Effects of irradiation on surface carbohydrates of larvae of Schistosoma mansoni

Individually or as a Team-The Immunological Milieu in the Lung Caused by Migrating Single-Sex or Mixed-Sex Larvae of Schistosoma mansoni

While the lung is considered an efficient site for stopping the larvae of the acute Schistosoma spp. infection phase from migrating through extensive inflammatory responses in the surrounding tissues, little is known about these processes. To date, the highest resistance to infection has been achieved in experimental studies with radiation-attenuated cercariae immunization, which elicits a strong Th1/Th2 response in the lung and results in up to 80% protection. Based on our own studies demonstrating a systemic, unpolarized Th1/Th2 response resulting from infection with male or female Schistosoma mansoni, we hypothesize that this atypical immune response is already detectable during the pulmonary passage of parasite larvae. Therefore, we examined the immune milieu in the lungs of mice caused by migrating schistosome larvae, either male or female (single-sex groups) or male + female (bisexual control), 4 and 16 days after infection in bronchoalveolar lavage and lung tissue by flow cytometry, qPCR, and multiplex analyzes. Our results show only minor differences in the inflammatory profile between the single-sex groups but significant differences compared with the bisexual control group. Both single-sex infected groups have increased expression of inflammatory markers in lung tissue, higher numbers of cytotoxic T cells (day 4 post-infection) and more T helper cells (day 16 post-infection), compared with the bisexual control group. A single-sex infection, regardless of whether it is an infection with male or female cercariae, causes an immune milieu in the lung that is clearly different from an infection with both sexes. In terms of identifying therapeutic targets to achieve resistance to re-infection, it is of great scientific interest to identify the differences in the inflammatory potential of male or female and male + female parasites.

Ultraviolet disinfection of Schistosoma mansoni cercariae in water

BACKGROUND

Schistosomiasis is a parasitic disease that is transmitted by skin contact with waterborne schistosome cercariae. Mass drug administration with praziquantel is an effective control method, but it cannot prevent reinfection if contact with cercariae infested water continues. Providing safe water for contact activities such as laundry and bathing can help to reduce transmission. In this study we examine the direct effect of UV light on Schistosoma mansoni cercariae using ultraviolet light-emitting diodes (UV LEDs) and a low-pressure (LP) mercury arc discharge lamp.

METHODOLOGY

S. mansoni cercariae were exposed to UV light at four peak wavelengths: 255 nm, 265 nm, 285 nm (UV LEDs), and 253.7 nm (LP lamp) using bench scale collimated beam apparatus. The UV fluence ranged from 0-300 mJ/cm2 at each wavelength. Cercariae were studied under a stereo-microscope at 0, 60, and 180 minutes post-exposure and the viability of cercariae was determined by assessing their motility and morphology.

CONCLUSION

Very high UV fluences were required to kill S. mansoni cercariae, when compared to most other waterborne pathogens. At 265 nm a fluence of 247 mJ/cm2 (95% confidence interval (CI): 234-261 mJ/cm2) was required to achieve a 1-log10 reduction at 0 minutes post-exposure. Cercariae were visibly damaged at lower fluences, and the log reduction increased with time post-exposure at all wavelengths. Fluences of 127 mJ/cm2 (95% CI: 111-146 mJ/cm2) and 99 mJ/cm2 (95% CI: 85-113 mJ/cm2) were required to achieve a 1-log10 reduction at 60 and 180 minutes post-exposure at 265 nm. At 0 minutes post-exposure 285 nm was slightly less effective, but there was no statistical difference between 265 nm and 285 nm after 60 minutes. The least effective wavelengths were 255 nm and 253.7 nm. Due to the high fluences required, UV disinfection is unlikely to be an energy- or cost-efficient water treatment method against schistosome cercariae when compared to other methods such as chlorination, unless it can be demonstrated that UV-damaged cercariae are non-infective using alternative assay methods or there are improvements in UV LED technology.

Schistosomes in the Lung: Immunobiology and Opportunity

Schistosome infection is a major cause of global morbidity, particularly in sub-Saharan Africa. However, there is no effective vaccine for this major neglected tropical disease, and re-infection routinely occurs after chemotherapeutic treatment. Following invasion through the skin, larval schistosomula enter the circulatory system and migrate through the lung before maturing to adulthood in the mesenteric or urogenital vasculature. Eggs released from adult worms can become trapped in various tissues, with resultant inflammatory responses leading to hepato-splenic, intestinal, or urogenital disease – processes that have been extensively studied in recent years. In contrast, although lung pathology can occur in both the acute and chronic phases of schistosomiasis, the mechanisms underlying pulmonary disease are particularly poorly understood. In chronic infection, egg-mediated fibrosis and vascular destruction can lead to the formation of portosystemic shunts through which eggs can embolise to the lungs, where they can trigger granulomatous disease. Acute schistosomiasis, or Katayama syndrome, which is primarily evident in non-endemic individuals, occurs during pulmonary larval migration, maturation, and initial egg-production, often involving fever and a cough with an accompanying immune cell infiltrate into the lung. Importantly, lung migrating larvae are not just a cause of inflammation and pathology but are a key target for future vaccine design. However, vaccine efforts are hindered by a limited understanding of what constitutes a protective immune response to larvae. In this review, we explore the current understanding of pulmonary immune responses and inflammatory pathology in schistosomiasis, highlighting important unanswered questions and areas for future research.

