Association between cervical dysplasia and female genital schistosomiasis diagnosed by genital PCR in Zambian women

BACKGROUND

Female genital schistosomiasis (FGS) is a neglected tropical gynaecological disease that affects millions of women in sub-Saharan Africa (SSA). FGS is caused by Schistosoma haematobium, a parasitic carcinogen involved in the pathogenesis of squamous cell carcinoma of the bladder. Cervical cancer incidence and mortality are highest in SSA, where pre-cancerous cervical dysplasia is often detected on screening with visual inspection with acetic acid (VIA). There are no studies evaluating the association between VIA positivity and FGS diagnosed by genital PCR.

METHODS

Women were recruited from the Bilharzia and HIV (BILHIV) study in Zambia a community-based study comparing genital self-sampling to provider obtained cervicovaginal-lavage for the diagnosis of FGS in women aged 18-31. FGS was defined as positive Schistosoma DNA from any genital PCR. Urogenital schistosomiasis diagnostics included urine circulating anodic antigen, urine microscopy and portable colposcopy. Participants were offered cervical cancer screening using VIA at Livingstone Central Hospital. Associations of PCR confirmed FGS and other diagnostics with VIA positivity were assessed using multivariable logistic regression.

RESULTS

VIA results were available from 237 BILHIV participants. A positive Schistosoma PCR in any genital specimen was detected in 14 women (5.9%), 28.6% (4/14) of these women had positive VIA compared to 9.0% without PCR evidence of schistosome infection (20/223). Schistosoma PCR positivity in any genital specimen was strongly associated with VIA positivity (OR: 6.08, 95% CI: 1.58-23.37, P = 0.02).

CONCLUSIONS

This is the first study to find an association between FGS and positive VIA, a relationship that may be causal. Further longitudinal studies are needed.

New diagnostic tools in schistosomiasis

Schistosomiasis is a water-based parasitic disease that affects over 250 million people. Control efforts have long been in vain, which is one reason why schistosomiasis is considered a neglected tropical disease. However, since the new millennium, interventions against schistosomiasis are escalating. The initial impetus stems from a 2001 World Health Assembly resolution, urging member states to scale-up deworming of school-aged children with the anthelminthic drug praziquantel. Because praziquantel is safe, efficacious and inexpensive when delivered through the school platform, diagnosis before drug intervention was deemed unnecessary and not cost-effective. Hence, there was little interest in research and development of novel diagnostic tools. With the recent publication of the World Health Organization (WHO) Roadmap to overcome the impact of neglected tropical diseases in 2020, we have entered a new era. Elimination of schistosomiasis has become the buzzword and this has important ramifications for diagnostic tools. Indeed, measuring progress towards the WHO Roadmap and whether local elimination has been achieved requires highly accurate diagnostic assays. Here, we introduce target product profiles for diagnostic tools that are required for different stages of a schistosomiasis control programme. We provide an update of the latest developments in schistosomiasis diagnosis, including microscopic techniques, rapid diagnostic tests for antigen detection, polymerase chain reaction (PCR) assays and proxy markers for morbidity assessments. Particular emphasis is placed on challenges and solutions for new technologies to enter clinical practice.

Application of a circulating-cathodic-antigen (CCA) strip test and real-time PCR, in comparison with microscopy, for the detection of Schistosoma haematobium in urine samples from Ghana

In the detection of parasitic infection, the traditional methods based on microscopy often have low sensitivity and/or specificity compared with the newer, molecular tests. An assay based on real-time PCR and a reagent strip test for detecting circulating cathodic antigen (CCA) have both now been compared with urine filtration and microscopy, in the detection of Schistosoma haematobium infections. Urine samples, obtained from 74 'cases' in areas of Ghana with endemic S. haematobium and 79 'controls' from non-endemic areas, were each checked using the three methods. With the results of the filtration and microscopy taken as the 'gold standard', real-time PCR was found to be 100% specific and 89% sensitive whereas the CCA strips were 91% specific and 41% sensitive. With the samples found to contain > or =50 eggs/10 ml (indicating relatively intense infections), the sensitivities of the PCR and CCA were higher, at 100% and 62%, respectively. As expected, egg counts were negatively correlated with the number of amplification cycles needed, in the PCR, to give a signal that exceeded the background (r=-0.38; P<0.01). Although the real-time PCR and CCA strip tests are very different, both show promise in the detection of S. haematobium infections. The PCR has optimal specificity and high sensitivity but the specificity of the CCA strips and the sensitivity of both tools could still be improved. A more thorough re-evaluation of the sensitivity and specificity of microscopy and these newer diagnostic methods, with an estimation of the cost-effectiveness of each technique, is recommended.

