Masayuki Umemura

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.

Vestibular and Cochlear Toxicity of Aminoglycosides - A review

Recently, there have been many reports describing the efficacy of intratympanic aminoglycoside injection for the treatment of intractable vertigo in patients with Ménières disease. However, the number of injections and the amount of drug injected varies, with concomitant variation in the side-effect of hearing deterioration. To identify drugs that are more selectively vestibulotoxic, we have reviewed the ototoxicity of aminoglycosides, focusing on differences between vestibulo- and cochleotoxicity. At present, the basis for the different effects of each drug is unknown. The mechanisms of vestibulo- and cochleotoxicity are deemed worthy of further study.Recently, there have been many reports describing the efficacy of intratympanic aminoglycoside injection for the treatment of intractable vertigo in patients with Ménières disease. However, the number of injections and the amount of drug injected varies, with concomitant variation in the side-effect of hearing deterioration. To identify drugs that are more selectively vestibulotoxic, we have reviewed the ototoxicity of aminoglycosides, focusing on differences between vestibulo- and cochleotoxicity. At present, the basis for the different effects of each drug is unknown. The mechanisms of vestibulo- and cochleotoxicity are deemed worthy of further study.

Overexpression of IL-15 In Vivo Enhances Protection Against Mycobacterium bovis Bacillus Calmette-Guérin Infection Via Augmentation of NK and T Cytotoxic 1 Responses

To investigate the immunomodulating effects of IL-15 in vivo on mycobacterial infection, we used IL-15-transgenic (Tg) mice, which were recently constructed with cDNA-encoding secretable isoform of IL-15 precursor protein under the control of a MHC class I promoter. The IL-15-Tg mice exhibited resistance against infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG), as assessed by bacteria growth. IFN-γ level in serum was significantly higher in IL-15-Tg mice than in non-Tg mice after BCG infection. NK cells were remarkably increased, and Ag-specific T cytotoxic 1 response mediated by CD8+ T cells producing IFN-γ was significantly augmented in the IL-15-Tg mice following BCG infection. Neutralization of endogenous IFN-γ by in vivo administration of anti-IFN-γ mAb deteriorated the clearance of the bacteria. Depletion of of NK cells or CD8+ T cells by invivo administration of anti-asialo-GM1 Ab or anti-CD8 mAb hampered the exclusion of bacteria. Thus, overexpression of IL-15 in vivo enhanced protection against BCG infection via augmentation of NK and T cytotoxic 1 responses.

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.

Pathogen-Associated Molecular Patterns Sensitize Macrophages to Fas Ligand-Induced Apoptosis and IL-1β Release

Antigenic stimulation activates T cells and simultaneously destines them to die by Fas-mediated apoptosis. In this study, we demonstrated that various pathogen-associated molecular patterns up-regulated Fas expression in macrophages and sensitized them specifically to Fas ligand (FasL), but not to other apoptosis-inducing agents such as TNF-α, etoposide (VP-16), and staurosporine. Toll-like receptor, NF-κB, and p38 mitogen-activated protein kinase mediated these responses. LPS stimulation induced the expression of Fas, caspase 8, cellular FLIP Bfl-1/A1, and Bcl-x, but not FasL, TNFR p55, Bak, Bax, and Bad at the transcriptional level. Thus, LPS selectively induced the expression of apoptotic molecules of the Fas death pathway (except for cellular FLIP) and antiapoptotic molecules of the mitochondrial death pathway. However, the kinetics of macrophage disappearance following Escherichia coli-induced peritonitis was similar between wild-type and Fas-deficient mice, suggesting that Fas is not essential for the turnover of activated macrophages in T cell-independent inflammation. In contrast, LPS-activated macrophages produced a large amount of IL-1β upon FasL stimulation. Thus, unlike the activation-induced cell death of T cells, the sensitization of macrophages to FasL by pathogen-associated molecular patterns seems to be a proinflammatory rather than an anti-inflammatory event.

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.

Interleukin-15 as an immune adjuvant to increase the efficacy of Mycobacterium bovis bacillus Calmette-Guérin vaccination.

ABSTRACT Interleukin-15 (IL-15) transgenic mice which had been inoculated with Mycobacterium bovis bacillus Calmette-Guérin (BCG) 24 weeks previously showed resistance against airborne infection with Mycobacterium tuberculosis H37Rv accompanied by an increased CD8+-Tc1-cell response. IL-15 may be used as an immune adjuvant given with BCG vaccination to enhance its biologic efficacy.