The Important Role of Dendritic Cell (DC) in iNKT-Mediated Modulation of NK Cell Function in Chlamydia pneumoniae Lung Infection.

Chlamydia pneumoniae (Cpn) infection causes multiple acute and chronic human diseases. The role of DCs in host defense against Cpn infection has been well documented. The same is true for invariant natural killer T (iNKT) cells and NK cells, but the interaction among cells is largely unknown. In this study, we investigated the influence and mechanism of iNKT cell on the differentiation and function of NK cell in Cpn lung infection and the role played by DCs in this process. We found that expansion of IFN-γ-producing NK cells quickly happened after the infection, but this response was altered in iNKT knockout (KO) mice. The expression of activation markers and the production of IFN-γ by different NK subsets were significantly lower in KO mice than wild-type (WT) mice. Using in vitro DC-NK coculture and in vivo adoptive transfer approaches, we further examined the role of DCs in iNKT-mediated modulation of NK cell function. We found that NK cells expressed lower levels of activation markers and produced less IFN-γ when they were cocultured with DCs from KO mice than WT mice. More importantly, we found that the adoptive transfer of DCs from the KO mice induced less NK cell activation and IFN-γ production. The results provided evidence on the modulating effect of iNKT cell on NK cell function, particularly the critical role of DCs in this modulation process. The finding suggests the complexity of cellular interactions in Cpn lung infection, which should be considered in designing preventive and therapeutic approaches for diseases and infections.

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.

Development and Clinical Performance of InteliSwab® COVID-19 Rapid Test: Evaluation of Antigen Test for the Diagnosis of SARS-CoV-2 and Analytical Sensitivity to Detect Variants of Concern Including Omicron and Subvariants.

BACKGROUND AND OBJECTIVES: Timely detection of SARS-CoV-2 infection with subsequent contact tracing and rapid isolation are considered critical to containing the pandemic, which continues with the emergence of new variants. Hence, there is an ongoing need for reliable point-of-care antigen rapid diagnostic tests (Ag-RDT). This report describes the development, evaluation, and analytical sensitivity of the diagnostic performance of the InteliSwab® COVID-19 Rapid Test. Methods: Samples from 165 symptomatic subjects were tested with InteliSwab® and the results were compared to RT-PCR to determine the antigen test performance. The analytical sensitivity of InteliSwab® for the detection of different variants was assessed by limit of detection (LOD) determination using recombinant nucleocapsid proteins (NPs) and testing with virus isolates. Western immunoblot independently confirmed that each monoclonal Ab is capable of binding to all variants tested thus far. RESULTS: The overall positivity rate by RT-PCR was 37% for the 165 symptomatic subjects. Based on RT-PCR results as the reference standard, InteliSwab® showed clinical sensitivity and specificity of 85.2% (95% CI, 74.3-92.0%) and 98.1% (95% CI, 93.3-99.7%), respectively. The overall agreement was 93.3% (Kappa index value 0.85; 95% CI, 0.77-0.74) between RT-PCR and InteliSwab® test results. Furthermore, the evaluation of analytical sensitivity for different SARS-CoV-2 variants by InteliSwab® was comparable in the detection of all the variants tested, including Omicron subvariants, BA.4, BA.5, and BQ.1. CONCLUSIONS: Due to the surge of infections caused by different variants from time to time, there is a critical need to evaluate the sensitivity of rapid antigen-detecting tests for new variants. The study findings showed the robust diagnostic performance of InteliSwab® and analytical sensitivity in detecting different SARS-CoV-2 variants, including the Omicron subvariants. With the integrated swab and excellent sensitivity and variant detection, this test has high potential as a point-of-care Ag-RDT in various settings when molecular assays are in limited supply and rapid diagnosis of SARS-CoV-2 is necessary.

Invariant NKT cells preferentially modulate the function of CD8 alpha+ dendritic cell subset in inducing type 1 immunity against infection.

