Antibody response to a purified parasite proteinase (SMw32) in Schistosoma mansoni infected mice

Schistosoma mekongi cathepsin B and its use in the development of an immunodiagnosis

Schistosomiasis mekongi is one of the most important human parasitic diseases caused by Schistosoma mekongi in South-east Asia. The endemic area is the Mekong River sub-region from Laos to Cambodia. This parasite also infects dogs and pigs which are its alternative host species. Currently, the lack of reliable rapid diagnosis makes it difficult to monitor the infection and spreading of the disease. In this study, we screened the antigens of the parasite with sera of infected mice using Western blotting and identified proteins of interest with LC-MS/MS to obtain potential candidate proteins for diagnostic development. This assay yielded 2 immunoreactive bands at molecular masses of 31 and 22kDa. The 31kDa protein was the major band identified as cathepsin B, and its gene was cloned to obtain a full cDNA sequence (SmekCatB). The cDNA consisted of 1123bp and its longest reading frame encoded for 342 amino acids with some putative post translation modifications. The recombinant SmekCatB (rSmekCatB) with hexahistidine tag at the C-terminus was expressed in Escherichia coli and purified by Ni-NTA resin under denaturing conditions. The rSmekCatB reacted with sera of S. mekongi-infected mice. Indirect ELISA using rSmekCatB as the antigen to detect mouse antibodies, revealed a sensitivity of 91.67% for schistosomiasis mekongi and the specificity of 100%. Our data suggested that SmekCatB is one of the most promising parasitic antigens that could be used for the diagnosis of S. mekongi infection.

Rapid induction of IgE responses to a worm cysteine protease during murine pre-patent schistosome infection

BACKGROUND

During the pre-patent stage of infection, juvenile Schistosoma blood flukes co-opt signals from the adaptive immune system to facilitate parasite development, but the types of responses that are induced at this early stage of infection, and the parasite antigens they target, have not been characterized.

RESULTS

Through analysis of experimental pre-patent infections, we show that the S. mansoni cysteine protease SmCB1 is rapidly targeted by an antigen-specific IgE response. The induction of this response is independent of schistosome eggs as infection with male or female worms alone also induced SmCB1-specific IgE. We also show that the SmCB1-specific IgE response is dependent on cognate CD4+ T cell help and IL-4, suggesting that pre-patent Th2 responses provide T cell help for the SmCB1-specific IgE response. Finally, exposed human subjects also produced IgE against SmCB1.

CONCLUSIONS

Our data demonstrate that, like eggs, schistosome worms also induce functional type 2 responses and that a parasite cysteine protease is an inducer of type 2 responses during the early stages of schistosome infection.

Preliminary characterization of an adult worm “vomit” preparation of Schistosoma mansoni and its potential use as antigen for diagnosis

Schistosoma mansoni is a parasitic trematode of the portal-mesenteric veins with a closed-end intestine. Adult worms regurgitate their intestinal content after digestion, together with constituents of the lining gut. Some of these molecules circulate in the blood and are antigenic. We obtain a "vomit" preparation and preliminary evaluate its biochemical composition and antigenic capacity. The "vomit" preparation was obtained after changes in temperature and solutions of incubation of adult worms between 4 and 37 degrees C. Supernatant was assayed for protein, carbohydrate concentration and enzymatic activities associated to the intestine and to the worm tegument. The antigenicity of the product was evaluated using Western blot (WB) analysis against sera of experimentally infected mice, before and after drug cure, sera from people infected with S. mansoni and from individuals infected with other parasitoses. More carbohydrate than protein was detected in the preparations. Cysteine proteinase (CP), N-acetyl-beta-D: -glucosaminidase and alkaline phosphatase activities were detected. The latter enzyme activity is a marker of the tegument, suggesting that in spite of careful conditions used to avoid the presence of tegumental material, manipulation of the worms always resulted in the release of tegumental molecules. Cationic exchange chromatography was useful to separate various components of this "vomit" preparation, particularly enzymes responsible for CP activity. Two highly immunogenic and specific duplets were observed in the WB analysis, 31/32- and 38/40-kDa components, the former probably referring to the intestinal CPs Sm31/Sm32. None of the two duplets disappeared after successful chemotherapy during the time of evaluation in mice or humans.

