Immunoblot patterns of clonorchiasis

Novel mechanism of hepatobiliary system damage and immunoglobulin G4 elevation caused by Clonorchis sinensis infection

Clonorchis sinensis infection is still a major public health problem. It is estimated that more than 15 million people worldwide are infected, especially in Northeast China, Taiwan, South Korea, and North Vietnam. The detection of Clonorchis sinensis eggs in feces and bile is still the only gold standard for the diagnosis of Clonorchis sinensis infection, and new detection methods are needed to improve the detection rate. After Clonorchis sinensis invades the human body, it mainly parasitizes the hepatobiliary tract. Therefore, it is closely related to hepatobiliary diseases such as cholangitis, bile duct stones, liver fibrosis, and cholangiocarcinoma. The increase in immunoglobulin G4 (IgG4) caused by Clonorchis sinensis infection is rare and there are few reports about the relevant mechanism. It may be related to the inflammatory factors interleukin (IL)-4, IL-10, and IL-13 produced by human phagocytes, T cells, B cells, and other immune cells in the process of resisting the invasion of Clonorchis sinensis. However, this finding still needs further clarification and confirmation. This article reviews the epidemiology, clinical manifestations, serology, imaging, pathogenic mechanism, and control measures of Clonorchis sinensis infection to help establish the diagnostic process for Clonorchis sinensis. We report novel mechanisms of IgG4 elevation due to Clonorchis sinensis infection to provide more experience and a theoretical basis for clinical diagnosis and treatment of this infection.

Relationships Between IgG, IgM, IgE and Resistance to Reinfection During the Early Phase of Infection withClonorchis sinensisin Rats

An enzyme linked immunosorbent assay (ELISA) was used to study the correlation between the levels of IgG, IgM and IgE immunoglobulin isotypes and resistance to reinfection in rats during the first month of infection with Clonorchis sinensis. Rats were infected with Clonorchis sinensis (primary infection), and then treated with praziquantel on the 1st, 3rd, 7th, 14th and 28th day post infection (p.i.). To measure resistance, rats were re-infected with C. sinensis (secondary infection), 2 weeks after the treatment and worms were recovered 4 weeks later. During the primary infection, significantly increased levels of IgG isotype were observed on days 14 and 28 p.i. (P < 0.001) and IgM levels were significantly increased on 3rd and 28th day (P < 0.001). During the secondary infection, significantly increased levels of IgG isotype were found from 3rd to 28th day and IgE isotype on 7th and 14th day (P < 0.01) while significant levels of IgM were found on the 3rd and 28th day (P < 0.05). Furthermore, significant differences of worm numbers between infected and control group was found on the 14th and 28th day (P < 0.001). An inverse correlation betwee the IgG levels and the resistance to re-infection was also observed (r = -0.948, P = 0.004), indicating that the resistance to reinfection is highly associated with the levels of IgG during the early phase of infection, and then with the IgM and IgE.

Serodiagnostic applicability of recombinant antigens of Clonorchis sinensis expressed by wheat germ cell-free protein synthesis system

We evaluated the diagnostic applicability of recombinant proteins from Clonorchis sinensis, the human liver fluke. Four recombinant proteins, 7-kDa protein (Cs7P), 28-kDa cysteine protease (Cs28CP), and 26- and 28-kDa glutathione s-transferases (Cs26GST and Cs28GST), were expressed by wheat germ cell-free protein synthesis system. In ELISA, crude antigen showed the highest sensitivity (92.7%). However, sensitivities of r7P (47.3%), r28CP (30.9%), r26GST (21.8%), and r28GST (14.5%) were dramatically lower. The overall specificities of the crude antigen, r7P, r28CP, r26GST, and r28GST, were 100%, 94.5%, 96.7%, 94.5%, and 98.9%, respectively. Taken together, r7P and r28CP showed moderate sensitivities and high specificities, whereas r26GST and r28GST revealed low sensitivities and high specificities. We demonstrated that recombinant antigens, when used as a single antigen for ELISA, are not sensitive enough to diagnose clonorchiasis. Cocktail or chimeric antigens may be useful to increase the sensitivity of each antigen and may improve the serodiagnosis of clonorchiasis.