Although studies suggest that NKT cell (NKT) activation modulates the function of dendritic cells (DCs) in inducing T cell responses, it is unknown whether this modulating effect is biased to a DC subset. We previously reported that NKT activation could modulate DC function in inducing protective T cell immunity to Chlamydia pneumoniae, an intracellular bacterial infection. In this study, we investigated the effect of NKT activation on DC subsets, using multiple approaches, including gene knockout mice, alpha- galactosylceramide stimulation, adoptive transfer of invariant NKT (iNKT), and functional analysis of DC subsets in both in vitro and in vivo settings. We found a preferential modulating effect of iNKTs on the CD8alpha(+) DC subset. Specifically, we found that iNKT-deficient mice, compared with wild-type (WT) mice, showed reduced CD8alpha(+) DC expansion with lower CD40 expression and IL-12 production, whereas enhancing iNKT activation in WT mice or adoptive transfer of iNKTs to Jalpha18(-/-) mice resulted in increased function of CD8alpha(+) DCs in inducing type 1 immune responses. Further, DC-iNKT coculture experiments showed a direct CD40L-dependent enhancing effect of iNKTs on IL-12p70 production by CD8alpha(+) DCs. More importantly, CD8alpha(+) DCs from Jalpha18(-/-) mice, compared with those from WT mice, showed significantly reduced ability to activate IFN-gamma-producing T cells in vitro and to induce type 1 immunity and protection in vivo. Moreover, a similar CD8alpha(+) DC subset alteration was found in the Jalpha18(-/-) mice following Leishmania major infection. Our data provide the first direct evidence that iNKTs preferentially promote the functional development of a subset of DC to generate protective immunity against infections.

Th1 cytokine responses fail to effectively control Chlamydia lung infection in ICOS ligand knockout mice.

ICOS ligand (ICOSL) plays an important role in controlling specific aspects of T cell activation, differentiation, and function. Th1-type immune responses have been shown to be critical in host defense against chlamydial infections. To assess the role of ICOSL-ICOS interaction in host defense against chlamydial infection, we compared the immune responses and pathological reactions in ICOSL gene knockout (KO) and wild-type (WT) mice following Chlamydia muridarum lung infection. The results showed that ICOSL KO mice exhibited greater body weight loss, higher pathogen burden, and more severe histopathology in their lung than did WT mice. Cytokine analysis revealed that ICOSL KO mice produced lower levels of Th2 (IL-4 and IL-5) and anti-inflammatory (TGF-beta1 and IL-10) cytokines, but higher Th1-related (IFN-gamma and IL-12p40/IL-23) and proinflammatory (IL-6 and TNF-alpha) cytokines. ICOSL KO mice also showed reduced Chlamydia-specific Ab levels in their sera and lung homogenates. In addition, ICOSL KO mice demonstrated significantly lower ICOS expression in T cells and lower Th17 responses than did WT mice. Finally, we showed that ICOS-ICOSL interaction and cell-cell contact are essential for CD4(+) T cells to inhibit chlamydial growth in the cultured lung fibroblasts. The data suggest that ICOSL plays a significant role in immunoregulation and protective immunity against Chlamydia infections and that the Th1 skew in cytokine responses per se is not sufficient for effective control of Chlamydia infections.

IL-17/Th17 promotes type 1 T cell immunity against pulmonary intracellular bacterial infection through modulating dendritic cell function.

