Killing of Schistosoma mansoni Sporocysts by Hemocytes from Resistant Biomphalaria glabrata: Role of Reactive Oxygen Species

Abstract

The fate of Schistosoma mansoni (Trematoda) sporocysts in its molluscan host Biomphalaria glabrata (Gastropoda) is determined by circulating phagocytes (hemocytes). When the parasite invades a resistant snail, it is attacked and destroyed by hemocytes, whereas in a susceptible host it remains unaffected. We used 3 inbred strains of B. glabrata: 13-16-R1 and 10-R2, which are resistant to the PR-1 strain of S. mansoni, and M-line Oregon (MO), which is susceptible to PR-1. In an in vitro killing assay using plasma-free hemocytes from these strains, the rate of parasite killing corresponded closely to the rate by which S. mansoni sporocysts are killed in vivo. Hemocytes from resistant snails killed more than 80% of S. mansoni sporocysts within 48 hr, whereas sporocyst mortality in the presence of hemocytes from susceptible snails was <10%. Using this in vitro assay, we assessed the involvement of reactive oxygen species (ROS) produced by resistant hemocytes, during killing of S. mansoni sporocysts. Inhibition of NADPH oxidase significantly reduced sporocyst killing by 13-16-R1 hemocytes, indicating that ROS play an important role in normal killing. Reduction of hydrogen peroxide (H2O2) by including catalase in the killing assay increased parasite viability. Reduction of superoxide (O2-), however, by addition of superoxide dismutase or scavenging of hydroxyl radicals (*OH) and hypochlorous acid (HOCl) by addition of hypotaurine did not alter the rate of sporocyst killing by resistant hemocytes. We conclude that H2O2 is the ROS mainly responsible for killing.

Molecular approach for detecting early prepatent Schistosoma mansoni infection in Biomphalaria alexandrina snail host

“…When resistant snails are exposed to S. mansoni miracidia, haemocytes (snail blood cells) migrate towards the recently transformed sporocysts and enclose them in a multilayered cellular encapsulation. Soon after, the sporocysts are killed by a cytotoxic reaction which most likely involves free radicals such as hydrogen peroxide and/or nitric oxide, in contrast, susceptible snails are not able to successfully defend against S. mansoni larvae and an infection will be developed following miracidial exposure (Hahn et al 2001). Also it may be attributed to the difference in the concentration of schistosomal DNA as regards days of infection (as the infection becomes well established).…”

Control of infection of Biomphalaria alexandrina (Ehrenberg, 1831) with Schistosoma mansoni Sambon, 1907 using Eucalyptus camaldulensis

“…Schistosome infection presents an immune challenge to snails and in response the snails' haemocytes produce reactive oxygen species such as hydrogen peroxide (H 2 O 2 ) to kill the parasite (bayne et al 1980(bayne et al , HaHn et al 2001. Larvae of S. mansoni have their own defence mechanism which involves several antioxidant enzymes such as glutathione-S-transferase, Cu/Zn super oxide dismutase (SOD), glutathione peroxidase and peroxiredoxins (ZelcK & von JanowSKy 2004, wu et al 2009).…”

Regulation of hydrogen peroxide release in circulating hemocytes of the planorbid snail Biomphalaria glabrata

“…When infective S. mansoni larvae penetrate a resistant host, blood cells known as hemocytes form a multilayered cellular encapsulation around the parasite resulting in larval death, usually within 24 hr postinfection [5]. Using an in vitro cellular cytotoxicity assay Hahn et al [1,2] demonstrated that reactive oxygen and nitrogen species, specifically H 2 O 2 and NO, respectively, were responsible for the schistosomicidal activity. Furthermore, it was also shown that selected carbohydrates were capable of triggering B. glabrata hemocyte H 2 O 2 production in vitro [6] suggesting an association between carbohydrate-reactive cell receptors and oxidative/nitrative responses.…”

“…Following S. mansoni penetration of Biomphalaria glabrata, hemocytes of resistant snails migrate towards the parasite, encasing the larva in a multicellular capsule resulting in its destruction via a cytotoxic reaction. Recent studies have revealed the importance of hydrogen peroxide and nitric oxide (H 2 O 2 , NO) in parasite killing [1,2]. It is assumed H 2 O 2 and NO production is tightly regulated although the specific molecules involved remain largely unknown.…”