Changing patterns of serum and bile antibodies in re-infected rats with Clonorchis sinensis

Rats develop strong resistance to re-infection and super-infection by Clonorchis sinensis. The present study investigated the antibodies present in the sera and bile juice of rats that were primary infected and re-infected with C. sinensis. The serum level of specific IgG antibodies, which were elevated 2 wk of the primary infection, peaked at 4 wk and subsequently remained unchanged even during re-infection. The total IgE level in serum increased slowly from 388 ng / ml to 3,426 ng / ml beginning 2 wk after the primary infection, and remained high up to 8 wk but dropped to a normal level (259 ng / ml) after treatment. In resistant re-infected rats, the serum IgE level increased rapidly and peaked within 1 wk, whereas no increase was observed in immunosuppressed rats. The serum level of specific IgA antibodies was elevated beginning 1 wk after infection, and decreased 4 wk after treatment. The total bile IgA level unchanged during the primary infection but increased in treated and re-infected rats. The elevated levels of serum IgE and bile IgA indicate that these immunoglobulins may be correlated with the development of resistance to re-infection by C. sinensis in rats.

Clonorchis sinensis: development and evaluation of a nested polymerase chain reaction (PCR) assay

Clonorchis sinensis is a fish-borne trematode endemic to East Asia, which infects over 35 million people globally. In the study described here, we developed a nested polymerase chain reaction (PCR) method for the specific and reliable detection of C. sinensis. The primers designed from the nucleotide sequence data derived in this study were evaluated for their specificity and sensitivity for the detection of C. sinensis. The specific amplification products were obtained only with C. sinensis and no amplifications occurred with the DNA of closely related trematodes including Opisthorchis viverrini demonstrating the specificity of the assay. The novel PCR method described here will be useful for the quarantine of fishery products and evaluation of transmission status of clonorchiasis in the endemic areas.

Organ-specific antigens of Clonorchis sinensis

This study was carried out to find out specific proteins from different organs of Clonorchis sinensis. Crude extract, organ-specific and excretory-secretory (ES) proteins were analyzed by immunoblot with infected human sera. The bands of 7- and 17-kDa were main component of intestinal fluid and ES protein and commonly found in all organspecific proteins. The 17-kDa protein was observed from ES antigen, intestinal fluid, eggs and sperms, 26- and 28-kDa proteins were from the uterus, vitellaria, and ovary, and 34-, 37-, 43- and 50-kDa proteins were mainly from the testis and sperms. Serum of mice immunized with sperms reacted to the 50-kDa protein by immunoblotting and immunohistochemical staining showed a positive reaction at the seminal receptacle and seminiferous tubule. The present results show that the 7-kDa protein is a common antigen of every part or organ of C. sinensis, but different organs express their specific antigenic protein bands.

The identification of a Clonorchis sinensis gene encoding an antigenic egg protein

The cDNA library of Clonorchis sinensis was screened for genes encoding antigenic proteins by using sera from clonorchiasis patients. A gene of 888 bp encoding a 28-kDa protein (Cs28) was cloned and found to contain a high percentage of glycine (20%), tyrosine (11%), and lysine (11%). The amino acid sequence of Cs28 showed 60% homology with the vitelline B precursor protein of Opisthorchis viverrini and of 33% homology with the vitelline B1 and B2 proteins of Fasciola hepatica. A strong positive reaction was observed in the intrauterine eggs of adult C. sinensis by immunohistochemical analysis using specific immune sera against recombinant Cs28 protein (rCs28). By immunoblot analysis, rCs28 displayed an antigenic reaction with 73% of the serum samples from 115 cases of clonorchiasis. In addition, it cross-reacted with the sera of 77.5% of 40 opisthorchiasis cases, 90% of 20 schistosomiasis cases, and 50% of 10 paragonimiasis cases. However, no cross-reactions were observed with the sera of sparganosis or cysticercosis patients. In conclusion, the Cs28 protein was identified as an egg protein of C. sinensis and as an antigen common to the trematode species examined.

