IL-9 promotes anti-Mycobacterium leprae cytotoxicity: involvement of IFNgamma

CD4+ T-Cell Senescence in Neurodegenerative Disease: Pathogenesis and Potential Therapeutic Targets

With the increasing proportion of the aging population, neurodegenerative diseases have become one of the major health issues in society. Neurodegenerative diseases (NDs), including multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), are characterized by progressive neurodegeneration associated with aging, leading to a gradual decline in cognitive, emotional, and motor functions in patients. The process of aging is a normal physiological process in human life and is accompanied by the aging of the immune system, which is known as immunosenescence. T-cells are an important part of the immune system, and their senescence is the main feature of immunosenescence. The appearance of senescent T-cells has been shown to potentially lead to chronic inflammation and tissue damage, with some studies indicating a direct link between T-cell senescence, inflammation, and neuronal damage. The role of these subsets with different functions in NDs is still under debate. A growing body of evidence suggests that in people with a ND, there is a prevalence of CD4+ T-cell subsets exhibiting characteristics that are linked to senescence. This underscores the significance of CD4+ T-cells in NDs. In this review, we summarize the classification and function of CD4+ T-cell subpopulations, the characteristics of CD4+ T-cell senescence, the potential roles of these cells in animal models and human studies of NDs, and therapeutic strategies targeting CD4+ T-cell senescence.

Comparison of Serum Levels of Interleukin 17 and Interleukin 9 in Leprosy Patients with and without Lepra Reaction: A Cross-Sectional Analytical Study from Central India

New pathways of host defence have emerged in leprosy, such as T helper (Th) -17, Th-9, T regulatory cells, and other factors like transforming growth factor-beta, etc. Interleukin (IL) 17 produced by Th17 cells has been found to be elevated in lepra reaction, especially type 2 lepra reaction (T2R). Role of IL-9 has not been studied widely in leprosy reactions so far. The study aimed to compare serum levels of IL-17 and IL-9 in leprosy patients with and without lepra reaction. This was a cross-sectional analytical study including untreated adult leprosy patients with and without lepra reaction. A total of 65 patients were included in the study with 30 leprosy patients without reaction and 35 with lepra reaction. Serum levels of IL-17 and IL-9 were measured in these patients using direct enzyme-linked immunosorbent assay and were compared. Borderline tuberculoid (BT) leprosy with type 1 and Lepromatous (LL) leprosy with T2R patients showed significantly higher levels of IL-17 than BT and LL leprosy patients without lepra reaction, respectively. LL patients with T2R showed significantly lower levels of IL-9 than lepromatous cases without reaction. IL-9 levels were higher in BT patients with T1R as compared to BT patients without reaction but the difference was not significant. We found evidence in support of role of IL-17 in the pathogenesis of T2R, which might serve as useful serum markers for the same. IL-17 might have a role in BT leprosy with T1R. IL-9 seems to have a protective role in T2R as opposed to IL-17, working in synergism with Th1 cytokines.

Upregulated Expression of the IL-9 Receptor on TRAF3-Deficient B Lymphocytes Confers Ig Isotype Switching Responsiveness to IL-9 in the Presence of Antigen Receptor Engagement and IL-4

The pleiotropic cytokine IL-9 signals to target cells by binding to a heterodimeric receptor consisting of the unique subunit IL-9R and the common subunit γ-chain shared by multiple cytokines of the γ-chain family. In the current study, we found that the expression of IL-9R was strikingly upregulated in mouse naive follicular B cells genetically deficient in TNFR-associated factor 3 (TRAF3), a critical regulator of B cell survival and function. The highly upregulated IL-9R on Traf3-/- follicular B cells conferred responsiveness to IL-9, including IgM production and STAT3 phosphorylation. Interestingly, IL-9 significantly enhanced class switch recombination to IgG1 induced by BCR crosslinking plus IL-4 in Traf3-/- B cells, which was not observed in littermate control B cells. We further demonstrated that blocking the JAK-STAT3 signaling pathway abrogated the enhancing effect of IL-9 on class switch recombination to IgG1 induced by BCR crosslinking plus IL-4 in Traf3-/- B cells. Our study thus revealed, to our knowledge, a novel pathway that TRAF3 suppresses B cell activation and Ig isotype switching by inhibiting IL-9R-JAK-STAT3 signaling. Taken together, our findings provide (to our knowledge) new insights into the TRAF3-IL-9R axis in B cell function and have significant implications for the understanding and treatment of a variety of human diseases involving aberrant B cell activation such as autoimmune disorders.

