<i>Clonorchis sinensis</i> adult-derived proteins elicit Th2 immune responses by regulating dendritic cells via mannose receptor

<div><p>Background</p><p><i>Clonorchis sinensis</i> (<i>C</i>. <i>sinensis</i>) is the most widespread human liver fluke in East Asia including China and Korea. Clonorchiasis as a neglected tropical zoonosis, leads to serious economic and public health burden in China. There are considerable evidences for an etiological relation between chronic clonorchiasis and liver fibrosis in human beings. Liver fibrosis is a highly conserved and over-protected response to hepatic tissue injury. Immune cells including CD4⁺ T cell as well as dendritic cell (DC), and pro-fibrogenic cytokines like interleukin 4 (IL-4), IL-13 have been identified as vital manipulators in liver fibrogenesis. Our previous studies had a mere glimpse of T helper type 2 (Th2) dominant immune responses as key players in liver fibrosis induced by <i>C</i>. <i>sinensis</i> infection, but little is known about the involved mechanisms in this pathological process.</p><p>Methodology/Principal findings</p><p>By flow cytometry (FACS), adult-derived total proteins of <i>C</i>. <i>sinensis</i> (<i>Cs</i>TPs) down-regulated the expression of surface markers CD80, CD86 and major histocompatibility complex class II (MHC-II) on lipopolysaccharide (LPS) induced DC. ELISA results demonstrated that <i>Cs</i>TPs inhibited IL-12p70 release from LPS-treated bone marrow-derived dendritic cells (BMDC). IL-10 level increased in a time-dependent manner in LPS-treated BMDCs after incubation with <i>Cs</i>TPs. CD4⁺ T cells incubated with LPS-treated BMDCs plus <i>Cs</i>TPs could significantly elevate IL-4 level by ELISA. Meanwhile, elevated expression of pro-fibrogenic mediators including IL-13 and IL-4 were detected in a co-culture system of LPS-activated BMDCs and naive T cells containing <i>Cs</i>TPs. <i>In vivo</i>, <i>Cs</i>TPs-immunized mice enhanced expression of type 2 cytokines IL-13, IL-10 and IL-4 in both splenocytes and hepatic tissue. Exposure of BMDCs to <i>Cs</i>TPs activated expression of mannose receptor (MR) but not toll like receptor 2 (TLR2), TLR4, C-type lectin receptor DC-SIGN and Dectin-2 on the cell surface by RT-PCR and FACS. Blockade of MR almost completely reversed the capacity of <i>Cs</i>TPs to suppress LPS-induced BMDCs surface markers CD80, CD86 and MHC-II expression, and further made these BMDCs fail to induce a Th2-skewed response as well as Th2 cell-associated cytokines IL-13 and IL-4 release <i>in vitro</i>.</p><p>Conclusions/Significance</p><p>Collectively, we validated that <i>Cs</i>TPs could suppress the maturation of BMDCs in the presence of LPS via binding MR, and showed that the <i>Cs</i>TPs-pulsed BMDCs actively polarized naive T helper cells to Th2 cells though the production of IL-10 instead of IL-12. <i>Cs</i>TPs endowed host with the capacity to facilitate Th2 cytokines production including IL-13 and IL-4 <i>in vitro</i> and <i>vivo</i>. The study might provide useful information for developing potential therapeutic targets against the disease.</p>