Stephen J. Lalor

Interleukin-1 and IL-23 Induce Innate IL-17 Production from γδ T Cells, Amplifying Th17 Responses and Autoimmunity

Th17 cells, CD4(+) T cells that secrete interleukin-17 (IL-17), are pathogenic in autoimmune diseases and their development and expansion is driven by the cytokines IL-6, TGF-beta, IL-21, IL-1, and IL-23. However, there are also innate sources of IL-17. Here, we show that gammadelta T cells express IL-23R and the transcription factor RORgammat and produce IL-17, IL-21, and IL-22 in response to IL-1beta and IL-23, without T cell receptor engagement. IL-17-producing gammadelta T cells were found at high frequency in the brain of mice with experimental autoimmune encephalomyelitis (EAE). gammadelta T cells activated by IL-1beta and IL-23 promoted IL-17 production by CD4(+) T cells and increased susceptibility to EAE, suggesting that gammadelta T cells act in an amplification loop for IL-17 production by Th17 cells. Our findings demonstrate that gammadelta T cells activated by IL-1beta and IL-23 are an important source of innate IL-17 and IL-21 and provide an alternative mechanism whereby IL-1 and IL-23 may mediate autoimmune inflammation.

T cells in multiple sclerosis and experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is a demyelinating inflammatory disorder of the central nervous system (CNS), which involves autoimmune responses to myelin antigens. Studies in experimental autoimmune encephalomyelitis (EAE), an animal model for MS, have provided convincing evidence that T cells specific for self‐antigens mediate pathology in these diseases. Until recently, T helper type 1 (Th1) cells were thought to be the main effector T cells responsible for the autoimmune inflammation. However more recent studies have highlighted an important pathogenic role for CD4+ T cells that secrete interleukin (IL)‐17, termed Th17, but also IL‐17‐secreting γδ T cells in EAE as well as other autoimmune and chronic inflammatory conditions. This has prompted intensive study of the induction, function and regulation of IL‐17‐producing T cells in MS and EAE. In this paper, we review the contribution of Th1, Th17, γδ, CD8+ and regulatory T cells as well as the possible development of new therapeutic approaches for MS based on manipulating these T cell subtypes.

Infiltration of Th1 and Th17 cells and activation of microglia in the CNS during the course of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a mouse model for multiple sclerosis, where disease is mediated by autoantigen-specific T cells. Although there is evidence linking CD4(+) T cells that secrete IL-17, termed Th17 cells, and IFN-gamma-secreting Th1 cells with the pathogenesis of EAE, the precise contribution of these T cell subtypes or their associated cytokines is still unclear. We have investigated the infiltration of CD4(+) T cells that secrete IFN-gamma, IL-17 or both cytokines into CNS during development of EAE and have examined the role of T cells in microglial activation. Our findings demonstrate that Th17 cells and CD4(+) T cells that produce both IFN-gamma and IL-17, which we have called Th1/Th17 cells, infiltrate the brain prior to the development of clinical symptoms of EAE and that this coincides with activation of CD11b(+) microglia and local production of IL-1beta, TNF-alpha and IL-6 in the CNS. In contrast, significant infiltration of Th1 cells was only detected after the development of clinical disease. Co-culture experiments, using mixed glia and MOG-specific T cells, revealed that T cells that secreted IFN-gamma and IL-17 were potent activators of pro-inflammatory cytokines but T cells that secrete IFN-gamma, but not IL-17, were less effective. In contrast both Th1 and Th1/Th17 cells enhanced MHC-class II and co-stimulatory molecule expression on microglia. Our findings suggest that T cells which secrete IL-17 or IL-17 and IFN-gamma infiltrate the CNS prior to the onset of clinical symptoms of EAE, where they may mediate CNS inflammation, in part, through microglial activation.