Although their contribution to host defense against extracellular infections has been well defined, IL-17 and Th17 are generally thought to have limited impact on intracellular infections. In this study, we investigated the role and mechanisms of IL-17/Th17 in host defense against Chlamydia muridarum, an obligate intracellular bacterium, lung infection. Our data showed rapid increase in IL-17 production and expansion of Th17 cells following C. muridarum infection and significant detrimental impact of in vivo IL-17 neutralization by anti-IL-17 mAb on disease course, immune response, and dendritic cell (DC) function. Specifically, IL-17-neutralized mice exhibited significantly greater body weight loss, higher organism growth, and much more severe pathological changes in the lung compared with sham-treated control mice. Immunological analysis showed that IL-17 neutralization significantly reduced Chlamydia-specific Th1 responses, but increased Th2 responses. Interestingly, the DC isolated from IL-17-neutralized mice showed lower CD40 and MHC II expression and IL-12 production, but higher IL-10 production compared with those from sham-treated mice. In two DC-T cell coculture systems, DC isolated from IL-17-neutralized mice induced higher IL-4, but lower IFN-gamma production by Ag-specific T cells than those from sham-treated mice in cell priming and reaction settings. Adoptive transfer of DC isolated from IL-17-neutralized mice, unlike those from sham-treated mice, failed to protect the recipients against challenge infection. These findings provide in vivo evidence that IL-17/Th17 plays an important role in host defense against intracellular bacterial infection, and suggest that IL-17/Th17 can promote type 1 T cell immunity through modulating DC function.

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-alpha/beta 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-gamma 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.

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.

Role of L-carnitine in the modulation of immune response in aged rats.

BACKGROUND: The immune system undergoes alterations in functions with aging which results in progressive deterioration in the ability to respond to infection. The importance of nutrients in regulating immune responses has widened attempts on interventions that improve immune functions with aging. L-carnitine serves as a vital factor in the mitochondrial transport of fatty acids, a process essential for fatty acid oxidation and energy release. L-carnitine is categorized as a conditionally essential nutrient factor and its concentrations are reported to be decreased with aging. METHODS: The immunomodulatory role of L-carnitine was assessed in aged rats after administration of L-carnitine (300 mg/kg body weight/day) for 7, 14 and 21 days by evaluating neutrophil functions, delayed-type hypersensitivity (DTH) responses and immunoglobulin concentrations. RESULTS: Aged animals exhibited decreased non-specific immune functions, delayed-type hypersensitivity responses and immunoglobulin concentrations compared to younger controls. Treatment with L-carnitine improved neutrophil functions, delayed-type hypersensitivity responses and the concentrations of immunoglobulins A and G in aged animals in a significant manner. However L-carnitine treatment did not have any impact on IgM concentration and type responses. CONCLUSIONS: This study demonstrated that aging is associated with a decline in immune functions and supplementing L-carnitine had a positive effect in improving immune responses in aged animals.

Respective IL-17A production by γδ T and Th17 cells and its implication in host defense against chlamydial lung infection.

The role of IL-17A is important in protection against lung infection with Chlamydiae, an obligate intracellular bacterial pathogen. In this study, we explored the producers of IL-17A in chlamydial lung infection and specifically tested the role of major IL-17A producers in protective immunity. We found that γδT cells and Th17 cells are the major producers of IL-17A at the early and later stages of chlamydial infection, respectively. Depletion of γδT cells in vivo at the early postinfection (p.i.) stage, when most γδT cells produce IL-17A, failed to alter Th1 responses and bacterial clearance. In contrast, the blockade of IL-17A at the time when IL-17A was mainly produced by Th17 (day 7 p.i.) markedly reduced the Th1 response and increased chlamydial growth. The data suggest that the γδ T cell is the highest producer of IL-17A in the very early stages of infection, but the protection conferred by IL-17A is mainly mediated by Th17 cells. In addition, we found that depletion of γδ T cells reduced IL-1α production by dendritic cells, which was associated with a reduced Th17 response. This finding is helpful to understand the variable role of IL-17A in different infections and to develop preventive and therapeutic approaches against infectious diseases by targeting IL-17A.

Novel Clostridium difficile Anti-Toxin (TcdA and TcdB) Humanized Monoclonal Antibodies Demonstrate In Vitro Neutralization across a Broad Spectrum of Clinical Strains and In Vivo Potency in a Hamster Spore Challenge Model.

