Goro Matsuzaki

IL-17-Mediated Regulation of Innate and Acquired Immune Response against Pulmonary Mycobacterium bovis Bacille Calmette-Guérin Infection

IL-17 is a cytokine that induces neutrophil-mediated inflammation, but its role in protective immunity against intracellular bacterial infection remains unclear. In the present study, we demonstrate that IL-17 is an important cytokine not only in the early neutrophil-mediated inflammatory response, but also in T cell-mediated IFN-γ production and granuloma formation in response to pulmonary infection by Mycobacterium bovis bacille Calmette-Guérin (BCG). IL-17 expression in the BCG-infected lung was detected from the first day after infection and the expression depended on IL-23. Our observations indicated that γδ T cells are a primary source of IL-17. Lung-infiltrating T cells of IL-17-deficient mice produced less IFN-γ in comparison to those from wild-type mice 4 wk after BCG infection. Impaired granuloma formation was also observed in the infected lungs of IL-17-deficient mice, which is consistent with the decreased delayed-type hypersensitivity response of the infected mice against mycobacterial Ag. These data suggest that IL-17 is an important cytokine in the induction of optimal Th1 response and protective immunity against mycobacterial infection.

IL-17A Produced by γδ T Cells Plays a Critical Role in Innate Immunity against Listeria monocytogenes Infection in the Liver

IL-17A is originally identified as a proinflammatory cytokine that induces neutrophils. Although IL-17A production by CD4+ Th17 T cells is well documented, it is not clear whether IL-17A is produced and participates in the innate immune response against infections. In the present report, we demonstrate that IL-17A is expressed in the liver of mice infected with Listeria monocytogenes from an early stage of infection. IL-17A is important in protective immunity at an early stage of listerial infection in the liver because IL-17A-deficient mice showed aggravation of the protective response. The major IL-17A-producing cells at the early stage were TCR γδ T cells expressing TCR Vγ4 or Vγ6. Interestingly, TCR γδ T cells expressing both IFN-γ and IL-17A were hardly detected, indicating that the IL-17A-producing TCR γδ T cells are distinct from IFN-γ-producing γδ T cells, similar to the distinction between Th17 and Th1 in CD4+ T cells. All the results suggest that IL-17A is a newly discovered effector molecule produced by TCR γδ T cells, which is important in innate immunity in the liver.

Essential Role of IL-17A in the Formation of a Mycobacterial Infection-Induced Granuloma in the Lung

Granulomas play an essential role in the sequestration and killing of mycobacteria in the lung; however, the mechanisms of their development and maturation are still not clearly understood. IL-17A is involved in mature granuloma formation in the mycobacteria-infected lung. Therefore, IL-17A gene-knockout (KO) mice fail to develop mature granulomas in the Mycobacterium bovis bacille Calmette-Guérin (BCG)-infected lung. This study analyzed the mechanism of IL-17A–dependent mature granuloma formation in the mycobacteria-infected lung. The IL-17A KO mice showed a normal level of nascent granuloma formation on day 14 but failed to develop mature granulomas on day 28 after the BCG infection in the lung. The observation implies that IL-17A is required for the maturation of granuloma from the nascent to mature stage. TCR γδ T cells expressing TCR Vγ4 or Vγ6 were identified as the major IL-17A–producing cells that resided in the BCG-induced lung granuloma. The adoptive transfer of the IL-17A–producing TCR γδ T cells reconstituted granuloma formation in the IL-17A KO mice. The expression of ICAM-1 and LFA-1, which are adhesion molecules important in granuloma formation, decreased in the lung of the BCG-infected IL-17A KO mice, and their expression was induced on BCG-infected macrophages in coculture with IL-17A–producing TCR γδ T cells. Furthermore, IL-17A KO mice showed not only an impaired mature granuloma formation, but also an impaired protective response to virulent Mycobacterium tuberculosis. Therefore, IL-17A produced by TCR γδ T cells plays a critical role in the prevention of M. tuberculosis infection through the induction of mature granuloma formation.

