Hongyu Qiu

Type I IFNs Enhance Susceptibility to Chlamydia muridarum Lung Infection by Enhancing Apoptosis of Local Macrophages

Type I IFNs (IFNIs) have pleiotropic functions in regulating host innate and adaptive immune responses to pathogens. To elucidate the role of IFNIs in host resistance to chlamydial infection in vivo, we compared IFN-α/β receptor knockout (IFNAR−/−) and wild-type control mice in susceptibility to Chlamydia trachomatis mouse pneumonitis (Chlamydia muridarum) lung infection. We found that the IFNAR−/− mice were significantly more resistant to C. muridarum infection showing less bacterial burden and bodyweight loss, and milder pathological changes. However, IFN-γ response, which is believed to be critical in host defense against chlamydial infection, was similar between the wild-type and IFNAR−/− mice. More importantly, TUNEL analysis showed less macrophage apoptosis in IFNAR−/− mice, which was consistent with lower expressions of IFNI-induced apoptotic factors, TRAIL, Daxx, and PKR. Furthermore, depletion of lung macrophages with dichloromethylene diphosphonate-liposome significantly increased the susceptibility of the IFNAR−/− mice to C. muridarum, confirming the importance of macrophages. Overall, the data indicate that IFNIs play a promoting role in C. muridarum lung infection, largely through increase of local macrophage apoptosis.

Distinct NKT Cell Subsets Are Induced by Different Chlamydia Species Leading to Differential Adaptive Immunity and Host Resistance to the Infections

We investigated the role of NKT cells in immunity to Chlamydia pneumoniae and Chlamydia muridarum infections using a combination of knockout mice and specific cellular activation approaches. The NKT-deficient mice showed exacerbated susceptibility to C. pneumoniae infection, but more resistance to C. muridarum infection. Activation of NKT reduced C. pneumoniae in vivo growth, but enhanced C. muridarum infection. Cellular analysis of invariant NKT cells revealed distinct cytokine patterns following C. pneumoniae and C. muridarum infections, i.e., predominant IFN-γ in the former, while predominant IL-4 in the latter. The cytokine patterns of CD4+ and CD8+ T cells matched those of NKT cells. Our data provide in vivo evidence for a functionally diverse role of NKT cells in immune response to two intracellular bacterial pathogens. These results suggest that distinct NKT subsets are induced by even biologically closely related pathogens, thus leading to differential adaptive immune response and infection outcomes.

Natural Killer T Cells Are Critical for Dendritic Cells to Induce Immunity in Chlamydial Pneumonia

RATIONALE We previously showed an important role of natural killer T cells (NKT) in skewing the adaptive T cell immunity to Chlamydia pneumoniae (Cpn), an intracellular bacterial lung infection, but the mechanism remains unclear. OBJECTIVES To investigate the underlying mechanism by which NKT modulate T cell responses in chlamydial pneumonia. METHODS We examined the effect of NKT activation in modulating DC function, especially in generating protective immunity against Cpn infection using combination of NKT knockout (KO) mice and specific NKT activation approaches. MEASUREMENTS AND MAIN RESULTS We found that NKT activation in vivo after Cpn infection induces phenotypic and functional changes in dendritic cells (DC). DC from NKT-deficient mice showed reduced CD40 expression and IL-12 production, whereas enhancing NKT activation using alpha-GalCer increased CD40 expression and IL-12 production. Co-culture of DC with NKT enhanced bioactive IL-12p70 production by DC in a CD40L-, IFN-gamma-, and cell-cell contact-dependent manner. Further, co-culture of T cells with DC isolated from infected wild-type (WT) and NKT-deficient mice induced type-1 and type-2 responses, respectively, while DC from alpha-GalCer-treated, infected mice led to enhanced type-1 responses. Moreover, upon adoptive transfer, DC from infected WT mice induced strong type-1 immunity, whereas those from knockout mice induced type-2 responses and increased disease severity upon challenge infection. CONCLUSIONS Our results provide direct evidence of the critical role of NKT activation in the functional modulation of DC for the development of protective immunity in a clinically relevant respiratory infection.