Modulation of the Response to Mycobacterium leprae and Pathogenesis of Leprosy

The initial infection by the obligate intracellular bacillus Mycobacterium leprae evolves to leprosy in a small subset of the infected individuals. Transmission is believed to occur mainly by exposure to bacilli present in aerosols expelled by infected individuals with high bacillary load. Mycobacterium leprae-specific DNA has been detected in the blood of asymptomatic household contacts of leprosy patients years before active disease onset, suggesting that, following infection, the bacterium reaches the lymphatic drainage and the blood of at least some individuals. The lower temperature and availability of protected microenvironments may provide the initial conditions for the survival of the bacillus in the airways and skin. A subset of skin-resident macrophages and the Schwann cells of peripheral nerves, two M. leprae permissive cells, may protect M. leprae from effector cells in the initial phase of the infection. The interaction of M. leprae with these cells induces metabolic changes, including the formation of lipid droplets, that are associated with macrophage M2 phenotype and the production of mediators that facilitate the differentiation of specific T cells for M. leprae-expressed antigens to a memory regulatory phenotype. Here, we discuss the possible initials steps of M. leprae infection that may lead to active disease onset, mainly focusing on events prior to the manifestation of the established clinical forms of leprosy. We hypothesize that the progressive differentiation of T cells to the Tregs phenotype inhibits effector function against the bacillus, allowing an increase in the bacillary load and evolution of the infection to active disease. Epigenetic and metabolic mechanisms described in other chronic inflammatory diseases are evaluated for potential application to the understanding of leprosy pathogenesis. A potential role for post-exposure prophylaxis of leprosy in reducing M. leprae-induced anti-inflammatory mediators and, in consequence, Treg/T effector ratios is proposed.

Advances in the Immunology and Genetics of Leprosy

Leprosy, a disease caused by the intracellular parasite Mycobacterium leprae or Mycobacterium lepromatosis, has affected humans for more than 4,000 years and is a stigmatized disease even now. Since clinical manifestations of leprosy patients present as an immune-related spectrum, leprosy is regarded as an ideal model for studying the interaction between host immune response and infection; in fact, the landscape of leprosy immune responses has been extensively investigated. Meanwhile, leprosy is to some extent a genetic disease because the genetic factors of hosts have long been considered major contributors to this disease. Many immune-related genes have been discovered to be associated with leprosy. However, immunological and genetic findings have rarely been studied and discussed together, and as a result, the effects of gene variants on leprosy immune responses and the molecular mechanisms of leprosy pathogenesis are largely unknown. In this context, we summarized advances in both the immunology and genetics of leprosy and discussed the perspective of the combination of immunological and genetic approaches in studying the molecular mechanism of leprosy pathogenesis. In our opinion, the integrating of immunological and genetic approaches in the future may be promising to elucidate the molecular mechanism of leprosy onset and how leprosy develops into different types of leprosy.

Leprosy As a Complex Infection: Breakdown of the Th1 and Th2 Immune Paradigm in the Immunopathogenesis of the Disease

Leprosy is a chronic infectious disease whose evolution involves complex immune mechanisms of the host that influence the clinical presentation of the disease. For many years, the main interpretation of the host defense response was based on characterization of the established immune paradigm between T helper (Th) 1 and Th2 lymphocytes. However, with advances in the knowledge of immunology, new approaches have emerged along with the development of new immunological pathways that have changed the interpretation of the long-established paradigm of the polar forms of the disease, especially with the identification of new subtypes of T lymphocytes such as Th9, Th17, Th22, and Tregs. Thus, this review discusses the role of these new subtypes of T helper lymphocytes and how the development of the immune response of these cells modifies the pattern of the Th1/Th2 response in the immunopathogenesis of leprosy.

Neutralization of interleukin-9 ameliorates symptoms of allergic rhinitis by reducing Th2, Th9, and Th17 responses and increasing the Treg response in a murine model

A novel independent Th-cell subset, characterized by high expression of interleukin (IL)-9, has been recognized as the "Th9" subset. Although Th9 cells are important in many diseases, their contribution to allergic rhinitis (AR) remains unclear. We therefore first determined whether Th9 cells were present in a mouse model of AR. We then investigated the their involvement in the distribution of CD4+ T-cell subsets and the symptoms of AR by treating mice with anti-IL-9 antibodies (Abs). Anti-IL-9 Abs were administered intranasally during rechallenge of ovalbumin (OVA)-induced AR in BALB/c mice. We measured nasal rubbing motion, sneezing and eosinophils, as well as the Th1 (Th1 cell percentage, Ifn-γ mRNA/protein, T-bet mRNA), Th2 (Th2 cell percentage, Il-4 mRNA/protein, Gata3 mRNA), Th9 (Th9 cell percentages Il-9 mRNA/protein, PU.1 and Irf4 mRNA), Th17 (Th17 cell percentage, Il-17 mRNA/protein, Rorγt mRNA), and Treg (Treg cell percentage, Foxp3 mRNA) responses in the nasal mucosa. Treatment with anti-IL-9 Abs markedly reduced nasal rubbing, sneezing, eosinophil infiltration, and Th2, Th9, and Th17 responses, and increased the Treg response. Our findings emphasize the importance of IL-9/Th9 in the pathogenesis of AR, and suggest that anti-IL-9 Ab treatment may be an effective therapeutic strategy for AR.

