The Role Of PGRN In Chlamydia Pulmonary Infection Of Mice

Background:Chlamydia is an obligate intracellular parasitic pathogen and Gram-negative prokaryotic microorganism,including the well-known human pathogens Chlamydiatrachomatis(C.trachomatis)and Chlamydia pneumoniae(C.pneumoniae).Chlamydia infects the conjunctiva,respiratory and genital mucosal epithelial cells,which lead to a variety of human diseases.After infection,Chlamydia replicates within the inclusion body and escapes from the host immunosurveillance,which frequently results in persistent infectionand prolonged course of diseases with irreversible pathological lesions or even serious complications.Chlamydia trachomatis infection of the respiratory tractcan induce host immune response,in which both innate and adaptive immunity play important anti-infection effects.Chlamydia infection activates innate immune cells,including dendritic cells(DCs)and macrophages(MΦs),which are specialized antigen-presenting cells(APCs).As a bridge between innate immunity and adaptive immunity,dendritic cells initiate and direct T cell responses,in which Thl-dominated immune response and Thl cells-produced IFN-γ have been well documented as the major protective factors in the resolution of chlamydial infection.Progranulin(PGRN)is a multifunctional secretory growth factor that plays an important role in both tissue repair and host defense.PGRN is highly expressed in rapidly proliferating epithelial cells,macrophages,dendritic cells,and neurons.Many studies have confirmed that PGRN plays a key role in inflammatory diseases and autoimmune diseases.However,the role of PGRN in infectious diseases is rarely reported and not wellexhaustivestudied.Purpose:In this study,aChlamydia lung infection mouse model was used to investigate the role of PGRN-mediated immunoregulation in intracellular bacterial infection and the effect of PGRN on the cellular immune response in Chlamydia-infected mice in order to provide new potential control strategies for the clinical treatment for Chlamydia infection.Methods:To establish the mouse model of pulmonary chlamydial infection,C57BL/6 mice were intranasally inoculated with C.muridarum(Cm).Then the levels of PGRN in lung tissue and serum were detected,and the expression profile of PGRN in vivo was confirmed by using mouse lung epithelial cells TC-1 in vitro.The bodyweight measurement and lung tissue H&E staining were used to compare the physiological and pathological changes of PGRN knockout(KO)mice and WT mice after infection.Chlamydial loads(IFUs)in the lung was also detected.The immune responses of lung,spleen and lymph nodes were detected by flow cytometry.The levels of cytokines were detected by ELISA.WT or PGRN KO Spleen DCs were isolated from Cm-infected mice.Flow cytometry and ELISA were carried out to detect the levels of activation-associated surface markers and IL-12 production of DCs.WT or KO DCs were cocultured with CD4+ T cells isolated from infected WT mice,and T cells proliferation and IFN-yproductionwere examined.The CCR7 levels of DCs in lung and lymph nodes from WT or KO mice after infection were analyzed by flow cytometry.Results:In the mouse model of pulmonary chlamydial infection,the levels of PGRN in lung tissues and serum of mice were significantly increased.In vitro,theprotein levels and transcriptional levels of PGRN in Cm-infected TC-1 cells were also increased.PGRN deficiency led to accelerated recovery of body weight and decreased chlamydial loads(IFUs)in the lung of Cm-infected mice.H&E staining indicated an ameliorated lung damage in KO mice compared with WT mice at 14 days post Chlamydia infection.After Cm infection,the percentage of IFN-γ-producing CD4+and CD8+ T cells was increased in lung,spleen and lymph nodes of KO mice compared with WT mice.The levels of IFN-y in lung tissue from KO mice were enhanced compared with WT mice at 14 days post Chlamydia infection.The Cm-stimulated production of IL-12p40 and IL-12p70 was increased by DCs isolated from KO mice compared with WT DCs.In the coculture of WT or KO DCs with WT CD4+ T cells,KO DCs were more effectively contribute to the production of IFN-γ and proliferation of T cells.In addition,the percentage of CCR7+DCs was signifincantly enhanced in lung from KO mice compared with WT mice.Conclusion:(1)The levels of PGRN were locally and systemically increased in lung and peripheral blood in the mouse model of Chlamydial pulmonary infection,suggesting that PGRN may be involved in the progression of Chlamydia infection-associated diseases.(2)PGRN deficiency protected mice against Chlamydia infection-induced lung damage,and enhanced host ability of Chlamydia clearance,by which accelerated the improvement of disease.(3)PGRN deficiency boosted the Thl immune response in mice with Chlamydia infection.(4)The maturation and activation of PGRN-deficient DCs were enhanced after Chlamydia challenge,and in turn mediatedmore powerful Thl immune responses compared WT DCs.Therefore,PGRN deficiency may facilitate the activation of DCs,and thus contributes to the clearance of Chlamydia by enhancing Thl immune responses.As an important regulator of immune responses,PGRN plays a crucial role in the pathogenesis of Chlamydia infection,suggesting that PGRN may be a potentialtherapeutic target for Chlamydia infection.