Clostridium difficile (C. difficile) infection (CDI) is the main cause of nosocomial antibiotic-associated colitis and increased incidence of community-associated diarrhea in industrialized countries. At present, the primary treatment of CDI is antibiotic administration, which is effective but often associated with recurrence, especially in the elderly. Pathogenic strains produce enterotoxin, toxin A (TcdA), and cytotoxin, toxin B (TcdB), which are necessary for C. difficile induced diarrhea and gut pathological changes. Administration of anti-toxin antibodies provides an alternative approach to treat CDI, and has shown promising results in preclinical and clinical studies. In the current study, several humanized anti-TcdA and anti-TcdB monoclonal antibodies were generated and their protective potency was characterized in a hamster infection model. The humanized anti-TcdA (CANmAbA4) and anti-TcdB (CANmAbB4 and CANmAbB1) antibodies showed broad spectrum in vitro neutralization of toxins from clinical strains and neutralization in a mouse toxin challenge model. Moreover, co-administration of humanized antibodies (CANmAbA4 and CANmAbB4 cocktail) provided a high level of protection in a dose dependent manner (85% versus 57% survival at day 22 for 50 mg/kg and 20 mg/kg doses, respectively) in a hamster gastrointestinal infection (GI) model. This study describes the protective effects conferred by novel neutralizing anti-toxin monoclonal antibodies against C. difficile toxins and their potential as therapeutic agents in treating CDI.

Dynamics of NKT-Cell Responses to Chlamydial Infection.

Natural killer T (NKT) cells have gained great attention owing to their critical functional roles in immunity to various pathogens. In this review, we provide an overview of the current knowledge on the role of NKT cells in host defense against and pathogenesis due to Chlamydia, which is an intracellular bacterial pathogen that poses a threat to the public health worldwide. Accumulating evidence has demonstrated that NKT cells, particularly invariant NKT (iNKT) cells, play a crucial role in host defense against chlamydial infections, especially in C. pneumoniae infection. iNKT cells can promote type-1 protective responses to C. pneumoniae by inducing enhanced production of IL-12 by dendritic cells (DCs), in particular CD8α+ DCs, which promote the differentiation of naive T cells into protective IFN-γ-producing Th1/Tc1 type CD4+/CD8+ T cells. This iNKT-cell-mediated modulation of DC function is largely dependent upon CD40-CD40L interaction, IFN-γ production, and cell-to-cell contact. In addition, iNKT cells modulate the function of natural killer cells. NKT cells may be also involved in the pathogenesis of some chlamydial diseases by inducing different patterns of cytokine production. A better understanding of NKT-cell biology will enable us to rationally design prophylactic and therapeutic tools to combat infectious diseases.

Invariant Natural Killer T Cells Promote T Cell Immunity by Modulating the Function of Lung Dendritic Cells during Chlamydia pneumoniae Infection.

In this study, we examined the effect of invariant natural killer T (iNKT) cells on the function of lung dendritic cells (LDCs) in eliciting protective immunity against Chlamydia pneumoniae (Cpn) lung infection. We employed a combination of approaches including the use of iNKT cell-deficient, Jα18-knockout (KO) mice and LDC adoptive transfer. We found that iNKT cells significantly altered the number, phenotype and cytokine profile of LDCs following infection. Furthermore, coculture of T cells with LDCs from Cpn-infected wild-type (WT) and KO mice induced type-1 and type-2 responses, respectively. More importantly, upon adoptive transfer, LDCs from Cpn-infected WT mice (WT-LDCs) conferred protective immunity, whereas LDCs from KO mice (KO-LDCs) increased the severity of disease after challenge infection. Further cytokine analyses of the lung tissues and lung-draining lymph node cells showed that KO-LDC-recipient mice exhibited a type-2 cytokine production pattern, while WT-LDC recipients exhibited a type-1 cytokine profile. Taken together, our results provide in vivo evidence that iNKT cells play a critical role in modulating LDC function to generate protective T-cell immunity, particularly in a clinically relevant intracellular bacterial infection.

Invariant natural killer T cells: boon or bane in immunity to intracellular bacterial infections?