Interleukin‐17 as an Effector Molecule of Innate and Acquired Immunity against Infections

Interleukin (IL)‐17 is a proinflammatory cytokine which induces differentiation and migration of neutrophils through induction of cytokines and chemokines including granulocyte‐colony stimulating factor and CXCL8/IL‐8. IL‐17‐producing CD4+ T cells (Th17) have pivotal role in pathogenesis of autoimmune diseases. IL‐17 is also involved in protective immunity against various infections. IL‐17 has important role in induction of neutrophil‐mediated protective immune response against extracellular bacterial or fungal pathogens such as Klebsiella pneumoniae and Candida albicans. Importance of IL‐17 in protection against intracellular pathogens including Mycobacterium has also been reported. Interestingly, not only CD4+ T cells but atypical CD4–CD8– T cells expressing T cell receptor (TCR) γδ produce IL‐17, and IL‐17 producing cells participate in both innate and acquired immune response to infections. Furthermore, neutrophil induction may not be the only mechanism of IL‐17‐mediated protective immunity. IL‐17 seems to participate in host defense through regulation of cell‐mediated immunity or induction of antimicrobial peptides such as β‐defensins. In this review, we summarize recent progress on the role of IL‐17 in immune response against infections, and discuss possible application of IL‐17 in prevention and treatment of infectious diseases.

Contribution of IL-17–producing γδ T cells to the efficacy of anticancer chemotherapy

IL-17 production by γδ T cells is required for tumor cell infiltration by IFN-γ–producing CD8+ T cells and inhibition of tumor growth in response to anthracyclines.

Mucosal T Cells Bearing TCRγδ Play a Protective Role in Intestinal Inflammation

Intestinal intraepithelial lymphocytes (IEL) bearing TCRγδ represent a major T cell population in the murine intestine. However, the role of γδ IEL in inflammatory bowel diseases (IBD) remains controversial. In this study, we show that γδ IEL is an important protective T cell population against IBD. γδ T cell-deficient (Cδ−/−) mice developed spontaneous colitis with age and showed high susceptibility to Th1-type 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis at a young age. Transfer of γδ IEL to Cδ−/− mice ameliorated TNBS-induced colitis, which correlated with decrease of IFN-γ and TNF-α production and an increase of TGF-β production by IEL. Furthermore, a high level of IL-15, which inhibits activation-induced cell death to terminate inflammation, was expressed more in intestinal epithelial cells (EC) from TNBS-treated Cδ−/− mice than in those from wild-type mice. EC from wild-type mice significantly suppressed the IFN-γ production of IEL from TNBS-treated Cδ−/− mice, whereas EC from TNBS-treated Cδ−/− mice did not. These data indicate that γδ IEL play important roles in controlling IBD by regulating mucosal T cell activation cooperated with EC function. Our study suggests that enhancement of regulatory γδ T cell activity is a possible new cell therapy for colitis.

Importance of murine Vδ1+γδ T cells expressing interferon-γ and interleukin-17A in innate protection against Listeria monocytogenes infection

Murine γδ T cells participate in the innate immune response against infection by an intracellular pathogen Listeria monocytogenes. Vδ1+γδ T cells coexpressing Vγ6 are a major γδ T‐cell subpopulation induced at an early stage of L. monocytogenes infection in the livers of infected mice. To investigate the protective role of the Vγ6/Vδ1+γδ T cells against L. monocytogenes infection, Vδ1 gene‐deficient (Vδ1−/−) mice were analysed because these mice selectively lacked a Vγ6/Vδ1+γδ T‐cell subpopulation in the L. monocytogenes‐infected liver. The Vδ1−/− mice showed increased bacterial burden in the liver and spleen, and decreased survival rate at an early stage of L. monocytogenes infection when compared to wild‐type mice. Histological examination showed abscess‐like lesions and unorganized distribution of macrophages in the liver of the Vδ1−/− mice but not in the wild‐type mice after L. monocytogenes infection. The Vγ6/Vδ1+γδ T cells produced interferon‐γ and interleukin‐17A. All the results suggest that murine Vγ6/Vδ1+γδ T cells control the innate protective response against L. monocytogenes infection through production of the proinflammatory cytokines interferon‐γ and interleukin‐17A in the infected liver.