Why the radiation-attenuated cercarial immunization studies failed to guide the road for an effective schistosomiasis vaccine: A review

Schistosomiasis is a debilitating parasitic disease caused by platyhelminthes of the genus Schistosoma, notably Schistosoma mansoni, Schistosoma haematobium, and Schistosoma japonicum. Pioneer researchers used radiation-attenuated (RA) schistosome larvae to immunize laboratory rodent and non-human primate hosts. Significant and reproducible reduction in challenge worm burden varying from 30% to 90% was achieved, providing a sound proof that vaccination against this infection is feasible. Extensive histopathological, tissue mincing and incubation, autoradiographic tracking, parasitological, and immunological studies led to defining conditions and settings for achieving optimal protection and delineating the resistance underlying mechanisms. The present review aims to summarize these findings and draw the lessons that should have guided the development of an effective schistosomiasis vaccine.

Immunity induced by the radiation-attenuated schistosome vaccine

As a paradigm for the development of a vaccine against human schistosomiasis, the radiation-attenuated (RA) vaccine has enabled the dissection of different immune responses as putative effector mechanisms. This review considers advances made in the past, and updates our knowledge with reference to recent studies that have provided new information relevant particularly to the early innate events after vaccination, and to the nature of the protective effector mechanism. Priming of a protective response by RA larvae is a highly co-ordinated series of events starting in the skin, draining lymph nodes and lungs, leading to the development of various effector responses, ranging from Th1-associated cell-mediated activity, to anti-parasitic antibodies, all of which contribute to the elimination of challenge larvae to varying extents. In this respect, the RA vaccine elicits a multifaceted immune response, from which we can derive valuable insights relevant to the future design of novel delivery systems and adjuvants for recombinant and subunit vaccines.

Characterization of a stage-specific Mr16000 schistosomular surface glycoprotein antigen of Schistosoma mansoni

A 16 kDa Schistosoma mansoni schistosomular surface antigen (Sm16) was originally described as the target of a passively protective mAb (B3A). It appeared on the schistosomular surface after transformation of cercariae and was uniquely recognised by sera from animals exposed to attenuated cercariae. In this work sequential extractions of schistosomula with Triton X-114 and sodium dodecyl sulphate showed Sm16 to be an integral membrane structure which did not appear to be glycosylphosphatidylinositol-anchored as judged by experiments using phosphatidyl inositol-specific phospholipase C. The antigen was strongly reactive in Western blotting with rabbit irradiated vaccine sera. Sm16 was demonstrated in the hepatopancreas of S. mansoni-infected snails and was equally abundant in cercariae and mechanically- transformed schistosomula but was undetected in liver stage worms or eggs. Immunoelectron microscopy showed Sm16 to be localised, in cercariae, to what are believed to be subtegumental cell bodies packed with membraneous vesicles. Treatment with proteases and with sodium metaperiodate showed Sm16 to be a glycoprotein of which the epitope recognised by B3A was periodate sensitive. Two-dimensional electrophoresis gave a PI of 6. Neither the size or the recognition by B3A was affected by treatment with N-glycosidase F, endoglycosidase F or endo-alpha-N-acetylgalactosaminidase. Western blotting using a wide range of biotinylated lectins showed recognition only by peanut agglutinin and Ricinus communis agglutinin II (ricin). It is concluded that Sm16 has antigenic surface-exposed O-linked complex oligosaccharides which lack mannose/glucose, GlcNAc, L-fucose and sialic acid but contain terminal Gal beta (1-3) GalNAc and/or galactose.

Production of murine monoclonal antibodies to guinea pig leukocytes and immunohistochemistry of guinea pig skin exposed to Schistosoma mansoni

Using histochemical ATPase-staining of the guinea pig epidermal sheet, we have demonstrated remarkable accumulations of ATPase-positive cells after exposure to attenuated Schistosoma mansoni cercariae. To characterize further the cells accumulating in the skin after exposure to S. mansoni, we produced a panel of monoclonal antibodies (MAb) to guinea pig leukocytes. These were immunohistochemically classified into 15 types and included MAb to the major histocompatibility complex (MHC) Class I and Class II molecules, shared antigens of all lymph node cells or between lymph node cells and Langerhans' cells (LC), T cells and macrophages (M phi), and M phi including the large Tingible body M phi in the secondary follicle. Varied MAb to M phi, including commercially available MAb (MR-1), were negative with ATPase- and MHC Class II-positive cells accumulated in the skin exposed to S. mansoni. Three MAb (HUSM-30 and 46, and commercially available MSgp2) detected an identical staining profile of accumulated cells with epidermal LC, but two MAb (HUSM-12 and 42) positively stained accumulated cells but not resident LC. These results indicate that the cells accumulated in the guinea pig skin within a few days after exposure to attenuated cercariae of S. mansoni are closest to LC, not to Mø, and may be blood-borne LC/dendritic cells.