Dendritic cells from Chlamydia‐infected mice show altered Toll‐like receptor expression and play a crucial role in inhibition of allergic responses to ovalbumin

Our previous study has shown that Chlamydia lung infection can inhibit local eosinophilic inflammation induced by allergen sensitization and challenge, which is correlated with altered cytokine production. In the present study, we examined the role played by dendritic cells (DC) in chlamydial infection‐mediated modulation of allergic responses. The results showed that DC freshlyisolated from Chlamydia‐infected mice (iIDC), unlike those from naive control mice (iNDC), could efficiently modulate immune responses to ovalbumin in vitro and in vivo. Co‐culture of freshly isolated DC with naive CD4 cells from T cell receptor transgenic mice (DO11.10) showed that iIDC directed Th1‐dominant, while iNDC directed Th2‐dominant, allergen‐specific CD4 T cell responses. Moreover, adoptive transfer of iIDC, but not iNDC, could inhibit systemic and local eosinophilia induced by allergen exposure. The reduction of eosinophilia was associated with a decrease in IL‐5 receptor expression on bone marrow cells and the production of IL‐5 and IL‐13 by T lymphocytes. Analysis of the DC showed that iIDC expressed significantly higher levels of mRNA for Toll‐like receptor 9 and produced more IL‐12 compared to iNDC. The data demonstrate a critical role played by DC in infection‐mediated inhibition of allergic responses.

NK Cells Promote Type 1 T Cell Immunity through Modulating the Function of Dendritic Cells during Intracellular Bacterial Infection

Dendritic cells (DC) play a key role in establishing protective adaptive immunity in intracellular bacterial infections, but the cells influencing DC function in vivo remain unclear. In this study, we investigated the role of NK cells in modulating the function of DC using a murine Chlamydia infection model. We found that the NK cell-depleted mice showed exacerbated disease after respiratory tract Chlamydia muridarum infection, which was correlated with altered T cell cytokine profile. Furthermore, DC from C. muridarum-infected NK-depleted mice (NK−DC) exhibited a less mature phenotype compared with that of DC from the infected mice without NK depletion (NK+DC). NK−DC produced significantly lower levels of both IL-12 and IL-10 than those of NK+DC. Moreover, NK−DC showed reduced ability to direct primary and established Ag-specific Th1 CD4+ T cell responses in DC–T coculture systems. More importantly, adoptive transfer of NK−DC, in contrast to NK+DC, failed to induce type 1 protective immunity in recipients after challenge infection. Finally, NK cells showed strong direct enhancing effect on IL-12 production by DC in an NK–DC coculture system, which was partially reduced by blocking NKG2D receptors signaling and virtually abolished by neutralizing IFN-γ activity. The data demonstrate a critical role of NK cells in modulating DC function in an intracellular bacterial infection.

Dendritic Cells from Mycobacteria-Infected Mice Inhibits Established Allergic Airway Inflammatory Responses to Ragweed via IL-10– and IL-12–Secreting Mechanisms

Previous studies have demonstrated that Mycobacterium bovis bacillus Calmette-Guerin (BCG) infection can inhibit de novo and established allergen-induced asthma-like responses. The aim of this study was to examine the role of dendritic cells (DCs) in BCG infection-mediated inhibition of established allergy to a common environmental allergen—ragweed. The results showed that adoptive transfer of DCs from BCG-infected mice (DC[BCG]), in contrast to DCs from naive mice (DC[naive]), significantly inhibited established allergic airway eosinophilia and mucus overproduction. The inhibitory effect was correlated with alterations of allergen-driven cytokine and chemokine production as well as VCAM-1 expression in the lung. Flow cytometric analysis showed higher surface expression of CD8α and costimulatory markers in DC(BCG) than in DC(naive). Moreover, DC(BCG) produced significantly higher levels of IL-10 and IL-12 and expressed higher levels of TLRs than did DC(naive). Furthermore, blockade of IL-10 or IL-12 significantly reversed the inhibitory effect of DC(BCG) on established allergic airway inflammation and Th2 cytokine responses. These findings suggest that DCs play a crucial role in infection-mediated inhibition of established allergic responses, and IL-10 and IL-12 production by these DCs may be a major mechanism for the inhibition.

Chlamydia infection induces ICOS ligand-expressing and IL-10-producing dendritic cells that can inhibit airway inflammation and mucus overproduction elicited by allergen challenge in BALB/c mice.

Our previous study has shown that the adoptive transfer of dendritic cells (DCs) freshly isolated from Chlamydia-infected mice (iIDCs), unlike those from control naive mice (iNDCs), can inhibit systemic and cutaneous eosinophilia induced by OVA exposure. In the present study, we examined the mechanism by which iIDC inhibits allergen-specific Th2 cell differentiation in vitro and in vivo. The study revealed that iIDCs exhibited higher surface expression of CD8α and the ICOS ligand (ICOS-L), as well as higher IL-10 and IL-12 production than iNDCs. In vitro DC:CD4+ T cell coculture experiments showed that iIDCs could inhibit allergen-specific Th2 cell differentiation and that the inhibitory effect could be abolished by the blockage of IL-10 or IL-12 activity. More interestingly, the coblockade of IL-10 and the ICOS-L showed synergistic effect in enhancing allergen-driven Th2 cytokine production. Furthermore, adoptive transfer of iIDCs, but not iNDCs, to OVA sensitized mice significantly inhibited airway eosinophilia and mucus overproduction following intranasal challenge with OVA. Overall, the data demonstrate a critical role played by ICOS-L-expressing and IL-10-producing DCs from Chlamydia-infected mice in the infection-mediated inhibition of allergic responses.

