Toll-Like Receptor Gene Expression during Trichinella spiralis Infection

In Trichinella spiralis infection, type 2 helper T (Th2) cell-related and regulatory T (T(reg)) cell-related immune responses are the most important immune events. In order to clarify which Toll-like receptors (TLRs) are closely associated with these responses, we analyzed the expression of mouse TLR genes in the small intestine and muscle tissue during T. spiralis infection. In addition, the expression of several chemokine- and cytokine-encoding genes, which are related to Th2 and T(reg) cell mediated immune responses, were analyzed in mouse embryonic fibroblasts (MEFs) isolated from myeloid differentiation factor 88 (MyD88)/TIR-associated proteins (TIRAP) and Toll receptor-associated activator of interferons (TRIF) adapter protein deficient and wild type (WT) mice. The results showed significantly increased TLR4 and TLR9 gene expression in the small intestine after 2 weeks of T. spiralis infection. In the muscle, TLR1, TLR2, TLR5, and TLR9 gene expression significantly increased after 4 weeks of infection. Only the expression of the TLR4 and TLR9 genes was significantly elevated in WT MEF cells after treatment with excretory-secretory (ES) proteins. Gene expression for Th2 chemokine genes were highly enhanced by ES proteins in WT MEF cells, while this elevation was slightly reduced in MyD88/TIRAP(-/-) MEF cells, and quite substantially decreased in TRIF(-/-) MEF cells. In contrast, IL-10 and TGF-β expression levels were not elevated in MyD88/TIRAP(-/-) MEF cells. In conclusion, we suggest that TLR4 and TLR9 might be closely linked to Th2 cell and T(reg) cell mediated immune responses, although additional data are needed to convincingly prove this observation.