Specific and common antigens of Clonorchis sinensis and Opisthorchis viverrini(Opisthorchidae, Trematoda)

The antigenic characterizations and serological reactions of human liver flukes, Clonorchis sinensis and Opisthorchis viverrini, were analyzed by immunoblot. The antigenic profiles of the crude extract of Clonorchis contained major proteins of 8, 26-28, 34-37, 43, and 70 kDa, and those of Opisthorchis 34-37, 43, 70, and 100 kDa. Of these, the 8, 26-28 and 34-37 kDa bands of Clonorchis and the 100 kDa of Opisthorchis were major components of each excretory-secretory antigen. The 8 and 26-28 kDa bands were specific to Clonorchis but the 100 kDa of Opisthorchis cross-reacted with the sera of clonorchiasis, and the 34-37, 70 and 100 kDa bands cross-reacted with sera of other helminthiases. The frequency and intensity of the immunoblot reactions were positively correlated with the intensity of the liver fluke infection.

Excretory-secretory antigen is better than crude antigen for the serodiagnosis of clonorchiasis by ELISA

Although stool examination is the standard diagnostic method of clonorchiasis, serodiagnosis by ELISA using crude antigen is now widely used because of its convenience. However, ELISA diagnosis still suffers from cross-reactions, and therefore there is a need to improve the present conventional ELISA. The present study was undertaken to evaluate the diagnostic value of ELISA using excretory-secretory antigen (ESA) instead of crude antigen (CA) of Clonorchis sinensis. The diagnostic sensitivity of ELISA using excretory-secretory antigen was 92.5%, which was higher than that of ELISA using crude Clonorchis sinensis antigen (88.2%). In addition, the specificity of excretory-secretory antigen was found 93.1% while that of crude antigen was 87.8%. In summary, Clonorchis sinensis ESA was found to be a better serodiagnostic antigen than CA for ELISA.

Expression of cysteine proteinase of Clonorchis sinensis and its use in serodiagnosis of clonorchiasis

A gene encoding cysteine proteinase from Clonorchis sinensis has been cloned and expressed in Escherichia coli. The cysteine proteinase cDNA fragment was amplified by reverse transcription-polymerase chain reaction using degenerate oligonucleotide primers derived from conserved active site of cysteine proteinases. The 5' and 3' regions of the gene were amplified using rapid amplification of cDNA ends. The cloned gene has an open reading frame of 696 bp and deduced amino acid sequence of 232. Sequence analysis and alignment showed significant homologies with the eukaryotic cysteine proteinases and conservation of the Cys, His, and Asp residues that form the catalytic triad. Analysis of the expressed protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the molecular weight of the protein was approximately 28.5 kDa. Proteolytic activity of the expressed protein was inhibited by cysteine proteinase inhibitors such as L-trans-epoxysuccinyl-leucylamide-(4-guanidino)-butane, iodoacetic acid, and leupeptin. The expressed protein showed biochemical properties similar to those of cysteine proteinases of other parasites. The expressed protein strongly reacted with the sera from patients with clonorchiasis but not with the sera from patients with paragonimiasis, fascioliasis, cysticercosis, and sparganosis, or with sera from normal human controls. These results suggest that the expressed protein may be valuable as a specific diagnostic material for the immunodiagnosis of clonorchiasis.

Purification and characterization of a 7-kDa protein from Clonorchis sinensis adult worms

A 7-kDa protein was purified from extracts of adult Clonorchis sinensis by a combination of ammonium sulfate precipitation, anion exchange chromatography, cation exchange chromatography, gel-filtration chromatography, and reversed-phase FPLC. The 7-kDa protein exists in the excretory-secretory products of adult C. sinensis, but not in extracts of adult Paragonimus westermani. Also, the 7-kDa protein reacted with the sera of patients with clonorchiasis but not with paragonimiasis or normal human sera. To observe the localization of the 7-kDa protein in the tissue of adult C. sinensis, an immunogold labeling method was followed using anti-7-kDa antibody. The gold particles were observed in the basal layer below the tegumental syncytium, in the interstitial matrix of the parenchyma, and in the content of the uterus. The 7-kDa cDNA was obtained through reverse transcription-polymerase chain reaction using a primer designed from N-terminal sequence analysis. Rapid amplification of cDNA ends (5'-RACE) was used to obtain the complete protein coding sequence. The sequence encodes a 90-amino acid polypeptide. The deduced amino acid sequence of the 7-kDa protein revealed no homology with proteins of different organisms reported so far. These results suggest that the 7-kDa protein is a fluid antigen and may be valuable as a tool for the immunodiagnosis of clonorchiasis.

