Inflammatory responses to microbial products are amplified by a pathway mediated by triggering a receptor expressed on the myeloid cells (TREM)-1. Relatively a few studies have been performed to investigate the role of TREM-1 in macrophage activation in response to parasitic infection. In this study, we delineate the role of the innate immunoreceptor TREM-1 in the parasite Schistosoma mansoni infection model from early to late (chronic) phases of infection. Flow cytometry analysis revealed gradual increase in the production of TREM-1 protein on CD11b(+) myeloid cells, with maximum production at 5 weeks p.i. Similar results in the pattern of TREM-1 mRNA expressions in splenic CD11b(+) cells from infected mice were obtained by real-time PCR. However, unlike in spleen, the TREM-1 mRNA expression in liver tissue showed no significant increase throughout the infection, including periods of maximum production of parasite eggs. Administration of schistosoma egg homogenate antigen to stimulate J774A.1 cells inhibited TREM-1 expression on the surface, indicating that some substances of the Schistosma eggs may inhibit the expression of TREM-1 on macrophages, lowering the macrophage-mediated inflammatory response of infected hosts.
Schistosoma japonicum obtained from Taiwan is a zoophilic strain that only infects domestic and small animals. Recombinant fructose-1,6-bisphosphate aldolase (FBPA) derived from this strain was used as an antigen in an enzyme-linked immunosorbent assay (ELISA) for the diagnosis of human schistosomiasis. The full-length DNA sequence of FBPA was found to be 1092 bp, encoding a protein of 363 amino acid residues, with a molecular mass of 39.6 kDa. A total of 120 participants were recruited from China and Taiwan to evaluate the diagnostic value of this recombinant protein. In these participants, 34 were found to be infected with S. japonicum, 16 with Ascaris lumbricoides, 15 with hookworm, 13 with Paragonimus westermani and 13 with Clonorchis sinensis, whereas 29 had no ova on faecal examination. Western blot analysis showed that the recombinant FBPA reacts strongly with schistosome ova-positive sera. The sensitivity and specificity of ELISA with FBPA were found to be 85.3% and 93.0%, respectively. These results indicate that FBPA derived from the Formosan strain of S. japonicum can be used for the diagnosis of human schistosomiasis.
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