Characterization of a major surface-associated excretory-secretory antigen of Trichinella spiralis larvae with antibodies to keyhole limpet haemocyanin

Application of DNA-based diagnostics in detection of schistosomal DNA in early infection and after drug treatment

BACKGROUND

Research is now focused on identification of sensitive and specific diagnostic tests for early identification of schistosomal infection and evaluation of chemotherapy in field situations in China.

RESULTS

This study compared loop-mediated isothermal amplification (LAMP) with conventional PCR as DNA-based diagnostic techniques for the early detection of schistosomal DNA and the evaluation of chemotherapy. The results showed that both PCR and LAMP assays targeting a 301 base pair (bp) sequence of the highly repetitive retrotransposon, SjR2, amplified DNA from schistosomes but were unable to distinguish between schistosome species. LAMP and conventional PCR were shown to amplify the target sequence of the SjR2-pCR2.1 recombinant plasmid template with limits of detection of 10⁻⁴ ng and 10⁻² ng, respectively, thus demonstrating the superior sensitivity of the LAMP method. Schistosoma japonicum DNA was detected in all serum samples obtained from the three experimental groups at 1 week post-infection by LAMP assay, while the rate of detection by conventional PCR ranged from 50% to 66%. The potential application of PCR and LAMP assays for the evaluation of artesunate and praziquantel chemotherapy was investigated. PCR was shown to be less sensitive for detection of schistosomal DNA in drug-treated rabbit sera than the LAMP method.

CONCLUSIONS

The data presented here indicate that LAMP is suitable for the detection of early infection in the groups primarily infected with Schistosoma japonicum, such as migrants, travellers, military personnel and the younger age groups. However, it is less suitable for evaluation of the efficacy of chemotherapy in the early stages because of its high sensitivity.

Development of a new assay for the diagnosis of schistosomiasis, using cercarial antigens

We have developed a new ELISA for detection of anti-schistosome antibodies using an extract from Schistosoma mansoni cercariae. We evaluated the new assay on serum samples sent to the Hospital for Tropical Diseases, Department of Clinical Parasitology, London, UK, by comparing it with our routinely used S. mansoni soluble egg antigen (SEA) assay. We also evaluated the new assay for cross-reactivity with a number of helminth and other infections. We demonstrate that the cercarial antigen assay is equivalent to the SEA assay for serodiagnosis of schistosomiasis in a non-endemic setting. The cercarial antigen preparation is more easily produced than SEA, and for this reason this assay may be preferred for routine clinical use and may be amenable to scaling up. Further assessment is needed before it can be recommended for use in an endemic area, as chronic disease and co-infection with other helminths are likely to be under-represented in our sample set.

Secretion of IL-12 by murine macrophages activated by immunoglobulin receptor-mediated internalization of the surface coat of Trichinella spiralis larvae

Trichinella spiralis larvae incubated with a rabbit antiserum raised against the larval surface coat bound murine macrophages to the parasite surface. Cell binding was not observed without the antisurface coat serum, or with incubation of larvae in normal rabbit serum, or with antibodies to keyhole limpet haemocyanin which identify a cryptic T. spiralis larval antigen. Cell adherence to the larval surface was lost by treatment of the cells with the lysosomotropic drug primaquine, implicating a receptor-mediated mechanism. Cells adhering to the parasite surface internalized parasite surface coat material, which was subsequently concentrated into endosomes. Culture supernatants from these cells contained enhanced levels of IL-12. Thus, the initial Th1 response to T. spiralis infection may be explained by these data.

Role of steroid hormones in Trichinella spiralis infection among voles

Males are generally more susceptible to parasite infection than females. This sex difference may reflect the suppressive effects of testosterone and enhancing effects of estradiol on immune function. This study characterized the role of circulating steroid hormones in sex differences after infection with the nematode Trichinella spiralis. Because testosterone suppresses immune function and because polygynous males have higher circulating testosterone concentrations than monogamous males, sex differences in parasite burden were hypothesized to be exaggerated among polygynous meadow voles compared with monogamous prairie voles. As predicted, sex differences in response to T. spiralis infection were increased among meadow voles; males had higher worm numbers than females. Male and female prairie voles had equivalent parasite burden. Overall, prairie voles had higher worm numbers than meadow voles. Contrary to our initial prediction, differences in circulating estradiol concentrations in females, testosterone concentrations in males, and corticosterone concentrations in both sexes were not related to the observed variation in T. spiralis infection. Taken together, these data suggest that not all sex differences in parasite infection are mediated by circulating steroid hormones and that adaptive-functional explanations may provide new insight into the causes of variation in parasite infection.

Cross reacting antibodies against keyhole limpet haemocyanin may interfere with the diagnostics of acute schistosomiasis

The number of individuals catching schistosomiasis has increased with the popularity of 'primitive tourism' in Africa. Highly immunogenic material originating from the intestine of intravascular adult schistosomes gives rise to an antibody response making possible early identification of infected individuals using serology. Antibodies against gut associated antigens (anti-GAA), detected by indirect immunofluorescence microscopy employing sections of adult worms as antigen may occur before the onset of egg production. In the present study we show that this well known schistosomiasis-specific anti-GAA staining reaction can be confused with a similar staining reaction with ducts of both male and female worms. Antibodies with duct reactivity were seen in sera both from schistosomiasis-patients and patients with some other invasive worm infections. Cross reactive anti-duct antibodies appear to have different specificity. One cross reactive antibody reacted with antigenic epitopes present in keyhole limpet haemocyanin (KLH). Anti-duct reactivity could be inhibited by absorption with KLH. This was most obvious in the trichinellosis patient sera.

A role for second messengers in the control of activation-associated modification of the surface of Trichinella spiralis infective larvae

The involvement of second messengers in the control of activation-induced changes to the surface of Trichinella spiralis infective larvae was investigated using membrane-permeant photo-activatable 'caged' compounds to alter intracellular levels of inositol trisphosphate (IP3), calcium ions (Ca2+) and cyclic AMP (cAMP). Activation of larvae by incubation in culture medium containing trypsin and bile was followed by the loss of the surface coat labelled with the fluorescent PKH26 lipid probe and this correlated with the reciprocal acquisition of surface lipophilicity detected using the fluorescent lipid probe octadecanoyl aminofluorescein (AF18). Optimal surface coat shedding and AF18 insertion was also achieved following photolysis of caged mediators liberating IP3, Ca2+ or cAMP within the parasite. Chelation of Ca2+, however, abolished the effects of larval activation. Nevertheless, addition of cAMP (but not IP3) to Ca(2+)-depleted larvae overcame this inhibition and restored AF18 insertion to levels achieved by activated parasites. Therefore, the existence of a linear second messenger pathway involving the sequential release of IP3, Ca2+ and then cAMP is likely.