Diagnosis of schistosomiasis by reagent strip test for detection of circulating cathodic antigen

A newly developed reagent strip assay for the diagnosis of schistosomiasis based on parasite antigen detection in urine of infected individuals was evaluated. The test uses the principle of lateral flow through a nitrocellulose strip of the sample mixed with a colloidal carbon conjugate of a monoclonal antibody specific for Schistosoma circulating cathodic antigen (CCA). The strip assay to diagnose a group of highly infected schoolchildren in Mwanza, Tanzania, demonstrated a high sensitivity and association with the intensity of infection as measured both by egg counts, and by circulating anodic antigen and CCA levels determined by enzyme-linked immunosorbent assay. A specificity of ca. 90% was shown in a group of schistosome-negative schoolchildren from Tarime, Tanzania, an area where schistosomiasis is not endemic. The test is easy to perform and requires no technical equipment or special training. The stability of the strips and the conjugate in the dry format lasts for at least 3 months at ambient temperature in sealed packages, making it suitable for transport and use in areas where schistosomiasis is endemic. This assay can easily be developed to an end-user format.

Immunodiagnostically applicable monoclonal antibodies to the circulating anodic antigen of Schistosoma mansoni bind to small, defined oligosaccharide epitopes

Gut-associated glycoproteins constitute a major group of the circulating excretory antigens produced by human Schistosoma species. The O-glycans of the relatively abundant circulating anodic antigen (CAA) from S. mansoni carry long stretches of unique -->6(GlcA beta 1-->3)GalNAc beta 1--> repeats. Specific anti-carbohydrate monoclonal antibodies (mAbs) are essential tools for the immunodiagnostic detection of CAA in the serum or urine of Schistosoma-infected subjects. In order to define the epitopes recognised by these anti-CAA mAbs, we screened a series of protein-coupled synthetic di- to pentasaccharide building blocks of the CAA polysaccharide for immunoreactivity, using ELISA and surface plasmon resonance spectroscopy. It was shown that anti-CAA IgM mAbs preferentially recognise -->6(GlcA beta 1-->3)GalNAc beta 1--> disaccharide units. Interestingly, no mouse anti-CAA mAbs of the IgG class were found that bind to the synthetic epitopes, although many of the IgG mAbs tested do recognise native CAA in a carbohydrate-dependent manner. In addition, both IgM and IgG class antibodies could be detected in human infection sera using the synthetic CAA fragments. These synthetic schistosome glycan epitopes and their matching set of specific mAbs are useful tools that further the development of diagnostic methods and are helpful in defining the immunological responses of the mammalian hosts to schistosome glycoconjugates.

Cellular and humoral immune responses and protection against schistosomes induced by a radiation-attenuated vaccine in chimpanzees

The radiation-attenuated Schistosoma mansoni vaccine is highly effective in rodents and primates but has never been tested in humans, primarily for safety reasons. To strengthen its status as a paradigm for a human recombinant antigen vaccine, we have undertaken a small-scale vaccination and challenge experiment in chimpanzees (Pan troglodytes). Immunological, clinical, and parasitological parameters were measured in three animals after multiple vaccinations, together with three controls, during the acute and chronic stages of challenge infection up to chemotherapeutic cure. Vaccination induced a strong in vitro proliferative response and early gamma interferon production, but type 2 cytokines were dominant by the time of challenge. The controls showed little response to challenge infection before the acute stage of the disease, initiated by egg deposition. In contrast, the responses of vaccinated animals were muted throughout the challenge period. Vaccination also induced parasite-specific immunoglobulin M (IgM) and IgG, which reached high levels at the time of challenge, while in control animals levels did not rise markedly before egg deposition. The protective effects of vaccination were manifested as an amelioration of acute disease and overall morbidity, revealed by differences in gamma-glutamyl transferase level, leukocytosis, eosinophilia, and hematocrit. Moreover, vaccinated chimpanzees had a 46% lower level of circulating cathodic antigen and a 38% reduction in fecal egg output, compared to controls, during the chronic phase of infection.