Th9 cytokines response and its possible implications in the immunopathogenesis of leprosy

AIMS

Leprosy is an infectious-contagious disease whose clinical evolution depends on the interaction of the infectious agent with the immune response of the host, leading to a clinical spectrum that ranges from lepromatous leprosy (susceptibility, LL) to tuberculoid leprosy (resistance, TT). The immune response profile will depend on the pattern of cytokine production and on the activity of macrophages during infection. Classically, the clinical evolution of leprosy has been associated with Th1/Th2 cytokine profiles, but the role of new cytokine profiles such as T helper 9 (Th9) remains to be elucidated.

METHODS

To evaluate the tissue expression profile of these cytokines, a cross-sectional study was conducted using a sample of 30 leprosy skin lesion biopsies obtained from patients with leprosy, 16 TT and 14 lepromatous LL.

RESULTS

Immunohistochemical analysis revealed a significant difference in interleukin (IL)-9, IL-4 transforming growth factor (TGF)-β and IL-10 levels between the two groups. IL-9 was more expressed in TT lesions compared with LL lesions. Higher expression of IL-4, IL-10 and TGF-β was observed in LL compared with TT. IL-4, IL-10 and TGF-β tended to be negatively correlated with the expression of IL-9, indicating a possible antagonistic activity in tissue.

CONCLUSIONS

The results suggest that Th9 lymphocytes may be involved in the response to Mycobacterium leprae, positively or negatively regulating microbicidal activity of the local immune system in the disease.

Leprosy as a model to understand cancer immunosurveillance and T cell anergy

Leprosy is a disease caused by Mycobacterium leprae that presents on a spectrum of both clinical manifestations and T cell response. On one end of this spectrum, tuberculoid leprosy is a well-controlled disease, characterized by a cell-mediated immunity and immunosurveillance. On the opposite end of the spectrum, lepromatous leprosy is characterized by M. leprae proliferation and T cell anergy. Similar to progressive tumor cells, M. leprae escapes immunosurveillance in more severe forms of leprosy. The mechanisms by which M. leprae is able to evade the host immune response involve many, including the alterations of lipid droplets, microRNA, and Schwann cells, and involve the regulation of immune regulators, such as the negative checkpoint regulators CTLA-4, programmed death 1, and V-domain Ig suppressor of T cell activation-important targets in today's cancer immunotherapies. The means by which tumor cells become able to escape immunosurveillance through negative checkpoint regulators are evidenced by the successes of treatments, such as nivolumab and ipilimumab. Many parallels can be drawn between the immune responses seen in leprosy and cancer. Therefore, the understanding of how M. leprae encourages immune escape during proliferative disease states has potential to add to our understanding of cancer immunotherapy.

Chlamydial lung infection induces transient IL-9 production which is redundant for host defense against primary infection

IL-9/Th9 responses are recently found to be important for innate and adaptive immunity particularly in parasitic infections. To date, the study on the role of IL-9 in bacterial infections is limited and the reported data are contradictory. One reported function of IL-9/Th9 is to modulate Th1/Th17 responses. Since our and others’ previous work has shown a critical role of Th1 and Th17 cells in host defense against chlamydial lung infection, we here examined the role of IL-9 responses in Chlamydia muridarum (Cm) lung infection, particularly its effect on Th1 and Th17 responses and outcome infection. Our data showed quick but transient IL-9 production in the lung following infection, peaking at day 3 and back to baseline around day 7. CD4+ T cell was the major source of IL-9 production in the lung infection. Blockade of endogenous IL-9 using neutralizing antibody failed to change Interferon-γ (IFN-γ) and IL-17 production by cultured spleen mononuclear cells isolated from Cm infected mice. Similarly, in vivo neutralization of IL-9 failed to show significant effect on T cell (Th1 and Th17) and antibody responses (IgA, IgG1 and IgG2a). Consistently, the neutralization of IL-9 had no significant effect on disease process, including body weight change, bacterial burden and histopathological score. The data suggest that IL-9 production following chlamydial lung infection is redundant for host defense against the intracellular bacteria.

