Role Of CGAS And RIG-? In Innate Immune Response To Chlamydia Trachomatis Infection

Chlamydia trachomatis is Gram-negative,obligate intracellular bacterium that causes eye infection and urogenital track infection.C.trachomatis infection is among the most commonly reported sexually transmitted disease(STD),causing urethritis in men,and pelvic inflammatory disease(PID),tubal blockage and ectopic pregnancy and infertility in women.The pathogenesis of C.trachomatis infection lies in the immune injury resulted from the directly effects of bacteria and immune response after pathogens infection.However,the mechanisms of immune recognition and response to C.trachomatis infection still remains incomplete.Additionally,patients infected with C.trachomatis are often with few or no clinical symptoms(asymptomatic)that make diagnosis and detection even harder.This indicates the infection is elusive which might due to the immune evasion strategies the bacterium employs.Therefore,investigate host immune response and escaping strategy employed by Chlamydia might help to defense and treatment against C.trachomatis infection.Chapter 1 reviews the latest research progress of mechanisms involved in immune recognition of C.trachomatis and sumarizes the function of cGAS,a new cytoplasmic recognition receptor,in the process of microbial infections.In the chapter 2,we explored the C.trachomatis immune recognition mechanism of activate type ? IFN response in HeLa 229 cells.This study suggested that in the early stage of C.trachomatis infection,it activates the type ? IFN pathway accompanied with induced expression of RNA recognition receptor RIG-I.During the infection,the activation of interferon pathway is earlier than CT012 expression and c-di-AMP production.Further studies showed that transient transfection using purified DNA or RNA isolated from C.trachomatis resulted in up-regulation of IFNP and ISG56 genes.We therefore focused on RIG-1 and cyclic-GMP-AMP(cGAMP)synthase(cGAS)since those PRRs play a significant role in host recognition of invading viruses and bacteria.In present study,we demonstrated the production of cGAMP in C.trachomatis infected samples via LC-MS detection.The production of cGAMP is concomitant with the type ? IFN response,suggesting that the C.trachomatis infection might be correlated with nucleic acid secretion.In chapter 3,We investigated the interference in the infection of C.trachomatis in the cGAS/STING pathway.In the research,we observed the cleave of the host cytoplasmic DNA recognition receptor cGAS during the infection of C.trachomatis.We proved this cleavage activity is derived from the C.trachomatis while not the host cell.Though immunodepletion and in vitro enzymatic reaction experiment,our previous work revealed that CPAF,a protease encoded by CT858 gene of C.trachomatis could specific cleave cGAS protein.Further investigation proved the C.trachomatis CPAF protease fulfilled the cleavage of cGAS.This results indicated that the cleavage of cGAS by C.trachomatis may be related to immune escape.In this dissertation,we discussed the immune recognition and immunologic escape mechanisms during the infection process of C.trachomatis.It was revealed that the activation of type ? IFN pathway relays on the host cytoplasmic RNA and DNA recognition receptor RIG-I and cGAS,and proved that the C.trachomatis CPAF protease fulfilled the cleavage of cGAS.In addition,the cleavage of cGAS lead to lost ability to synthesize cGAMP.Herein,our work will provide a new insight in studying host immune recognition and evasion mechanisms during the bacterial infection.