Profiles of immunoglobulin M (IgM) and IgG antibodies against defined carbohydrate epitopes in sera of Schistosoma-infected individuals determined by surface plasmon resonance

We report here that sera of children and adults infected with Schistosoma mansoni, S. haematobium, or S. japonicum contain antibodies against GalNAcbeta1-4(Fucalpha1-2Fucalpha1-3)GlcNAc (LDN-DF) and to a lesser extent to Galbeta1-4(Fucalpha1-3)GlcNAc (Lewis(x)) and GalNAcbeta1-4GlcNAc (LDN). Surface plasmon resonance (SPR) spectroscopy was used to monitor the presence of serum antibodies to neoglycoconjugates containing these carbohydrate epitopes and to define the immunoglobulin M (IgM) and IgG subclass distribution of the antibodies. The serum levels of antibodies to LDN-DF are high related to LDN and Lewis(x) for all examined groups of Schistosoma-infected individuals. A higher antibody response to the LDN-DF epitope was found in sera of infected children than in sera of infected adults regardless of the schistosome species. With respect to the subclasses, we found surprisingly that individuals infected with S. japonicum have predominantly IgG antibodies, while individuals infected with S. mansoni mainly show an IgM response; high levels of both isotypes were measured in sera of individuals infected with S. haematobium. These data provide new insights in the human humoral immune response to schistosome-derived glycans.

The fibre-web blood sampling technique applied to serological diagnosis of schistosomiasis mansoni

The fibre-web technique for sampling, storing and transport of venous or capillary blood has been evaluated, in 84 schoolchildren from the Mwanza region of Tanzania, with regard to diagnostic efficacy for determination of the schistosome circulating anodic antigen (CAA) under conditions similar to those prevailing in the field. Although the average concentrations determined in fibre-web eluates were only about half of those determined in serum, the prevalences of CAA-positive individuals for the 2 sample materials were approximately the same. The average coefficient of variation calculated on determination of CAA in venous-blood fibre-web eluates amounted to 7%. The study shows that the fibre-web technique is well suited for use under field conditions.

Various stages of schistosoma express Lewis(x), LacdiNAc, GalNAcbeta1-4 (Fucalpha1-3)GlcNAc and GalNAcbeta1-4(Fucalpha1-2Fucalpha1-3)GlcNAc carbohydrate epitopes: detection with monoclonal antibodies that are characterized by enzymatically synthesized neoglycoproteins

We report here that fucosylated epitopes such as Lewis(x), LacdiNAc, fucosylated LacdiNAc (LDN-F) and GalNAcbeta1-4(Fucalpha1-2Fucalpha1-3)GlcNAc (LDN-DF) are expressed by schistosomes throughout their life cycle. These four epitopes were enzymatically synthesized and coupled to bovine serum albumin to yield neoglycoproteins. Subsequently these neoglycoproteins were used to probe a panel of 188 monoclonal antibodies obtained from infected or immunized mice, in ELISA and surface plasmon resonance analysis. Of these antibodies, 25 recognized one of the fucosylated structures synthesized, indicating that these structures are immunogenic during infection. The MAbs identified could be subdivided in four different groups based on the recognition of either the Lewis(x)-, the LacdiNAc-, the LDN-DF-, or both the LDN-F- and LDN-DF epitope. These monoclonal antibodies were then used to investigate the localization of the fucosylated epitopes in various stages of Schistosoma mansoni using indirect immunofluorescence. Lewis(x)epitopes were mainly found in the gut and on the tegument of adult worms, on egg shells, and on the oral sucker of cercariae. The LacdiNAc epitope was expressed on the tegument of adult worms, on miracidia, and on the oral sucker of cercariae. In contrast, LDN-DF epitopes were mainly present in the excretory system of adult worms, on miracidia and on whole cercariae. These also stained positive with the LDN-F/LDN-DF epitope antibodies, while whole parenchyma reacted characteristically only with the latter antibodies. The identification of different carbohydrate structures in various stages of schistosomes may lead to a better understanding of the function of glycans in the immune response during infection.