Characterization of partially purified 8 kDa antigenic protein of Clonorchis sinensis

The 8 kDa antigenic protein of Clonorchis sinensis was partially purified by ammonium sulfate precipitation and subsequently by a column chromatographic steps. The purified protein was separated into 7 and 8 kDa protein bands through SDS-tricine gel electrophoresis, while the protein was found to migrate to a 8 kDa band in 7.5-15% SDS-PAGE. The molecular weight of the antigen was estimated to be 110 kDa by Superose 6 HR 10/30 gel filtration. The purified antigen strongly reacted with the human sera of clonorchiasis. The hyperimmune sera of BALB/c mice immunized against the 8 kDa protein were reacted with both the crude extract and the excretory-secretory product of adult worms, but not with the metacercarial extract. Immunohistochemical staining demonstrated that the protein was distributed to the tegument and subtegumental cells and also to the seminal receptacle. The present findings suggest that the 8 kDa protein is a partition of the multicomplex protein originating from various organs of adult C. sinensis, and that it is composed of several 7 and 8 kDa proteins.

Antigenic profile and localization of Clonorchis sinensis proteins in the course of infection

In the course of Clonorchis sinensis infection, antigens presented to the hosts may be in a close relation to growth of the fluke. The antigenic proteins stimulating IgG antibody production were chronologically identified by immunoblot and localized by immunohistochemical staining. In the early stage of infection until 12 weeks post-infection (PI), antigens were proteins with molecular mass larger than 34 kDa which were derived from the tegument, testes and intrauterine eggs. After 20 weeks PI, antigens recognized were 29, 27 and 26 kDa proteins from the intestine, excretory bladder and reproductive organs. It is suggested that the tegumental proteins are the most potent antigens and the excretory-secretory proteins with middle molecular mass of 26-45 kDa contribute to the high level production of antibodies after 20 weeks of the C. sinensis infection.

Shared epitope for monoclonal IR162 between Anisakis simplex larvae and Clonorchis sinensis and cross-reactivity between antigens

IR162 is a rat monoclonal IgE antibody (mAb). In the investigation of rat IgE production, the antigens recognized by IR162 (IR-Ags) were found to be expressed by a variety of helminthic parasites. By western blot analysis, IR162 detected bands in crude extracts of Anisakis simplex larvae, Clonorchis sinensis, Paragonimus westermani, plerocercoids of Spirometra mansoni, and Toxocara canis. Excretory-secretory material from A. simplex larvae also contained a protein recognized by IR162. IR162 mAb obtained from both Serotec and Zymed recognized identical bands of A. simplex larvae. Sandwich enzyme-linked immunosorbent assay analysis indicated that both IR-Ags of A. simplex larvae (IR-As) and C. sinensis (IR-Cs) were important antigens with respect to induction of specific IgG in human infections with these 2 organisms. Even though minimal cross-reaction between IR-As and IR-Cs was observed using sera from infected individuals, these results indicate that IR-Ags are found in the parasites examined, that IR-As and IR-Cs are the antigens that induce specific antibody in natural infection, and that the epitope that binds IR162 is shared by A. simplex larvae and C. sinensis.

