Schistosoma mansoni excretory-secretory (ES) products and detail the effects of these components on Biomphalaria glabrata hemocyte protein synthetic/secretory (S/S) activity. Schistosome ES proteins, separated with a combination of membrane ultrafiltration, size exclusion, and ion exchange chromatography, were tested for their in vitro effect on cultured snail hemocytes, in the presence and absence of homologous plasma. A high-molecular-weight ultrafiltration fraction of parasite ES products (H30), in combination with plasma, was found to differentially affect susceptible (M-line) and resistant (10-R2) snail hemocytes. Secretion of metabolically labeled polypeptides by M-line cells was inhibited significantly while the S/S response of 10-R2 hemocyte polypeptides was not affected. In the absence of homologous plasma, little or no differential affect of ES polypeptides on hemocyte S/S activity was seen. Much of the inhibitory activity of H30 was attributable to a partially purified fraction, Peak I (PkI), of ES products. Evidence suggests that, in its native state, PkI is a high-molecular-weight protein aggregate comprising subunits of approximately 22-24 kDa. Thus, PkI, in the presence of homologous plasma components, is a potential mediator of schistosome-induced suppression of polypeptide synthesis or secretion in hemocytes of susceptible snails. In combination with other parasite and host factors, PkI may be involved in the host-parasite interaction which leads to the state of susceptibility or resistance found in our strains of B. glabrata.

In vitro effect of larval Schistosoma mansoni excretory-secretory products on phagocytosis-stimulated superoxide production in hemocytes from Biomphalaria glabrata.

The in vitro production of the reactive oxygen metabolite superoxide (O2-) was confirmed in hemocytes from the schistosome intermediate host Biomphalaria glabrata. Active forms of the enzyme superoxide dismutase (SOD) inhibited reduction of nitroblue tetrazolium (NBT) to formazan in cells that had phagocytozed zymosan particles, whereas an inactivated form of SOD did not. Moreover, based on the prevalence of O2(-)-positive hemocytes and the relative intensity of NBT staining reactions, hemocytes from the Schistosoma mansoni-resistant 10-R2 strain of B. glabrata possessed an overall greater capacity for generating superoxide than did those from S. mansoni-susceptible M-line snails. Schistosoma mansoni excretory-secretory (E-S) products, released during in vitro transformation of miracidia to sporocysts, inhibited phagocytosis of zymosan particles and superoxide activity in hemocytes from both snail strains, but 10-R2 hemocytes maintained higher levels of phagocytosis and superoxide production than did M-line hemocytes. The dose-dependent decreases in phagocytosis observed in both snail strains in the presence of E-S products could not account fully for the concomitant decrease in superoxide levels detected, indicating that either a single E-S factor differentially affects phagocytosis and superoxide production, or that different E-S factors are involved in the specific interference of each of these hemocyte functions.