Setaria cervi: in vitro released collagenases and their inhibition by Wuchereria bancrofti infected sera

In vitro released products of adult Setaria cervi females, microfilariae and extracts showed considerable amounts of collagenase activity. On the basis of per mg protein released in vitro, the products of both microfilariae and adult females exhibited comparable activity but this was much higher than that of extract of microfilariae and adult females. Two collagenase enzymes with molecular masses of 50 kDa and 70 kDa were separated using DEAE-sepharose CL6B and Sephadex G-100 column chromatography. The 50 kDa and 70 kDa collagenase exhibited pH optima of 5.2 and 7.0, respectively. Considering specific activity, the 50 kDa enzyme was found to contribute about ten times more collagenase activity as compared to the 70 kDa enzyme. An inhibition study revealed obvious differences between them. Thiol group inhibitors such as N-ethylmaleimide and leupeptin inhibited the 50 kDa enzyme but this was strongly activated by dithiothreitol, a thiol group stabilizer. Alternatively, the 70 kDa enzyme showed a sensitivity to a metal chelator and a serine group inhibitor indicating its metalloserine protease nature. The antifilarial drug diethylcarbamazine did not demonstrate any inhibition under in vitro conditions. Both enzymes were significantly inhibited by antibody IgG separated from Wuchereria bancrofti infected human sera, showing a possible immunoprotective role.

Cystatin capture enzyme-linked immunosorbent assay for serodiagnosis of human clonorchiasis and profile of captured antigenic protein of Clonorchis sinensis

Enzyme-linked immunosorbent assay (ELISA) with crude extracts of adult Clonorchis sinensis has been reported to have a high degree of sensitivity with a moderate degree of specificity for the serodiagnosis of clonorchiasis. The cystatin capture ELISA was investigated for its usefulness for the serodiagnosis of human clonorchiasis. Cystatin bound specifically to cysteine proteinases in crude extracts of adult C. sinensis worms, and its binding capacity was not hindered competitively by the other proteinase inhibitors tested. The cystatin capture ELISA for clonorchiasis showed a higher degree of specificity than the conventional ELISA, which produced some cross-reactivities to sera from patients with cysticercosis, sparganosis, and opisthorchiasis. Immunoglobulin G antibodies to C. sinensis cysteine proteinases were produced in experimental rabbits at week 3, and their levels increased rapidly and remained at a plateau after 8 weeks of infection. Of the proteins from the C. sinensis crude extract captured with cystatin, seven proteins were reactive with the serum from patients with clonorchiasis. The cystatin capture ELISA is indicated to be a sensitive and highly specific immunodiagnostic assay for serodiagnosis of human clonorchiasis.

The role of hepatitis C in hepatocellular carcinoma: a case control study among Egyptian patients

BACKGROUND

Egypt has one of the highest prevalence rates of hepatitis C virus (HCV) infection in the world; however, the risk and attribution related to HCV in Egyptian patients with hepatocellular carcinoma (HCC) remains unknown.

GOALS

The current study was undertaken to estimate the risk of HCC in relation to HCV in Egypt.

STUDY

Thirty-three patients with HCC and 35 healthy controls who had a similar socioeconomic status were prospectively enrolled at the University of Cairo National Cancer Institute.

RESULTS

Anti-HCV antibodies were present in 75.8% of the patients and in 42.9% of the controls (p = 0.01); hepatitis B surface antigen (HBsAg) was present in 15.2% of the patients and in 2.9% of the controls (p = 0.03). In addition, the sex-and age-adjusted odds ratio (OR) for anti-HCV antibodies was 5.1 (95% CI = 1.5-17.4) and for HBsAg was 13.2 (95% CI = 1.2-148.2). Concurrent Schistosoma mansoni and anti-HCV was associated with an OR of 10.3 (95% CI = 1.3-79.8), which was higher than that for anti-HCV (6.5; 95% CI = 1.6-26.6) and S. mansoni infection (0.2; 95% CI = 0.1-6.2) alone. Finally, we estimated the attributable fraction of HCC to HCV to be 64% in this study population and 48% in the general Egyptian population.

CONCLUSIONS

Both HCV and hepatitis B virus infection increase the risk of HCC in Egyptian patients, whereas isolated Schistosoma infection does not. Because of the very high prevalence rate of HCV in the general Egyptian population, it accounts for most HCC cases in Egypt.

Antibody responses to fluke cysteine proteinases in Paragonimus- and Fasciola-infected rats

IgG and IgM antibody responses to fluke cysteine proteinases in Paragonimus ohirai- and Fasciola sp.-infected rats were followed by means of cystatin capture ELISA using fluke excretory-secretory products for 10 weeks after infection. The specific IgG antibodies were detectable at week 2 postinfection in all P. ohirai-infected and some Fasciola-infected rats. Levels of specific IgG antibodies increased rapidly between week 2 and 6, and slightly thereafter, in both infected groups. From week 3, specific IgG antibody levels were higher in Fasciola-infected than P. ohirai-infected rats. Sera from infected rats did not react with heterologous cysteine proteinases throughout the infection periods. In both infected groups, the kinetic patterns of specific IgM antibody responses were similar to those of specific IgG antibody responses although the ELISA levels of the IgM antibody responses were much lower. In abnormal infections with P. ohirai metacercariae x-irradiated at 2 krad, the specific IgG antibodies were detectable at week 2 postinfection with similar ELISA values to normal P. ohirai infection, but thereafter increased little. In infections with P. westermani, for which the rat is not a suitable host, even stunted worms induced a comparable specific IgG antibody response, although the response was lower than in normal infections with P. ohirai. These results indicate that cystatin capture ELISA can distinguish clearly between Paragonimus and Fasciola infections which show immunodiagnostic cross-reactivity and is useful even in the early stages of the infection and in the infection of unsuitable hosts.