Molecular cloning and immunological characterization of phosphoglycerate kinase from Clonorchis sinensis

The parasite Clonorchis sinensis was determined to utilize a large amount of external glucose to carry its energy metabolism. Phosphoglycerate kinase (PGK), a glycolytic enzyme, found in many parasites, has been identified as one of the candidate molecules distinguished from human counterparts for vaccine and drug developments. A cDNA clone purified by screening a C. sinensis cDNA library using a heterologous cDNA probe encoded a putative peptide of 415 amino acids with over 60% identities with PGKs from a number of animals. The putative peptides revealed domains corresponding to 12 beta-sheets and inner loops forming a substrate-binding cleft of animal PGKs. The gene product was overexpressed in Escherichia coli and showed a PGK-like enzyme activity. A polyclonal antibody raised against the recombinant C. sinensis PGK was specific to native C. sinensis PGK and localized it to the muscular tissue and tegument of the adult flukes. The C. sinensis PGK elicited antibodies in C. sinensis-infected rabbits. Therefore, it is proposed that C. sinensis PGK could be used as an immunoreagent in the serodiagnosis for clonorchiasis.

Usefulness of IgG4 subclass antibodies for diagnosis of human clonorchiasis

The present study analyzed serum IgG subclass antibody reaction to major antigenic bands of Clonorchis sinensis to investigate improvement of its serodiagnosis. Of the four subclass antibodies, IgG1 and IgG2 antibodies were produced but not specific, IgG3 antibody was least produced, and IgG4 antibody was prominent and specific. The serum IgG antibody reaction to any of 43-50, 34-37, 26-28, and 8 kDa bands was found in 65.5% of 168 egg positive cases while IgG4 antibody reaction was found in 22.0% of them. The positive rates of IgG and IgG4 antibodies were directly correlated with the intensity of infection. All of the sera from heavily infected cases over EPG 5,000 showed positive reaction for specific IgG and IgG4 antibodies. The specific serum IgG4 antibody disappeared within 6 months after treatment. The bands of 35 kDa and 67 kDa cross-reacted with IgG antibodies but not with IgG4 antibodies in sera of other trematode infections. The present findings suggest that serum IgG4 antibody reaction to 8 kDa band is specific but not sensitive. Any method to increase its sensitivity is required for improved serodiagnosis.

Immunodiagnosis of clonorchiasis using a recombinant antigen

A cDNA expression library of Clonorchis sinensis adult worm was constructed, and screened out immunologically. One clone, pBCs31, was selected in view of its predominant reactivity with an experimentally infected rabbit serum. Recombinant C. sinensis antigen with 28 kDa as a beta-galactosidase fusion protein produced in Escherichia coli was identified by immunoblot analysis. The cloned gene was composed of 16 copies of a 30 base pair repeat and an additional 320 bases. The deduced amino acid sequence of the tandem repeat was AQPPKSGDGG. On RNA slot blot analysis. C. sinensis adult worm RNA showed a positive reaction with the cloned gene. Enzyme-linked immunosorbent assay using a purified recombinant antigen of pBCs31 showed high specificity for diagnosis of clonorchiasis.

A Clonorchis sinensis-specific antigen that detects active human clonorchiasis

A Clonorchis sinensis-specific antigen in excretory-secretory product of C. sinensis (CsE) was assessed in human clonorchiasis by immunoblot. Thirty and 7 kDa antigens of CsE2, one of four different batches of CsEs reacted strongly with infection sera from clonorchiasis patients; however, the antigens reacted weakly with 6-month post-treatment sera from praziquantel-cured cases, but were still highly detected by the sera from praziquantel-failed patients, indicating that the 30 and 7 kDa antigens can detect antibodies during an active infection. The 30 kDa antigen showed some cross reactions with sera from patients with Paragonimus westermani and Metagonimus yokogawai, while the 7 kDa antigen did not, suggesting that the 7 kDa antigen has high specificity. The 30 kDa antigen reacted with some past clonorchiasis sera, whereas the 7 kDa antigen did not, supporting that antibodies to the 7 kDa antigen are not present in sera from past clonorchiasis patients. In an endemic area, 92% (23/25) of active clonorchiasis patients and 91% (10/11) of mixed infection patients with C. sinensis and M. yokogawai had IgG antibodies to the 7 kDa antigen, while 40% (6/15) of past clonorchiasis individuals and 43% (3/7) of metagonimiasis patients cross-reacted to the antigen. These data suggest that the 7 kDa antigen in an excretory-secretory antigen may serve as a marker of an active clonorchiasis with reliable specificities in past clonorchiasis, paragonimiasis and metagonimiasis.