Kinetic Analysis Of Th17 Cells During Schistlsome Japonicum Infection In C57BL/6 Mice

Thelper (Th) cells express the CD⁴⁺antigen and can differentiate into at leasttwo subsets, Th1 and Th2 cells, distinguished by the array of cytokine genes thatthey express. Th1 cells secrete IL-2, IFN-γand TNF-α, which is important for theeradication of intracellular pathogens, including bacteria, parasites, yeasts andviruses; whereas Th2 cells secrete IL-4, IL-5, IL-6, IL-10, and IL-13 and can activatemast cells and eosinophils, thereby eradicating helminthes and other extracellularparasites. The development of Th1 versus Th2 cells is a major branch point in theimmune response. Th17 cells have recently emerged as a third independent T cellsubset that may play an essential role in protection against certain extracellularpathogens. Although the function of these cell subtypes is not completely elucidated,emerging data suggest that Th17 cells may play an important role in host defenceagainst extracellular pathogens, which are not efficiently cleared by Th1-type andTh2-type immunity. While these subsets have specific effector functions in clearinginfections, dysregulated expansion of CD⁴⁺ Th effector T cells may lead toimmunopathology. In addition to differentiate into Th1, Th2 and Th17 effectorsubsets, CD⁴⁺ T also could be induced to differentiate into CD⁴⁺CD²⁵⁺ Tregs withimmunosuppressive activity that down-regulate immune responsiveness therebyinhibiting immunopathology while promoting parasite survival by directly repressTh1, Th2 and Th17 cells induction and responses.Similar to Th1 and Th2 cells, Th17 cells require specific cytokines and transcription factors for their differentiation. A combination of TGF-βplus IL-6, andthe transcription factors RORγt and STAT3, were recently described to be essentialfor initial differentiation of Th17 cells, IL-21 for the amplification of the Th17 cellsand IL-23 for the later stabilization of the Th17 cell subset. Both IFN-γand IL-4antagonize the development of Th17 cells. Foxp3 induction restrains thedifferentiation of inflammatory Th17 cells in response to TGF-βin the absence ofother proinflammatory cytokines by inhibiting the activity of RORγt.Schistosoma japonicum has provided excellent models for studying theinduction and regulation of Th1 and Th2 cell subsets responses to infection. Recently,emerging data suggest that IL-17, but not IFN-γ, is the CD⁴⁺ T cell-derived cytokinemost directly associated with the severity of hepatic granulomatous inflammation,indicating that an IL-17-producing T cell is a major force behind severe pathology inschistosomiasis. However, there is very little data available to show the immuneresponse induced by Th17 cell against infection at the early-stage of the S. japonicuminfection and whether their cytokine IL-17 mediated the host protective immunity.In the present study, we investgated the Kinetics of the percentages of Th17,Th1,Th2 and Treg cells in total CD⁴⁺ T cells during different stages of infection. Wealso detected the levels of IL-17,IFN-γ,IL-4,TGF-β,IL-6,IL-21å’ŒIL-23 whichmost directly associated with the differentiation of Th17 cells. Then we investgatedthe percentages of Th17,Th1,Th2 and Treg cells in total CD⁴⁺ T cells and therelated above cytokines from the mice immunized with SEA,SWA or PBS. At last,by using administration of recombinant murine IL-17 (rmIL-17) or anti-IL-17neutralizing mAb we investigated the role of IL-17 in protective immunity against S.japonicum infection.The main results we got are as follows:1. During infection, the proportion of Th17 cells in CD⁴⁺ T cells was slightlyincreased in 3-5 weeks post-infection if compared to that before infection (0week), and significantly increased after 5 weeks post-infection. Meanwhile, theproportion of Th1,Th2 cells in CD⁴⁺ T cells was also increased. However, during first three weeks post-infection, the proportion of Th1 cells rose much morequickly than Th2 cells did, suggesting that there is a Th1-biased response due tonon-egg antigens that occurs before the schistosomes lay eggs. In contrast, aftereggs deposition, the number of Th2 cells continued to increase rapidly, while thenumber of Th1 cells reached a platform and almost stopped increasing sinceeight weeks post-infection, suggesting that the egg antigen induces a Th2-biasedresponse. The proportion of Treg cells in CD⁴⁺ T cells was increased more rapidlyduring the chronic phase of infection.2. To further determine the impact of different antigens on the production of Th17cells. We immunized the C57BL/6 mice with SEA, SWA or PBS. Results showedthat significantly higher levels of Th17 cells were only observed in the SEA group,suggesting that repeated vaccinations of the SEA preferentially induced the Th17cells.3. By administration of rmIL-17 or anti-IL-17 neutralizing mAb, we investigated therole of IL-17 in protective immunity against S. japonicum infection. Resultssuggested that IL-17 might not affect to induce the effective protective immunity.Although the levels of cytokines that had been proved by many studies to besuppressive to the differentiation of Th17 cells are mostly upregulated, but thatseems to have no significant effects on the suppression of Th17 cells generation.However, according to our study, it is not clear yet how this process occurs.