IL-1 receptor antagonist-deficient mice develop autoimmune arthritis due to intrinsic activation of IL-17-producing CCR2+Vγ6+γδ T cells

Interleukin-17 (IL-17)-producing γδ T (γδ17) cells have been implicated in inflammatory diseases, but the underlying pathogenic mechanisms remain unclear. Here, we show that both CD4+ and γδ17 cells are required for the development of autoimmune arthritis in IL-1 receptor antagonist (IL-1Ra)-deficient mice. Specifically, activated CD4+ T cells direct γδ T-cell infiltration by inducing CCL2 expression in joints. Furthermore, IL-17 reporter mice reveal that the Vγ6+ subset of CCR2+ γδ T cells preferentially produces IL-17 in inflamed joints. Importantly, because IL-1Ra normally suppresses IL-1R expression on γδ T cells, IL-1Ra-deficient mice exhibit elevated IL-1R expression on Vγ6+ cells, which play a critical role in inducing them to produce IL-17. Our findings demonstrate a pathogenic mechanism in which adaptive and innate immunity induce an autoimmune disease in a coordinated manner.

Development of Dendritic Epidermal T Cells with a Skewed Diversity of γδTCRs in Vδ1-Deficient Mice

One of the most intriguing features of γδ T cells that reside in murine epithelia is the association of a specific Vγ/Vδ usage with each epithelial tissue. Dendritic epidermal T cells (DETCs) in the murine epidermis, are predominantly derived from the “first wave” Vγ5+ fetal thymocytes and overwhelmingly express the canonical Vγ5/Vδ1-TCRs lacking junctional diversity. Targeted disruption of the Vδ1 gene resulted in a markedly impaired development of Vγ5+ fetal thymocytes as precursors of DETCs; however, γδTCR+ DETCs with a typical dendritic morphology were observed in Vδ1−/− mice and their cell densities in the epidermis were slightly lower than those in Vδ1+/− epidermis. Moreover, the Vδ1-deficient DETCs were functionally competent in their ability to up-regulate cytokines and keratinocyte growth factor-expression in response to keratinocytes. Vγ5+ DETCs were predominant in the Vδ1−/− epidermis, though Vγ5− γδTCR+ DETCs were also detected. The Vγ5+ DETCs showed a typical dendritic shape, γδTCRhigh, and age-associated expansion in epidermis as observed in conventional DETCs of normal mice, whereas the Vγ5− γδTCR+ DETCs showed a less dendritic shape, γδTCRlow, and no expansion in the epidermis, consistent with their immaturity. These results suggest that optimal DETC development does not require a particular Vγ/Vδ-chain usage but requires expression of a limited diversity of γδTCRs, which allow DETC precursors to mature and expand within the epidermal microenvironment.

Interleukin-17A is required to suppress invasion of Salmonella enterica serovar Typhimurium to enteric mucosa

Salmonella enterica serovar Typhimurium (S. typhimurium) causes a localized enteric infection and its elimination is dependent on a T helper type 1 immune response. However, the mechanism of the protective immune response against the pathogen in gut‐associated lymphoid tissue (GALT) at an early stage of the infection is not yet clarified. Here, we show that interleukin‐17A (IL‐17A) was constitutively expressed in GALT; it was also detected on crypt and epithelial cells of the small intestine. Neutralization of the IL‐17A in the intestinal lumen exacerbated epithelial damage induced by intestinal S. typhimurium infection at an early stage of the infection. The result suggests that IL‐17A has a pivotal role in the immediate early stage of protection against bacterial infection at the intestinal mucosa. As IL‐17A neutralization also suppressed the constitutive localization of β‐defensin 3 (BD3), an IL‐17A‐induced antimicrobial peptide, at the apical site of the intestinal mucosa, it is estimated that IL‐17A constitutively induces the expression of the antimicrobial peptide to kill invading pathogens at the epithelial surface immediately after the infection. In contrast, interferon‐γ is induced around 3 days after S. typhimurium infection, and its expression level increases thereafter. Taken together, the findings lead to the hypothesis that IL‐17A participates in the immediate early stage of protection against S. typhimurium intestinal infection whereas interferon‐γ is important at a later stage of the infection.