Immunodiagnosis of fasciolosis in ruminants using a 28-kDa cysteine protease of Fasciola gigantica adult worms

A homogeneous extract of a 28-kDa cysteine protease of Fasciola gigantica adult worms was used as the antigen for immunodiagnosis of fasciolosis in cattle, sheep and goats using the Falcon assay screening test enzyme-linked immunosorbent assay technique. This antiprotease assay technique was found to be very rapid and sensitive and may be useful as a supplementary method for the diagnosis of fasciolosis in ruminants.

Development and characterization of a monoclonal antibody reactive with a 28 kDa protease of Fasciola gigantica

A monoclonal antibody that was reactive with a 28-kDa protease of Fasciola gigantica was produced after hyperimmunizing BALB/c mice with a partially purified extract and a purified 28-kDa protease obtained from the fluke. Isotype analysis showed that the immunoglobulin is IgG3. Seven other monoclonals of isotypes IgG1, IgG2 and IgG3 which reacted with the protease and one to three other protein bands were also produced. In addition, four other clones of hybridoma produced antibodies which recognised a 27/28-kDa protein doublet but the 28-kDa component of this doublet was different from the 28-kDa protease. The reactivities and characteristics of the monoclonal antibodies were studied by enzyme-linked immunosorbent assay (ELISA), immunoblotting and immunoprecipitation tests.

The immunologically reactive O-linked polysaccharide chains derived from circulating cathodic antigen isolated from the human blood fluke Schistosoma mansoni have Lewis x as repeating unit

The gut-associated excretory antigen circulating cathodic antigen (CCA) was isolated by immunoaffinity chromatography from adult Schistosoma mansoni worms, which were collected from infected golden hamsters. This antigen is probably involved in protection of the schistosome gut and is increasingly used in highly sensitive and specific immunodiagnostic assays. Amino acid analysis before and after alkaline borohydride treatment of CCA and monosaccharide analysis indicated that CCA is O-glycosylated mostly via GalNAc-Thr. After reductive alkaline treatment, the O-linked carbohydrate chains were fractionated by gel-permeation chromatography, followed by normal-phase HPLC on LiChrosorb-NH2. Carbohydrate-positive fractions were investigated by one-dimensional and two-dimensional 1H-NMR spectroscopy, fast atom bombardment mass spectrometry and collision-induced-dissociation tandem mass spectrometry. The analyses showed that the low-molecular-mass O-linked oligosaccharide alditols (the minor fraction) consist of disaccharides to hexasaccharides having the Gal beta (1-3)GalNAc-OL core in common. The major carbohydrate fraction comprises a population of polysaccharides, containing Lewis x repeating units (-3)Gal beta (1-4)[Fuc alpha (1-3)]GlcNAc beta (1-). CCA-specific monoclonal antibodies and IgM antibodies in patient sera recognized the fucosylated O-linked carbohydrate antigenic structures. Since CCA evokes a strong IgM antibody response and carbohydrate structures containing repeating Lewis x units are found on circulating neutrophils, it is proposed that the antigenic poly-Lewis x polysaccharide of CCA is involved in the induction of auto-immunity against granulocytes, resulting in the mild to moderate neutropenia observed during schistosome infection.

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.

Candidate vaccine antigens identified by antibodies from mice vaccinated with 15- or 50-kilorad-irradiated cercariae of Schistosoma mansoni

In murine schistosomiasis, the highest levels of resistance to cercarial challenge are obtained by vaccination with radiation-attenuated cercariae. To identify candidate vaccine antigens relevant to the vaccine model, we examined parasite antigens recognized by antibodies from mice vaccinated with irradiated cercariae of Schistosoma mansoni. To optimize recognition of a wide spectrum of antigens, several factors that influence the level of protection in this model were varied; specifically, we examined the effect of (i) single versus multiple vaccinations with irradiated cercariae, (ii) the dose of irradiation (15 or 50 kilorads) administered to the cercariae, and (iii) the genetic background of mouse strains, high-responder (C57BL/6J) versus moderate-responder (CBA/J) mice. We found that the number of vaccinations did not alter antibody specificity but modified the relative antibody titers against particular antigens. The dose of irradiation used to attenuate the immunizing cercariae had a similar effect on antibody titers but in addition influenced antibody specificity. Only mice that had been vaccinated with moderately irradiated cercariae recognized cathepsin B (Sm31) and Sm32. Interestingly, when vaccinated mice of the two strains, C57BL/6J and CBA/J, were compared, differences in antibody responses to particular antigens were observed. Both strains recognized the integral membrane protein Sm23, glutathione S-transferase, and cathepsin B, whereas Sm32 and paramyosin were recognized only by CBA/J mice, and heat shock protein 70 was recognized exclusively by C57BL/6J mice. In this study, we conclusively identified six distinct antigens that are specifically recognized by the humoral immune response of vaccinated mice.

