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

Anomalous immunogenic properties of serine proteases

It has previously been shown that a approximately 27 kDa serine protease of Schistosoma mansoni larvae, the cercarial elastase (CE), was a poor immunogen in as much as it failed to induce an antibody response. The CE has a critical role in enabling schistosome larvae to penetrate the skin of their definitive hosts, so the apparently poor immunogenicity of this enzyme is clearly of interest. To understand its lack of immunogenicity better and in particular to determine whether it is related to its proteolytic activity, we have measured antibody responses of mice to three different serine proteases. Groups of mice were immunized with porcine pancreatic trypsin (TRY), chymotrypsin (CHY) or elastase (ELA) and the resulting antibody response compared with antibody responses to two non-protease antigens, chicken egg albumin (OVA) and Schistosoma japonicum glutathione S-transferase (GST), all being administered with alum as an adjuvant. Of 12 mice that were injected five times at 14 day intervals with TRY, only one produced antibody reactive with this enzyme in ELISA. Immunizations with CHY or ELA induced somewhat better antibody responses than TRY, but the responses to the first and second injections of these two proteases nevertheless seemed comparatively lower than the responses to GST. Induction of antibody responses by OVA and GST was not affected when TRY was injected concomitantly. Thus, the antibody response to one of the serine proteases used in this study, mammalian trypsin, was anomalous.

The immune response of rats to vaccination with the cDNA or protein forms of the cysteine proteinase of Fasciola hepatica

Our previous experiments have shown that intramuscular injection of Sprague-Dawley rats with a pcDNA 3.1 vector carrying cDNA encoding for a cysteine proteinase (CP) of F. hepatica may induce a high level of protection against subsequent infection with F. hepatica metacercariae (mc). The aim of the present study is to compare the immune response of Sprague-Dawley rats vaccinated intranasally with plasmid containing cDNA of CP of the fluke and intramuscularly or intraperitoneally with the recombinated enzyme protein to challenge with fluke metacercariae. In addition, protection following intranasal DNA vaccination was evaluated. Two experiments were carried out. In the first experiment rats were vaccinated twice with 50microg of cDNA containing plasmid or with 100microg protein of recombinated CP. Three weeks after the second vaccination rats were challenged orally with 25 mc. On days 0, 21, 42 and 63 after the challenge blood samples were collected for the evaluation of white blood cell, eosinophil and specific antibody responses. During the second experiment groups of five male and female rats were vaccinated twice intranasally with CPcDNA then challenged with 30 mc and dissected 5 weeks later. Results obtained in the experiments suggested that intranasal immunisation of rats with CPcDNA seems to favour a Th2 regulated antibody response. Intramuscular or intraperitoneal injections of CP protein stimulate both Th1 and Th2-dependent antibodies. Mean worm burdens found in rats vaccinated intranasally 5 or 10 weeks after the challenge were reduced by 61-75% in comparison with the challenge controls which suggests that intranasal vaccination with CPcDNA may protect hosts against F. hepatica infection.

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.

Clinical Features of Paragonimiasis Cases Recently Found in Japan: Parasite‐Specific Immunoglobulin M and G Antibody Classes

We retrospectively analyzed clinical features in 30 patients who were referred to our laboratory and given a diagnosis of Paragonimus westermani infection in 1999. Our results indicate that pleurisy with eosinophilia and dominant immunoglobulin (Ig) M antibody are characteristic features of the early stage of paragonimiasis, whereas IgG antibody is dominant in the late stage. Thus, in addition to tests for parasite-specific IgG antibody, tests for IgM-class antibody should always be considered for patients with pleurisy in whom paragonimiasis is suspected.

Structural and immunological characteristics of a 28-kilodalton cruzipain-like cysteine protease of Paragonimus westermani expressed in the definitive host stage

A complete cDNA sequence encoding a 28-kDa cruzipain-like cysteine protease of adult Paragonimus westermani, termed Pw28CCP, was isolated from an adult cDNA library. The cDNA contained a single open reading frame of 975 bp encoding 325 amino acids, which exhibited the structural motif and domain organization characteristic of cysteine proteases of non-cathepsin Bs including a hydrophobic signal sequence, an ERFNIN motif, and essential cysteine residues as well as active sites in the mature catalytic region. Analysis of its phylogenetic position revealed that this novel enzyme belonged to the cruzipain-like cysteine proteases. The sequence of the first 13 amino acids predicted from the mature domain of Pw28CCP was in accord with that determined from the native 28-kDa enzyme purified from the adult worm. Expression of Pw28CCP was observed specifically in juvenile and adult worms, with a location in the intestinal epithelium, suggesting that this enzyme could be secreted and involved in nutrient uptake and immune modulation. The recombinant protein expressed in Escherichia coli was used to assess antigenicity by immunoblotting with sera from patients with active paragonimiasis and from those with other parasitic infections. The resulting sensitivity of 86.2% (56 of 65 samples) and specificity of 98% (147 of 150 samples) suggest its potential as an antigen for use in immunodiagnosis.

Persisting antibody reaction in paragonimiasis after praziquantel treatment is elicited mainly by egg antigens

Antibody responses in serum and cerebrospinal fluid (CSF) samples from patients with active and chronic paragonimiasis and in sera from patients on whom follow-up studies were done after praziquantel treatment were analyzed using antigens of Paragonimus westermani prepared from eggs, metacercariae, juveniles of 4- and 7-week old, adult worms and recombinant protein of 28 kDa cruzipain-like cysteine protease (rPw28CCP). The patient sera/CSFs of active and chronic paragonimiasis revealed strong antibody reactions against the crude extracts of 4- and 7-week old juveniles as well as against those from egg and adult. rPw28CCP also showed specific reaction to the sera with active paragonimiasis. After the treatment, levels of specific antibodies in the sera gradually decreased to negative range in most patients. In some cases with persisting high antibody levels, however, the reactions at 27 kDa egg protein were sustained throughout the observation period of 34 months. The reactions at 35 and 32 kDa in adult extract and rPw28CCP disappeared rapidly after the treatment. Persistent antibody reactions even after successful treatment are provoked by continuous antigenic challenge from eggs which were not resolved by treatment.