Neutralization of interleukin-9 ameliorates symptoms of experimental autoimmune myasthenia gravis in rats by decreasing effector T cells and altering humoral responses

Interleukin-9 (IL-9) was initially thought to be a type 2 T helper (Th2)-associated cytokine involved in the regulation of autoimmune responses by affecting multiple cell types. However, it was recently shown that IL-9-producing CD4+ T cells represent a discrete subset of Th cells, designated Th9 cells. Although Th9 cells have been shown to be important in many diseases, their roles in myasthenia gravis (MG) are unclear. The aim of this study was to determine whether IL-9 and Th9 cells promote the progression of experimental autoimmune myasthenia gravis (EAMG). The results showed that the percentage of Th9 cells changed during the progression of EAMG, accompanied by an up-regulation of IL-9. Blocking IL-9 activity with antibodies against IL-9 inhibited EAMG-associated pathology in rats and reduced serum anti-acetylcholine receptor IgG levels. Neutralization of IL-9 altered the Th subset distribution in EAMG, reducing the number of Th1 cells and increasing the number of regulatory T cells. Administration of an anti-IL-9 antibody may represent an effective therapeutic strategy for MG-associated pathologies or other T-cell- or B-cell-mediated autoimmune diseases.

IL-9 regulates allergen-specific Th1 responses in allergic contact dermatitis

The cytokine IL-9, derived primarily from T-helper 9 (Th9) lymphocytes, promotes expansion of the Th2 subset and is implicated in the mechanisms of allergic asthma. We hypothesize that IL-9 also has a role in human allergic contact dermatitis (ACD). To investigate this hypothesis, skin biopsy specimens of positive patch-test sites from non-atopic patients were assayed using quantitative PCR and immunohistochemistry. The cytokines IFN-γ, IL-4, IL-17A, IL-9, and PU.1, a Th9 associated transcription factor, were elevated when compared with paired normal skin. Immunohistochemistry on ACD skin biopsies identified PU.1+ CD3+ and PU.1+ CD4+ cells, consistent with Th9 lymphocytes, in the inflammatory infiltrate. Peripheral blood mononuclear cells from nickel-allergic patients, but not nonallergic controls, show significant IL-9 production in response to nickel. Blocking studies with mAbs to HLA-DR (but not HLA-A, -B, -C) or chloroquine significantly reduced this nickel-specific IL-9 production. In addition, blockade of IL-9 or IL-4 enhanced allergen-specific IFN-γ production. A contact hypersensitivity model using IL-9(-/-) mice shows enhanced Th1 lymphocyte immune responses, when compared with wild-type mice, consistent with our human in vitro data. This study demonstrates that IL-9, through its direct effects on Th1 and ability to promote IL-4 secretion, has a regulatory role for Th1 lymphocytes in ACD.

Neutralization of IL-9 ameliorates experimental autoimmune encephalomyelitis by decreasing the effector T cell population

Multiple sclerosis is a CD4(+) T cell-mediated autoimmune disease affecting the CNS. Multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), have been thought to be Th1-mediated diseases. However, recent studies provide strong evidence that the major pathogenic T cell subsets in EAE are Th17 cells. IL-9, a hematopoietic growth factor, is considered to be a mediator of Th17 cells, but the precise mechanisms of its action are largely unknown. The present study was designed to investigate the role of IL-9 in autoimmune demyelination. IL-9 blockade with anti-IL-9 mAb inhibited the development of EAE, reduced the serum levels of IL-17, the CNS mRNA expression of IL-17, IL-6, IFN-γ, and TNF-α, and the myelin oligodendrocyte glycoprotein (MOG)-induced IL-17, IFN-γ secretion of lymphocytes. Furthermore, anti-IL-9 mAb in culture suppressed IL-17 production of MOG-reactive T cells and their potency in adoptive transfer EAE. These findings indicate that the protective effect of IL-9 blockade in EAE was likely mediated via inhibition of the development of MOG peptide-specific T cells, which in turn led to reduced infiltration of T cells into the CNS. Thus, anti-IL-9 mAb treatment may provide an effective therapeutic strategy against autoimmune diseases.

IL-9: basic biology, signaling pathways in CD4+ T cells and implications for autoimmunity

CD4(+) T cell subsets play an important role in the adaptive immune response in human autoimmune diseases and in animal models of autoimmunity. In recent years, our knowledge of CD4(+) T cell differentiation has increased significantly, and new subsets continue to be recognized. Of significant importance is the recent discovery of Th9 cells, the CD4 + T cell subset that produces Interleukin-9. IL-9 has largely been regarded as a Th2 cytokine; however, it is now known that under specific conditions, Tregs, Th1, Th17 and the Th9 subset of T cells also produce IL-9. The STAT family of proteins plays a major role in the signaling pathways of these CD4(+)T subsets. Biological actions of IL-9 and the STATs signaling pathways in autoimmune diseases are continuing to be clarified. Investigation of IL-9-producing CD4(+)T cells, and elucidation of the mechanisms of IL-9-induced STATs signaling, in concert with other transcription factors, will provide a better understanding of the pathogenesis of various autoimmune diseases.