Suppression of adaptive immunity to heterologous antigens by SJ16 of Schistosoma japonicum.
ABSTRACT Despite the great effort that has been given to control the disease, schistosomiasis remains the most important human helminth infection in terms of morbidity and mortality. Natural infection of schistosomes induces very little protective immunity against reinfection. Moreover, effective schistosome vaccines for practical use have not been developed. These parasites appear to have evolved highly effective modulatory mechanisms on their host's immune system that promote the parasites' survival and also hinder the development of effective strategies for treatment of the disease. Understanding of the mechanisms of schistosome-mediated immune modulation would be most helpful in schistosomiasis prevention and control. Previously, we have identified from Schistosoma japonicum an anti-inflammatory protein, Sj16, which suppresses thioglycollate-induced peritoneal inflammation in BALB/c mice, as well as thioglycollate-mediated peritoneal macrophage maturation, while modulating cytokine and chemokine production from peritoneal cells. In the present study, we have further investigated the modulatory effect of Sj16 on the host's adaptive immunity to heterologous antigens with the use of recombinant Sj16 (rSj16) expressed and purified from Escherichia coli . Results from this study indicate that rSj16 significantly suppresses antibody production, in addition to Th1 and Th2 responses to heterologous antigens in the BALB/c mouse model. Our study also reveals that rSj16 suppresses lipopolysaccharide-induced major histocompatibility complex II expression and IL-12 production, while increasing IL-10 production in resident peritoneal macrophages. These results may partially explain why parasite-related antigens cannot mount a protective immunity during early stages of schistosome infection.
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ABSTRACT: Sj16, a 16-kDa protein secreted from Schistosoma japonicum, has been demonstrated an anti-inflammatory effect in vitro and in vivo, but its mechanism is still not clear. In this study, microarray analysis was performed to investigate the effects of recombinant Sj16 (rSj16) on the gene expression of the lipopolysaccharide (LPS)-stimulated dendritic cells (DCs). Immature DCs were treated with LPS, LPS + recombinant Sj16 (rSj16), or rSj16 alone for 24 h, and the gene expression profiles were examined using complementary DNA (cDNA) microarrays. With the cutoff value of 2-fold change in the expression, 509 genes were affected, 226 genes upregulated, and 283 genes downregulated after adding rSj16. Analysis by functional annotation clustering tool showed that rSj16-affected genes mainly associated with inflammatory response, defense response, regulation of immune system process, apoptosis, and cell migration. The results revealed that rSj16 reduced the LPS-induced pro-inflammatory genes such as cytokines (e.g., IL6, IL18, IFN-γ, IL12a, IL1b), chemokines, and receptors (e.g., CXCL1, CXCL9, CCL5, CCR5, CCR1, CCR2, CXCR3) and increased the anti-inflammatory gene IL-10. Further data mining of these genes by pathway analysis showed that genes regulated by rSj16 were significantly involved in cytokine-cytokine receptor interaction, NOD-like receptor signaling pathway, Toll-like receptor signaling pathway, antigen processing and presentation, and Jak-STAT signaling pathway. In addition, quantitative real-time PCR (qRT-PCR) and Western blot analysis showed that rSj16 downregulated the expression of inhibitor of nuclear factor kappa-β kinase subunit beta (IKKβ) and nuclear factor-kappa β p65 (NF-κβ) messenger RNA (mRNA) and inhibited the phosphorylation of IKKβ and the NF-κB p65 protein, which implied that rSj16 exerting immunomodulatory effects by suppressing NF-κB signaling pathway. These results provide useful information in further understanding of the immunoregulation mechanisms of Sj16, and it is indicated that Sj16 could be as a potential molecule for the immunosuppressant drug development.Parasitology research. 06/2014;