Intranasal inoculation of Chlamydia trachomatis mouse pneumonitis agent induces significant neutrophil infiltration which is not efficient in controlling the infection in mice

Previous studies have shown that chlamydial infection is accompanied by significant infiltration of neutrophils at the site of infection. However, the role of neutrophils in host defence against chlamydial infection is not clearly understood. Using genetically different inbred mouse strains and CXCR‐2 gene knockout (KO) mice, we examined the mechanism for neutrophil recruitment and the role of neutrophils during chlamydial lung infection. Our data showed that C3H mice exhibited significantly higher and more persistent neutrophil infiltration in the lung than did C57BL/6 mice following Chlamydia trachomatis mouse pneumonitis infection. The massive neutrophil infiltration in C3H mice was paralleled by high‐level expression of CXCR‐2 and its ligands, CXC chemokines (macrophage inflammatory protein 2, cytokine‐induced neutrophil attractant (KC) and lipopolysaccharide‐induced CXC chemokine), and proinflammatory cytokines (tumour necrosis factor‐α, interleukin‐1 and interleukin‐6) in the lung. Although much greater infiltration of neutrophils was observed in C3H mice than in C57BL/6 mice, the former mice had more severe disease and higher in vivo chlamydial growth than the latter. Moreover, CXCR‐2 KO mice, which revealed a dramatic reduction in neutrophil activity, showed comparable chlamydial infection to wild‐type mice. These results suggest that neutrophils are not efficient for controlling chlamydial lung infection.

Less inhibition of interferon‐γ to organism growth in host cells may contribute to the high susceptibility of C3H mice to Chlamydia trachomatis lung infection

T‐helper‐1‐like cytokine response and cell‐mediated immunity have been shown to be critical in host resistance to Chlamydia trachomatis infection. Using a murine pneumonia model, we compared the susceptibility of C3H/HeN (C3H) and C57BL/6 mice to C. trachomatis mouse pneumonitis (MoPn) infection. C3H mice exhibited significantly higher mortality, greater organism growth and much more severe pathological changes in the lung compared with C57BL/6 mice. However, the pattern of adaptive immune responses including organism‐specific delayed‐type hypersensitivity, antibody responses and cytokine [interferon‐γ (IFN‐γ), interleukin‐12 (IL‐12), IL‐4, IL‐10 and tumour necrosis factor α] production by spleen and local draining lymph node cells in these two strains of mice appeared comparable during the process of infection. Interestingly, MoPn growth in the cultured ex vivo macrophages from C3H mice was found to be significantly less inhibited by the exogenous IFN‐γ present in the culture compared to C57BL/6 mice. The lower inhibition of MoPn growth in C3H mice was associated with significantly lower nitric oxide production by the infected macrophages following IFN‐γ stimulation. The data suggest that the cellular events downstream of cytokine production in chlamydia host cells may be important in determining the different susceptibility of hosts to chlamydial infection.

NK Cells Contribute to Intracellular Bacterial Infection-Mediated Inhibition of Allergic Responses

To experimentally examine the hygiene hypothesis, here we studied the effect of chlamydial infection on the development of allergic responses induced by OVA and the involvement of NK cells in this process using a mouse model of airway inflammation. We found that prior Chlamydia muridarum infection can inhibit airway eosinophilic inflammation and mucus production induced by allergen sensitization and challenge. The inhibition was correlated with an alteration of allergen-driven cytokine-producing patterns of T cells. We demonstrated that NK cells were activated following chlamydial infection, showing both cell expansion and cytokine secretion. The in vivo depletion of NK cells using anti-NK Ab before OVA sensitization and challenge partially abolished the inhibitory effect of chlamydial infection, which was associated with a partial restoration of Th2 cytokine production. In contrast, the adoptive transfer of NK cells that were isolated from infected mice showed a significant inhibitory effect on allergic responses, similar to that observed in natural infection. The data suggest that the innate immune cells such as NK cells may play an important role in infection-mediated inhibition of allergic responses.