Caspase-1–Processed Cytokines IL-1β and IL-18 Promote IL-17 Production by γδ and CD4 T Cells That Mediate Autoimmunity

IL-1β plays a critical role in promoting IL-17 production by γδ and CD4 T cells. However, IL-1–targeted drugs, although effective against autoinflammatory diseases, are less effective against autoimmune diseases. Conversely, gain-of-function mutations in the NLRP3 inflammasome complex are associated with enhanced IL-1β and IL-18 production and Th17 responses. In this study, we examined the role of caspase-1–processed cytokines in IL-17 production and in induction of experimental autoimmune encephalomyelitis (EAE). Killed Mycobacterium tuberculosis, the immunostimulatory component in CFA used for inducing EAE, stimulated IL-1β and IL-18 production by dendritic cells through activation of the inflammasome complex and caspase-1. Dendritic cells stimulated with M. tuberculosis and myelin oligodendrocyte glycoprotein promoted IL-17 production by T cells and induced EAE following transfer to naive mice, and this was suppressed by a caspase-1 inhibitor and reversed by administration of IL-1β or IL-18. Direct injection of the caspase-1 inhibitor suppressed IL-17 production by CD4 T cells and γδ T cells in vivo and attenuated the clinical signs of EAE. γδ T cells expressed high levels of IL-18R and the combination of IL-18 and IL-23, as with IL-1β and IL-23, stimulated IL-17 production by γδ T cells, but also from CD4 T cells, in the absence of TCR engagement. Our findings demonstrate that caspase-1–processed cytokines IL-1β and IL-18 not only promote autoimmunity by stimulating innate IL-17 production by T cells but also reveal redundancy in the functions of IL-1β and IL-18, suggesting that caspase-1 or the inflammasome may be an important drug target for autoimmune diseases.

Inhibition of ERK MAPK Suppresses IL-23- and IL-1-Driven IL-17 Production and Attenuates Autoimmune Disease

IL-17-producing CD4+ T (Th17) cells are pathogenic in many autoimmune diseases. The induction and expansion of Th17 cells is directed by cytokines, including IL-23 and IL-1β, produced by innate immune cells through activation of pathogen recognition receptors. The NF-κB and IFN regulatory factor families of transcriptional factors mediate IL-12 production; however, distinct signaling pathways appear to be required for IL-23 production. In this study, we show that inhibition of ERK MAPK suppressed IL-23 and IL-1β production by dendritic cells stimulated with TLR or dectin-1 agonists but did not affect IL-12p70 production. Furthermore, an ERK inhibitor suppressed the ability of Ag-pulsed TLR-activated dendritic cells to induce Ag-specific Th17 cells in vivo, but interestingly also inhibited the induction of Th1 cells. Treatment with an ERK inhibitor attenuated experimental autoimmune encephalomyelitis (EAE), when administered either at the induction phase of acute EAE or during remission in the relapsing-remitting EAE model. This was associated with significant suppression of autoantigen-specific Th17 and Th1 responses. The suppressive effect of the ERK inhibitor on attenuation of EAE was reversed by administration of IL-1β and IL-23. Our findings suggest that ERK MAPK plays a critical and hitherto undescribed role in activating innate production of IL-23 and IL-1β, which promote pathogenic T cell responses, and therefore represents an important target for therapeutic intervention against autoimmune diseases.

Staphylococcus aureus Infection of Mice Expands a Population of Memory γδ T Cells That Are Protective against Subsequent Infection

The development of vaccines against Staphylococcus aureus has consistently failed in clinical trials, likely due to inefficient induction of cellular immunity. T cell–derived IL-17 is one of the few known correlates of antistaphylococcoal immunity, conferring protection against S. aureus infections through its ability to promote phagocytic cell effector functions. A comprehensive understanding of the discrete T cell subsets critical for site-specific IL-17–mediated bacterial clearance will therefore be necessary to inform the development of vaccines that efficiently target cellular immunity. In this study, we have identified a population of CD44+CD27− memory γδ T cells, expanded upon infection of C57BL/6 mice with S. aureus, which produce high levels of IL-17 and mediate enhanced bacterial clearance upon reinfection with the bacterium. These cells are comprised largely of the Vγ4+ subset and accumulate at the site of infection subsequent to an initial Vγ1.1+ and Vγ2+ T cell response. Moreover, these Vγ4+ T cells are retained in the peritoneum and draining mediastinal lymph nodes for a prolonged period following bacterial clearance. In contrast to its critical requirement for γδ T cell activation during the primary infection, IL-1 signaling was dispensable for activation and expansion of memory γδ T cells upon re-exposure to S. aureus. Our findings demonstrate that a γδ T cell memory response can be induced upon exposure to S. aureus, in a fashion analogous to that associated with classical αβ T cells, and suggest that induction of IL-17–expressing γδ T cells may be an important property of a protective vaccine against S. aureus.