Invariant natural killer T (iNKT) cells represent a specialized subset of innate lymphocytes that recognize lipid and glycolipid antigens presented to them by nonclassical MHC-I CD1d molecules and are able to rapidly secrete copious amounts of a variety of cytokines. iNKT cells possess the ability to modulate innate as well as adaptive immune responses against various pathogens. Intracellular bacteria are one of the most clinically significant human pathogens that effectively evade the immune system and cause a myriad of diseases of public health concern globally. Emerging evidence suggests that iNKT cells can confer immunity to intracellular bacteria but also inflict pathology in certain cases. We summarize the current knowledge on the contribution of iNKT cells in the host defense against intracellular bacterial infections, with a focus on the underlying mechanisms by which these cells induce protective or pathogenic reactions including the pathways of direct action (acting on infected cells) and indirect action (modulating dendritic, NK and T cells). The rational exploitation of iNKT cells for prophylactic and therapeutic purposes awaits a profound understanding of their functional biology.

Plasmacytoid dendritic cells mediate the regulation of inflammatory type T cell response for optimal immunity against respiratory Chlamydia pneumoniae infection.

Chlamydia pneumoniae (Cpn) infection is a leading cause for a variety of respiratory diseases and has been implicated in the pathogenesis of chronic inflammatory diseases. The regulatory mechanisms in host defense against Cpn infection are less understood. In this study, we investigated the role of plasmacytoid dendritic cells (pDCs) in immune regulation in Cpn respiratory tract infection. We found that in vivo depletion of pDCs increased the severity of infection and lung pathology. Mice depleted of pDC had greater body weight loss, higher lung bacterial burden and excessive tissue inflammation compared to the control mice. Analysis of specific T cell cytokine production pattern in the lung following Cpn infection revealed that pDC depleted mice produced significantly higher amounts of inflammatory cytokines, especially TNF-α, but lower IL-10 compared to the controls. In particular, pDC depleted mice showed pathogenic T cell responses characterized by inflammatory type-1 (CD8 and CD4) and inflammatory Th2 cell responses. Moreover, pDC depletion dramatically reduced CD4 regulatory T cells (Tregs) in the lungs and draining lymph nodes. Furthermore, pDC-T cell co-culture experiments showed that pDCs isolated from Cpn infected mice were potent in inducing IL-10 producing CD4 Tregs. Together, these findings provide in vivo evidence for a critical role of pDCs in homeostatic regulation of immunity during Cpn infection. Our findings highlight the importance of a 'balanced' immune response for host protective immunity and preventing detrimental immunopathology during microbial infections.

Effects of Clostridium difficile toxin A and B on human T lymphocyte migration.

Bacterial products such as toxins can interfere with a variety of cellular processes, leading to severe human diseases. Clostridium difficile toxins, TcdA and TcdB are the primary contributing factors to the pathogenesis of C. difficile-associated diseases (CDAD). While the mechanisms for TcdA and TcdB mediated cellular responses are complex, it has been shown that these toxins can alter chemotactic responses of neutrophils and intestinal epithelial cells leading to innate immune responses and tissue damages. The effects of C. difficile toxins on the migration and trafficking of other leukocyte subsets, such as T lymphocytes, are not clear and may have potential implications for adaptive immunity. We investigated here the direct and indirect effects of TcdA and TcdB on the migration of human blood T cells using conventional cell migration assays and microfluidic devices. It has been found that, although both toxins decrease T cell motility, only TcdA but not TcdB decreases T cell chemotaxis. Similar effects are observed in T cell migration toward the TcdA- or TcdB-treated human epithelial cells. Our study demonstrated the primary role of TcdA (compared to TcdB) in altering T cell migration and chemotaxis, suggesting possible implications for C. difficile toxin mediated adaptive immune responses in CDAD.

L-carnitine mediates protection against DNA damage in lymphocytes of aged rats.