Isolation and partial characterization of cysteine proteinase from sparganum

A proteolytic enzyme was purified from the tissue extract of spargana (plerocercoids of Spirometra erinacei) by DEAE-Trisacryl M ion exchange chromatography and thiopropyl-sepharose affinity chromatography resulted in a 21-fold purification. The proteinase activity was assayed with a synthetic fluorescent substrate, carbobenzoxy-phenylalanyl-7-amino-4-trifluoromethyl-coumarin. SDS-polyacrylamide gel electrophoresis of the purified materials revealed a single 28,000 dalton band. Inhibitor profiles of the band indicated that it belonged to cysteine endopeptidases. It exhibited identical pH curves with optimum at pH 5.5, and 50% activity from pH 4.7 to 8. It could completely degrade collagen chains to three identical products. It also showed some activity on hemoglobin. Furthermore, the band on immunoblots was reactive to the sera of sparganosis patients. These results suggest that the proteolytic enzyme belongs to cysteine proteinase which plays a role in the tissue penetration. Also it may be used as the antigen for diagnosis of active sparganosis.

The purification and characterization of a cysteine protease of Fasciola gigantica adult worms

A 26-28 kDa protease was isolated from Fasciola gigantica adult worms by a two-stage purification process of column chromatography in a Sephacryl S-200 column and affinity chromatography in an L-phenylalanine-agarose column. This protease is a cysteine (thiol) proteinase with an optimum pH of 4.5 and is not inhibited by anti F. gigantica immunoglobulin G. The enzyme was inhibited by protease inhibitors known to inhibit cysteine proteases but not by metallo-, aspartate or serine protease inhibitors. The effect of several protease inhibitors and anti-F, gigantica IgG was also assessed on the total proteolytic activity of F. gigantica. There appears to be a preponderance of cysteine protease activity in F. gigantica and there was a significant inhibition of total proteolytic activity by anti-F. gigantica IgG.

Partial purification and characterisation of the proteolytic enzymes of Fasciola gigantica adult worms

The proteases of adult Fasciola gigantica whole worm were analysed by preparative isoelectric focusing and by gelatin-substrate gel electrophoresis at acidic and neutral pH (4.5 and 7.0). At least 15 bands of proteases were observed. These proteases had molecular weights ranging from 26 to 193 kDa and isoelectric points of 4.92-7.63. Protease-rich fractions were subsequently separated from whole worm preparation of the parasite by filtration in Sephacryl S-200. The proteases were able to digest bovine immunoglobulin G (IgG) and globin (derived from bovine haemoglobin) in vitro. The sizes of the proteases in these fractions were from 26 to 96 kDa, and they were inhibited by the protease inhibitors phenylmethylsulphonyl fluoride (PMSF), leupeptin and trasylol.

Antigenicity of adult Schistosoma mansoni alkaline phosphatase

Antibodies to the alkaline phosphatase (AP) of Schistosoma mansoni in infected human and mice sera were evaluated by a direct solid-phase AP immunoadsorption assay (APIA) and by Western blot and immunostaining. APIA consisted of (a) solid-phase capture of immunoglobulins from infected human or mice, (b) immunoadsorption of the enzyme antigen by the antibodies, and (c) detection of the enzymatic activity. By this procedure the appearance of the anti-AP response in mice was detected around 50 days post-infection; this response was not specific for an AP of a given schistosome strain and it was not induced by an autoimmunity phenomenon. Fourteen out of 15 sera from infected people tested by APIA showed a clear antibody response against this enzyme. Immunoblots in non-reducing conditions supported APIA results indicating that the parasite AP was specifically recognized by the antibodies present in infected human and mice sera. These results suggest the possible usefulness of the schistosome AP as a marker for S. mansoni infection.

Cloned Schistosoma mansoni proteinase (hemoglobinase) as a putative serodiagnostic reagent

Expressed cDNA encoding a proteolytic enzyme from Schistosoma mansoni has been cloned recently. Circulating antibodies reacting with the recombinant protein have been detected in the blood of mice and humans infected with S. mansoni, S. japonicum, or S. haematobium. S. mansoni and S. haematobium infection can be distinguished by antibody titer.