Memory Th1 Cells Are Protective in Invasive Staphylococcus aureus Infection.

Mechanisms of protective immunity to Staphylococcus aureus infection in humans remain elusive. While the importance of cellular immunity has been shown in mice, T cell responses in humans have not been characterised. Using a murine model of recurrent S. aureus peritonitis, we demonstrated that prior exposure to S. aureus enhanced IFNγ responses upon subsequent infection, while adoptive transfer of S. aureus antigen-specific Th1 cells was protective in naïve mice. Translating these findings, we found that S. aureus antigen-specific Th1 cells were also significantly expanded during human S. aureus bloodstream infection (BSI). These Th1 cells were CD45RO+, indicative of a memory phenotype. Thus, exposure to S. aureus induces memory Th1 cells in mice and humans, identifying Th1 cells as potential S. aureus vaccine targets. Consequently, we developed a model vaccine comprising staphylococcal clumping factor A, which we demonstrate to be an effective human T cell antigen, combined with the Th1-driving adjuvant CpG. This novel Th1-inducing vaccine conferred significant protection during S. aureus infection in mice. This study notably advances our understanding of S. aureus cellular immunity, and demonstrates for the first time that a correlate of S. aureus protective immunity identified in mice may be relevant in humans.

Memory γδ T Cells–Newly Appreciated Protagonists in Infection and Immunity

Despite the potential for diversity in their T cell receptor, γδ T cells are primarily considered to be innate immune cells. Recently, memory-like γδ T cell responses have been identified in murine models of infection and autoimmunity. Similar memory responses have also been described in human and non-human primate γδ T cells. It has thus become clear that subpopulations of γδ T cells can develop long-lasting memory akin to conventional αβ T cells, with protective and pathogenic consequences. Hence, a re-evaluation of their true capabilities and role in infection and immunity is required. This review discusses recent reports of memory-type responses attributed to γδ T cells and assesses this underappreciated facet of these enigmatic cells.

The circadian protein BMAL1 in myeloid cells is a negative regulator of allergic asthma

Our body clock drives rhythms in the expression of genes that have a 24-h periodicity. The transcription factor BMAL1 is a crucial component of the molecular clock. A number of physiological processes, including immune function, are modulated by the circadian clock. Asthma, a disease with very strong clinical evidence demonstrating regulation by circadian variation, is of particular relevance to circadian control of immunity. Airway hypersensitivity and asthma attacks are more common at night in humans. The molecular basis for this is unknown, and there is no model of asthma in animals with genetic distortion of the molecular clock. We used mice lacking BMAL1 in myeloid cells (BMAL1-LysM-/-) to determine the role of BMAL1 in allergic asthma. Using the ovalbumin model of allergic asthma, we demonstrated markedly increased asthma features, such as increased lung inflammation, demonstrated by drastically higher numbers of eosinophils and increased IL-5 levels in the lung and serum, in BMAL1-LysM-/- mice. In vitro studies demonstrated increased proinflammatory chemokine and mannose receptor expression in IL-4- as well as LPS-treated macrophages from BMAL1-LysM-/- mice compared with wild-type controls. This suggests that Bmal1 is a potent negative regulator in myeloid cells in the context of allergic asthma. Our findings might explain the increase in asthma incidents during the night, when BMAL1 expression is low.

Correction: Staphylococcus aureus Infection of Mice Expands a Population of Memory γδ T Cells That Are Protective against Subsequent Infection

Murphy, A. G., K. M. O’Keeffe, S. J. Lalor, B. M. Maher, K. H. G. Mills, and R. M. McLoughlin. 2014. Staphylococcus aureus infection of mice expands a population of memory γδ T cells that are protective against subsequent infection. J. Immunol. 192: [3697–3708][1]. In Supplemental Fig. 1F,