Epidemiology of HIV and Schistosoma mansoni infections among sugar-estate residents in Ethiopia

Few studies have examined the interaction between schistosomiasis and infection with human immunodeficiency virus (HIV). The overlap between the two infections, and the effect of HIV infection on the egg output and worm load of individuals co-infected with Schistosoma mansoni, were therefore investigated in a sugar estate in central Ethiopia. The 1239 subjects were selected by stratified sampling of residents aged 15-54 years. The intensities of infection with S. mansoni were measured as egg output in stools (all subjects) and as the concentration of circulating cathodic antigen (CCA) in urine (a proxy for worm load, measured in 287 subjects). Schistosome infection was detected in 358 subjects [adjusted prevalence (AP) = 31.4%] and HIV infection in 52 (AP = 3.1%). The two infections clustered into different populations of the estate: the schistosome infections were predominantly found in the camps, and primarily affected young people (aged < 20 years) and those working in the field, whereas the HIV epidemic was found in the main village, primarily affecting those aged > 20 years and those who had recently arrived on the estate. Schistosome infection was detected in 348 of the 1187 HIV-negatives (AP = 31.6%) and 10 of the 52 HIV-positives (AP = 25.1%; P > 0.05). Schistosoma mansoni egg output was significantly lower in the HIV-positives than in the HIV-negatives (Mann-Whitney test; P = 0.03; ratio of geometric means = 0.74), and remained so after controlling for potential confounders (gender, age, and residence). However, CCA concentrations (i.e. worm loads) were found to be similar for these two groups, after controlling for potential confounders (age, gender, residence, and duration of residence).

The contribution of host-related factors to low cure rates of praziquantel for the treatment of Schistosoma mansoni in Senegal

Surprisingly low cure rates were repeatedly observed after treatment with a standard dosage of praziquantel in a recently established Schistosoma mansoni focus in northern Senegal. In 4 discrete cohorts from the same population, cure rates were 18-36% and egg count reduction rates were 77-88%. Data and material of 920 compliant subjects from all 4 cohorts were further analyzed to identify possible host-related factors associated with low cure rates. The lowest cure rates were found in the highest egg count groups. However, in low and moderate egg count groups, drug efficacy was also below normal values. Cure rates were similar in males and females, showed no seasonal variation, and were independent of previous praziquantel treatment. They were significantly higher in adults than in children, also after allowing for intensity of infection. Individual water contact behavior and specific humoral immune responses were examined in 2 extreme subgroups, either without significant egg count reduction or showing complete parasitologic cure. There was no significant difference in frequency and duration of water contact between those individuals with complete cure and those that showed little effect of praziquantel treatment. Levels of IgG, IgG1, IgG3, IgG4, IgM, and IgE against adult worm antigen were not different between the 2 subgroups. Thus, the abnormally frequent failure of treatment observed in this focus could not be associated with any host-related factor, other than age and pretreatment egg counts.

Development of antibody isotype responses to Schistosoma mansoni in an immunologically naive immigrant population: influence of infection duration, infection intensity, and host age

We have identified the influence of host and parasite factors that give rise to characteristic antibody isotype profiles with age seen in human populations living in different areas of schistosomiasis endemicity. This is important in the immunobiology of this disease. It is also of interest in the context of human responses to chronic antigen stimulation, vaccines, allergens, and other pathogens. In populations exposed to endemic schistosomiasis, factors such as intensity and duration of infection are age dependent. They therefore confound the influence of host age on antiparasite responses. Here, we resolved these confounding factors by comparing the developing antibody responses of an immunologically naive immigrant population as they acquired the infection for the first time with those of chronically infected resident inhabitants of the same region of Schistosoma mansoni endemicity in Kenya. Recent arrival in the area strongly favored immunoglobulin G3 (IgG3) responses against the parasite. The antibody isotype responses associated with human susceptibility to reinfection after chemotherapy were elevated in those suffering high intensities of infection (IgG4 responses against worm and egg antigens) or were characteristic responses of young children irrespective of the intensity or duration of infection (IgG2 responses against egg antigen). IgE responses against the adult worm, a response associated with resistance to reinfection after chemotherapy, increased with the ages of infected individuals and were also favored in those currently suffering higher intensities of infection.

