Mechanisms Of Apoptosis Inhibition In Chlamydia Psittaci-Infected Human Neutrophils

Chlamydia psittaci(C.psittaci)is a zoonotic pathogen that causes respiratory in human.Human polymorphonuclear neutrophil(hPMN)is known as the first immune defense of C.psittaci.However,the immune interactions between C.psittaci and hPMN remains unclear.It has been reported that some zoonotic pathogens are capable of not only inhibiting the apoptosis of hPMN,but also self-multiplying in hPMN.Here we studied the molecular mechanism by which C.psittaci interacts with hPMN,as an effort to provide a new insight into the disease-causing mechanism of C.psittaci.Firstly,we cultured C.psittaci in vitro and infected hPMN with different multiplicity of infection(MOI)of C.psittaci.After infection,indirect immunofluorescence,flow cytometry and Western blot were used to study the proliferation of C.psittaci as well as the apoptosis of hPMN.We revealed that C.psittaci can survive and proliferate inside hPMN,and significantly inhibit the apoptosis of hPMN at an MOI of 1:1.Secondly,we studied the effects of C.psittaci infection on the enzymatic activity of caspase-3/7,mitochondrial membrane potential and mitochondrial ATP production via indirect immunofluorescence and enzymatic experiments.The results suggest that C.psittaci can induce hPMN to release ATP,and ATP subsequently activated the P2X7 receptor thereby inhibiting hPMN apoptosis.Thirdly,we observed via indirect immunofluorescence that CPSIT＿0556,a virulence factor of C.psittaci,was located in the inclusion membrane of He La cells.Meanwhile,Western blot and flow cytometry indicates that co-incubation hPMN with CPSIT＿0556 can up-regulate the PI3K/AKT and NF-κB signaling pathway,and as a result,inhibit the apoptosis of hPMN.Last but not the least,ELISA experiments revealed that both C.psittaci and CPSIT＿0556 can induce the IL-8 secretion from hPMN in a time-and dose-dependent manner,and inhibit the apoptosis of hPMN.However,the recombinant human human IL-8 had no effect on the apoptosis of hPMN.In conclusion,this study showed for the first time that C.psittaci can proliferate in hPMN,and inhibite the apoptosis of hPMN by two potential ways: 1)C.psittaci induces hPMN to release ATP,and ATP subsequently activated the P2X7 receptor thereby inhibiting hPMN apoptosis;2)The CPSIT＿0556 inhibits hPMN apoptosis via up-regulating the PI3K/AKT and NF-κB signaling pathways.