It has been proposed that age-associated disorders are related to a time-dependent shift in the antioxidant/prooxidant balance towards oxidative damage. Increased production of oxidants in vivo can cause damage to intracellular macromolecules such as DNA, proteins and lipids, which can in turn lead to oxidative injury. Carnitine is a vitamin-like compound that serves as a carrier to transport long-chain fatty acids into the mitochondria for beta-oxidation. In the present study, the effect of L-carnitine, a widely recognized essential nutrient, was evaluated on the status of lipid peroxidation and certain antioxidant enzymes and DNA damage in lymphocytes with relation to age in male wistar rats. The levels of lipid peroxides were remarkably increased whereas, the activities of antioxidant enzymes were significantly decreased in aged control animals when compared to younger controls. In aged animals, administration of L-carnitine for 21 days significantly decreased the levels of lipid peroxides and improved the activities of antioxidant enzymes like superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase. L-Carnitine enhanced T-cell proliferative responses as evaluated by T-cell proliferation assay using [3H] thymidine incorporation and also significantly reduced DNA damage, apoptosis and TNF-alpha level in lymphocytes of aged animals. Our results suggest that L -carnitine may have a vital role in improving functions in the cells of the immune system particularly the lymphocytes possibly through its antioxidant action.

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-gamma 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.

Adoptive transfer of CD8alpha+ dendritic cells (DC) isolated from mice infected with Chlamydia muridarum are more potent in inducing protective immunity than CD8alpha- DC.

Chlamydial infections are serious public health concerns worldwide. In this study, we examined the role of dendritic cell (DC) subsets in inducing protective immunity against chlamydial infection using an adoptive transfer approach. We found that CD11c+CD8alpha+ (double-positive, DP) DC, compared with CD11c+CD8alpha- (single-positive, SP) DC isolated from infected mice, are more potent inducers of protective immunity. Specifically, mice pretreated with DPDC from infected mice, upon infection with Chlamydia trachomatis mouse pneumonitis (MoPn), experienced significantly less severe body weight loss and in vivo chlamydial growth. Analysis of MoPn-driven cytokine production by immune cells revealed that mice that were treated with DPDC produced significantly higher levels of Th1 (TNF-alpha, IFN-gamma, and IL-12) but lower levels of Th2 (IL-4, IL-5, and IL-13)-related cytokines than the recipients of SPDC following infection challenge. Moreover, DPDC-treated mice displayed significantly higher levels of MoPn-specific IgG2a production and delayed-type hypersensitivity responses compared with SPDC-treated mice. Furthermore, DPDC isolated from infected mice produced higher amounts of IL-12 and IL-10 in vitro in comparison with SPDC. These data indicate that CD8alpha+ DC have a significantly higher capacity in inducing protective immunity compared with CD8alpha- DC, demonstrating the crucial role of DC1-like cells in eliciting protection against C. trachomatis infection.

NK T cell activation promotes Chlamydia trachomatis infection in vivo.

We used two approaches to examine the role of NK T cells (NKT) in an intracellular bacterial (Chlamydia trachomatis mouse pneumonitis (C. muridarum)) infection. One is to use CD1 gene knockout (KO) mice, which lack NKT, and the other is to activate NKT using alpha-galactosylceramide (alpha-GalCer), a natural ligand of these cells. The data showed a promoting effect of NKT activation on Chlamydia lung infection. Specifically, CD1 KO mice exhibited significantly lower levels of body weight loss, less severe pathological change and lower chlamydial in vivo growth than wild-type mice. Immunological analysis showed that CD1 KO mice exhibited significantly lower C. muridarum-specific IL-4 and serum IgE Ab responses as well as more pronounced delayed-type hypersensitivity response compared with wild-type controls. In line with the finding in KO mice, the in vivo stimulation of NKT using alpha-GalCer enhanced chlamydial growth in vivo, which were correlated with reduced delayed-type hypersensitivity response and increased C. muridarum-driven IL-4/IgE production. Moreover, neutralization of IL-4 activity in the alpha-GalCer-treated BALB/c mice significantly reduced the promoting effect of alpha-GalCer treatment on chlamydial growth in vivo. These data provide in vivo evidence for the involvement of NKT in a bacterial pathogenesis and its role in promoting Th2 responses during infection.