The dynamics of a soluble egg antigen of Schistosoma haematobium in relation to egg counts, circulating anodic and cathodic antigens and pathology markers before and after chemotherapy

A cohort of Schistosoma haematobium infected schoolchildren from Cameroon (n = 146) was studied for urine circulating soluble egg antigen (SEA), in comparison to other urine infection parameters: the circulating adult worm-derived antigens, circulating anodic and cathodic antigens (CAA and CCA), egg counts and the reagent strip index (RSI). Before treatment, SEA prevalence was 90%, while 89% and 65% of the children were positive for CCA and CAA respectively. The children were treated with 2 doses of praziquantel (2 x 40 mg/kg bodyweight) at an interval of 10 days and followed-up at 1, 2, 3, 5 and 12 months after treatment. Urine SEA correlated significantly with egg counts and RSI; levels of CAA and CCA were also significantly correlated with those of SEA. The levels of SEA showed a better correlation to both egg counts and RSI than did the levels of CAA and CCA. SEA levels dropped sharply 1 month after treatment, with few children excreting any SEA whereas egg counts decreased less rapidly. The prevalence and levels of SEA remained low during the whole post-treatment period whereas egg counts, RSI and CCA in urine rose progressively in the post-treatment period with a final egg count prevalence of 78%. The results of the present study indicate that for S. haematobium infections, measurement of SEA in urine is a valuable additional diagnostic parameter.

Human IgE, IgG subclass, and IgM responses to worm and egg antigens in schistosomiasis haematobium: a 12-month study of reinfection in Cameroonian children

Levels of IgE, IgM, and IgG subclasses against Schistosoma haematobium adult worm antigen (AWA) and soluble egg antigen (SEA) in a cohort of 148 S. haematobium-infected schoolchildren were determined before and up to 12 months after chemotherapy. Infection intensities were determined as concentrations of circulating anodic antigen (CAA) in serum. One month posttreatment, the antibody levels of all isotypes against AWA were increased, but 1 year after treatment they returned to pretreatment levels. CAA concentrations were positively associated with levels of IgG4 against AWA and SEA but not with levels of IgE. Age correlated negatively with CAA concentrations and positively with levels of IgE to AWA. The balance of anti-AWA IgG4 and IgE was significantly correlated to the CAA concentration, in particular in the older age group (11-13 years). This may suggest that protective immune mechanisms in S. haematobium infections become effective around the age of 12 years.

Anti-schistosome IgG4 and IgE at 2 years after chemotherapy: infected versus uninfected individuals

Specific IgG4 and IgE responses to adult worm antigen (AWA) and soluble egg antigen (SEA) were examined in 37 subjects from an area in which schistosomiasis is endemic, who were previously infected with Schistosoma haematobium and who became reinfected or remained free of infection 2 years after chemotherapy. The reinfected group was significantly younger (median age, 11 years) than the uninfected group (median age, 24 years). Posttreatment levels of IgG4 to egg antigens (IgG4-SEA) were significantly correlated with reinfection intensity (r = .74, P < .0001), and 13-fold lower levels of IgG4-SEA were observed in uninfected subjects compared with reinfected subjects. Although no correlation was observed between posttreatment IgE to AWA or to SEA, pretreatment IgE-AWA was inversely correlated with the level of reinfection (r = -.39, P = .02).

