百日咳毒素（PT）是百日咳鲍特菌最为重要的毒力因子，具有抑制固有免疫和适应性免疫的作用，但其诱导这些抑制效应的具体机制尚不明确。我们前期发现，PT注射后小鼠的外周血与脾脏中髓样抑制性细胞（MDSCs）显著增加，体外实验PT也明显地促进MDSCs增多，而MDSCs是新近发现的免疫负调控的关键因素。据此推测MDSCs聚积可能是PT引起系列免疫抑制效应的重要环节。本项目拟通过临床病例检测明确百日咳患儿外周血中MDSCs的数量、表型及亚群组成；采用MDSCs过继转移和清除等动物实验，阐明PT诱导的MDSCs对固有免疫细胞分化、抗体产生、T细胞亚群增殖分化等的影响；在体外细胞培养的基础上，采用RNA-Sequencing及CRISPR/Cas9敲除技术等方法，明确PT引起MDSCs聚积的分子机制。研究结果可提高对PT免疫学作用和机制的认识，可为百日咳发病机制和干预研究提供新的思路。

Pertussis toxin (PT) is one of the most important virulence factors of B. pertussis, and it has a remarkable ability to inhibit innate and adaptive immunity. However, the mechanism is still not very clear. Our recent studies have found that PT treatment in vivo promoted the accumulation of myeloid-derived suppressor cells (MDSCs) in the blood and spleen of mouse, PT treatment in vitro also induced MDSC accumulation, While, MDSCs are regarded as important negative immune regulators in recent years. We speculated that MDSC accumulation is the key point of PT-induced immune suppression. We will collect the blood of pertussis patients and analysis the number and phenotype of MDSCs. The immune effect of MDSCs on innate immune cell differentiation, antibody production and T cell responses will be tested by MDSC adoptive transfer and depletion in vivo. The molecular mechanisms of PT induced MDSC accumulation will be investigated in cell experiments through RNA-Sequencing and CRISPR/Cas9. The result is not only helpful for identifying immune and pathogenic mechanism of PT, but also providing new ideas for pertussis diagnosis and intervention.