Gr-1+MDSC样细胞在宿主抗衣原体呼吸道感染中的作用及作用机制

Chlamydia infection is a serious public-health problem worldwide. So far, no vaccine is available to prevent human chlamydial dieases due to the lack of clear understanding of immune mechanisms to chlamydial infections. Chlamydial infection is accompanied by significant infiltration of neutrophils at the site of infection. It has been reported that neutrophils are able to destroy chlamydiae in vitro. However, the in vivo role of PMNs in host defense against C. muridarum infection is still controversial, and the underlying mechanisms by which PMNs cells modulate immune response during C. muridarum infection is largely unknown. Our preliminary experiment showed that the Gr-1+ cells accumulating during infection can be divided into Gr-1hi and Gr-1int subpopulations. The percentage of each subset are significantly different between a resistant strain C57BL/6 mice and a susceptible strain C3H/HeN mice following C. muridarum infection. To date , studies identify the influx of neutrophils based on simply measuring “Gr1-positive” cells, but clearly our current concept needs to be significantly modified because Gr-1 Ab RB6-C85 recognizes both Ly6G and Ly6C epitopes. Based on the observation that higher neutrophil infiltration is not always associated with better protection, and they share surface markers with MDSC，we assume that Chlamydia infection induce Gr-1+ MDSC-like cell accumulation at infect site AND/OR in the peripheral lymphoid tissues, which affect host sensibility to C. muridarum infection though turnning off the effective innate and adaptive immune response. On the basis of this hypothesis , in present study, we will explore the accumulation kinetics of Gr-1+ cell as well as its major subsets during C. muridarum lung infection and identify the morphologic, phenotypic and functional characteristics. Furthermore, By combining two different antibody blocking approaches and cell adoptive transfer strategy, we aim to determine the role of Gr-1+ cell in host defense against Chlamydia lung infection and to elucidate the mechanisms by which Gr-1+ cell influence host resistance to chlamydial lung infection. This study will gain insight on a better understanding of the defence mechanism to chlamydial infection, which has significant implications in chlamydial vaccine development and designing strategies.

衣原体感染伴随感染部位Gr-1+细胞大量浸润。目前关于Gr-1+细胞在宿主抗衣原体感染中作用的研究尚存在很多争议。Gr-1+细胞如何调控宿主抗衣原体免疫应答的机制也知之甚少。本课题组前期工作发现，衣原体感染诱导的Gr-1+细胞可分解为Gr-1hi和Gr-1int亚群，且Gr-1+细胞亚群构成的差异与C3H小鼠抗衣原体感染易感性的增加有关。结合近年来急慢性感染中髓系抑制细胞聚集及亚群功能研究的相关文献，我们猜测，衣原体感染可诱导Gr-1+MDSC样免疫抑制细胞在感染部位(和/或淋巴组织)的聚集，该细胞通过调节宿主抗衣原体免疫应答导致不同的感染结局。本课题将从解析Gr-1+细胞亚群构成的全新角度，阐明Gr-1+ MDSC样细胞在宿主抵抗衣原体感染中的作用及其作用机制。本研究将为揭示衣原体感染诱导的Gr-1+ MDSC样免疫抑制细胞的作用及作用机制奠定基础，并为衣原体感染的防治提供新的理论依据

流行病学研究显示衣原体感染仍然是严重的世界范围内的公共健康问题，尚无预防衣原体感染的有效疫苗问世。本课题组在前期实验中发现，衣原体感染伴随感染部位Gr-1+细胞大量浸润。为了进一步分析Gr-1+细胞及其亚群构成，明确该细胞在宿主抗衣原体感染中作用及其可能的作用机制，我们完成了以下研究：1. 观察Gr-1+细胞及其亚群在衣原体呼吸道感染进程中的动态变化，发现衣原体感染后肺部浸润Gr-1+细胞逐渐增加，其中CD11b+Ly6ChiLy6G-和 CD11b+Ly6Cint/-Ly6G+亚群为主要的两个亚群。比较衣原体易感鼠C3H/HeN与抵抗鼠C57中Gr-1+细胞及其亚群在百分比构成上的差异，发现C3H鼠中Gr-1+细胞及其亚群的百分比均明显高于C57鼠。提示Gr-1+细胞浸润与疾病的严重程度有关。2. 阐明Gr-1+细胞在宿主抵抗衣原体感染中的作用及机制。采用两种抗体删除Gr-1+细胞，RB6-8C5抗体封闭小鼠肺脏衣原体负荷显著高于对照组，肺部病变更重。脾脏及肺脏中CD8+T细胞百分比明显下降，CD4+T细胞和CD8+T细胞产生IFNγ显著低于对照组，而 CD4+T细胞产生IL－4高于对照组。结果说明RB6-8C5抗体封闭可能通过减弱保护性的Th1型应答导致感染加重。1A8抗体封闭鼠肺脏衣原体负荷于对照组无明显差异，对T细胞应答影响不显著但肺部病变程度加重。3. 由于封闭实验与我们的预期结果有差距，为了进一步明确Gr-1+细胞中不同亚群在宿主抗衣原体感染中的作用，我们进行了细胞过继转移实验，初步结果提示CD11b+Ly6ChiLy6G-和 CD11b+Ly6Cint/-Ly6G+两种亚群的作用可能是不同的，该部分结果尚需进一步验证。综上所述，本研究为揭示衣原体感染诱导的Gr-1+ MDSC样免疫抑制细胞的作用及作用机制奠定基础。