Schistosoma mansoni excretory circulating cathodic antigen shares Lewis-x epitopes with a human granulocyte surface antigen and evokes host antibodies mediating complement-dependent lysis of granulocytes

Parasitic worms of the genus Schistosoma excrete relatively large amounts of immunogenic glycoproteins (circulating cathodic antigen [CCA]) that contain polysaccharide side chains with the trisaccharide Lewis-x (L(ex)) as a repeating unit. These carbohydrates evoke high titers of specific IgM antibodies that cross-react with the repeating L(ex) units on the surface of granulocytes. Consequently this might lead, in the presence of complement, to lysis of the granulocytes. In the present study, this hypothesis was investigated using anti-CCA mouse monoclonal antibodies (MoAbs) and polyclonal antibodies purified from sera of infected humans. By flow cytometry, it was demonstrated that the mouse MoAbs directed against CCA strongly recognized the granulocytes. It could also be shown that these MoAbs, as well as anti-CCA IgM antibodies purified from infected human sera, caused lysis of granulocytes in a complement-dependent cytotoxicity assay. Sera from healthy controls or from patients with other helminth infections resulted in negligible granulocytotoxicity. These in vitro observed phenomena may explain the mild to moderate neutropenia that occurs in schistosomiasis patients.

Schistosoma mansoni: in vitro and in vivo excretion of CAA and CCA by developing schistosomula and adult worms

In this study we describe the excretion patterns of circulating anodic (CAA) and cathodic antigen (CCA) by freshly transformed and developing Schistosoma mansoni schistosomula and adult worms. In vitro, CAA and CCA were excreted by the parasites immediately after transformation. During the first days of development CAA and CCA levels were similar, but after 1 wk more CCA was excreted. Neither feeding the schistosomula with red blood cells nor addition of colchicine influenced the rates of antigen excretion. Female worms produced more antigen than males. In heavily infected mice CCA was the first antigen detectable from the third week of infection onward. A few days later, CAA showed a steep increase, becoming the predominant antigen during the course of infection. In urine samples, obtained at the time of perfusion (7 wk), CCA was the predominant antigen. In conclusion, although CAA and CCA levels in serum and urine generally correlate well with worm burden (as determined by egg output), the present study and a literature review show that the actual quantities produced by the worms and detected in the host circulation or excreta may depend on many factors, e.g., host and parasite species, clearance rates, or duration and intensity of infection.

Antischistosome IgG4 and IgE responses are affected differentially by chemotherapy in children versus adults

Specific IgG4 and IgE responses and polyclonal cytokine profiles were studied in 110 Schistosoma haematobium-infected persons before and 5 weeks after chemotherapy. Pretreatment IgG4 responses to soluble egg antigen (SEA) correlated with intensity of infection. After chemotherapy, a significant decrease in egg output and circulating anodic antigen was associated with a substantial drop in the IgG4 response to SEA (IgG4-SEA) in adults and children, suggesting that egg laying is a major stimulus for IgG4-SEA. After chemotherapy, IgG4 and IgE to adult worm antigen and IgE to SEA increased in children but remained unchanged in adults. This indicates that the immunoregulatory mechanisms operative in S. haematobium-infected adults differ from those in infected children. The effect of treatment on cytokine profiles was determined following stimulation of whole blood with anti-CD3 antibodies. A significant decrease in interleukin-4 production after treatment indicated that reduction in helminth load may lead to a reduced number of Th2-type cells.

Antibody response patterns against Schistosoma mansoni in a recently exposed community in Senegal

Acquired immune resistance is believed to be largely responsible for age-dependent infection and reinfection patterns in schistosomiasis. In a recently established but intense focus of Schistosoma mansoni in Senegal, the humoral immune response was studied in a random population sample of 289. Antibody levels of various isotypes to schistosome worm and egg antigens were determined by ELISA and related to egg counts (eggs per gram of feces [EPG]), age, and sex. Both IgG1 and IgG4 followed age-related patterns similar to egg counts and strongly correlated with EPG, even after allowing for age. Specific IgE levels increased slowly with age. The humoral immune response patterns in this recently infected population appeared to be largely similar to those in chronically infected communities. Thus far, the observations do not support the current hypothesis that age-related resistance to Schistosoma is determined by IgE-mediated protective immunity acquired during many years of exposure.

Schistosoma: analysis of monoclonal antibodies reactive with the circulating antigens CAA and CCA

Using spleen cells of mice infected or immunized respectively with cercariae or antigen preparations of Schistosoma mansoni, S. haematobium or S. japonicum monoclonal antibodies (mAbs) were produced against the schistosome gut-associated antigens CAA (circulating anodic antigen) and CCA (circulating cathodic antigen). Fusions nearly exclusively produced either anti-CAA (n = 25) or anti-CCA mAbs (n = 55) with a strong isotype restriction (IgM, IgG1 and IgG3) against both antigens, the majority of anti-CAA mAbs being IgG1 and the majority of anti-CCA mAbs being IgM. The mAbs, which on the basis of their selection were reactive with multiple carbohydrate epitopes of CAA or CCA, were applied in different immunological techniques including immunofluorescence, a dot immunobinding assay and immunoelectrophoresis to study the epitope repertoire. Anti-CAA mAbs were found to be reactive with 5 different epitopes, none of which occurred as multiple epitopes on eggs. Anti-CCA mAbs, on the other hand, recognized at least 10 different epitopes, while 44% of anti-CCA mAbs recognized epitopes common to the adult worm and the egg. Both CAA- and CCA-epitopes were found to be developmentally expressed at the level of the tegument in cercariae, schistosomula and 5-day-old lung worms, but in the adult worm were primarily found in the gut. Thus, the production of panels of mAbs has not only resulted in the selection of reagents optimally performing in diagnostic immunoassays, but also allowed a more detailed study of the epitope repertoire of these important schistosome antigens.

The immunologically reactive part of immunopurified circulating anodic antigen from Schistosoma mansoni is a threonine-linked polysaccharide consisting of --> 6)-(beta-D-GlcpA-(1 --> 3))-beta-D-GalpNAc-(1 --> repeating units

The gut-associated excretory antigen CAA (circulating anodic antigen) from adult Schistosoma mansoni worms was isolated by immunoaffinity chromatography. Amino acid analysis following alkaline borohydride treatment indicated that CAA is a glycoprotein, O-glycosylated at Thr. The primary structure of the released O-glycan moiety was investigated by one- and two-dimensional, homo- and heteronuclear 1H and 13C NMR spectroscopy. It was found that the major carbohydrate chains have a novel polysaccharide structure, consisting of a branched disaccharide repeating unit containing 2-acetamido-2-deoxy-beta-D- galactopyranose (beta-D-Galp-NAc) and beta-D-glucopyranuronic acid (beta-D-GlcpA). [formula: see text] The major antigenic character of CAA arises from this novel polysaccharide, which was shown to be an absolutely specific diagnostic marker in schistosomiasis. The cross-reactivity of CAA with anti-CCA (circulating cathodic antigen) monoclonal antibodies is caused by the presence of a small amount of O-linked CCA-poly-Lewis x carbohydrate chains on the CAA protein chain.

Schistosoma mansoni circulating anodic antigen but not circulating cathodic antigen interacts with complement component C1q

Adult schistosome parasites, living in the blood vessels of their mammalian hosts, protect themselves against immune damage in a variety of ways. In addition to the tegument, the intestinal epithelium of the blood-feeding worms is permanently exposed to both the innate and the acquired immune system. In this study, we investigated whether the Schistosoma gut-associated antigens CAA and CCA (circulating anodic antigen and circulating cathodic antigen, respectively), which are excreted in relatively large quantities into the host's circulation, might play a role in evading complement attack. Of several complement components tested, only purified C1q showed significant binding to CAA, a negatively charged highly glycosylated glycoprotein. CCA, also highly glycosylated, but neutral or slightly positively charged, did not bind to C1q. CAA bound only to the collagen-like stalks of C1q and not to the globular heads. No detectable interaction of CAA with precursor human C1 was found and CAA did not induce activation of C1 in whole human serum as assessed by consumption of hemolytic C4 activity. Also CAA could not induce activation of precursor C1 in vitro. These results suggest that CAA behaves like a receptor for C1q, and might be involved in protecting the vulnerable schistosome gut against complement-mediated attack.

Schistosoma mansoni: analysis of monoclonal antibodies reactive with gut-associated antigens

The analysis of a series of monoclonal antibodies (mAbs) developed in our laboratory against gut-associated antigens of Schistosoma mansoni is described. It was found that mAbs that recognized epitopes of antigens in the gut and on the eggshell were mainly of the IgM isotype; these epitopes are likely to be carbohydrate in composition. Of a number of mAbs that were reactive with antigens important to the human humoral immune response, 75% appeared to be reactive with the circulating cathodic antigen.

Application of the FITC-anti-FITC-gold system to ultrastructural localization of antigens

We report the application of a fluorescein isothiocyanate (FITC)-anti-FITC method to localize antigens at the ultrastructural level. In the systems studied, the anti-FITC-based detection method displays high specificity and sensitivity. These observations, combined with ease of production and with availability of FITC-protein conjugates, suggest that the FITC-anti-FITC method is a good alternative to presently used methods and is widely applicable to immunochemical and immunocytochemical procedures. The same preparation and protocol can be used for light and electron microscopic studies, thereby reducing possible artifacts introduced if different procedures are used. In the present study, two systems were used to test the method. One system used an FITC-labeled monoclonal antibody (MAb) to schistosome circulating cathodic antigen. In this system, the label was detected in the gut of adult Schistosoma mansoni by an anti-FITC MAb conjugated to 10-nm gold particles. The second system used human IgM antibodies pooled from patients infected with Schistosoma mansoni. In this system detection was accomplished using an anti-human IgM-FITC conjugate followed by the anti-FITC-Au antibody conjugate.

Detection of the schistosome circulating cathodic antigen by enzyme immunoassay using biotinylated monoclonal antibodies

We have developed an enzyme immunoassay (ELISA) for the quantification of the schistosome circulating cathodic antigen (CCA), a glycoprotein associated with the syncitium lining the gut of the parasite. A mouse monoclonal antibody of IgG3 isotype was used as coating (antigen-capture) antibody, while a biotinylated mouse monoclonal IgM was used as second (antigen-detecting) antibody. Streptavidin-alkaline phosphatase was used as enzyme label. The lower detection limit of the assay was 1.0 ng of the trichloroacetic acid soluble fraction of adult worm antigen (AWA-TCA) per ml, which corresponds to approximately 0.2 ng CCA per ml. The ELISA showed a linear range from 1.0 to 62.5 ng AWA-TCA per ml. Serum and urine samples of 16 individuals infected with Schistosoma mansoni (egg counts ranging from 5 to 4820 eggs per gram of faeces) were tested in the assay. Antigen titres ranged from less than 4-8192. This assay represents a considerable advantage in diagnosis of Schistosoma infections as it allows the detection and quantification of CCA in serum and urine in even lightly infected individuals.

Estimation of the avidity of antibodies in polyclonal antisera against Streptococcus pneumoniae type 3 by inhibition ELISA

The reliability of the determination of antibody avidity in polyclonal sera by indirect sandwich ELISA was studied. Binding of IgM and IgG (sub)classes in unpurified serum to Streptococcus pneumoniae type 3 capsular polysaccharide, which was coated onto ELISA plates, was inhibited with different inhibitors. The inhibitor concn at which 50% inhibition of antibody binding to the ELISA coat was achieved, was used as a measure for antibody avidity. As this 50% inhibition value is dependent upon the dilution of the serum and thus upon the initial amount of free antibody, it is necessary to define (a narrow range of) final ELISA absorbance values to which the dilutions of non-inhibited sera have to be adjusted. The shapes of the serum dilution curves have a good correlation with the numerical 50% inhibition values of the antibody avidity. The inhibition ELISA is suitable to compare the avidity values of the different antibody isotypes, but two remarks should be made: (1) antibody heterogeneity should be considered to influence the results and prevent the accurate measurement of absolute numerical avidity values. Because in the ELISA system merely antibody "activity" is measured, comparison of the efficacy of vaccines by means of the 50% inhibition (avidity) value of various antibody (sub)classes can still be performed in a reliable way; (2) results of the determination of the 50% inhibition values of the different antibody (sub)classes showed them to be dependent on the molecular ratio between antibody (sub)class levels. More aspects of the determination should be taken into account, like shapes of simple dilution curves, influences of various inhibitor concns in the diluent and whole (extended) inhibition curves.