Subash Babu

Host-directed therapy of tuberculosis based on interleukin-1 and type I interferon crosstalk

Tuberculosis remains second only to HIV/AIDS as the leading cause of mortality worldwide due to a single infectious agent. Despite chemotherapy, the global tuberculosis epidemic has intensified because of HIV co-infection, the lack of an effective vaccine and the emergence of multi-drug-resistant bacteria. Alternative host-directed strategies could be exploited to improve treatment efficacy and outcome, contain drug-resistant strains and reduce disease severity and mortality. The innate inflammatory response elicited by Mycobacterium tuberculosis (Mtb) represents a logical host target. Here we demonstrate that interleukin-1 (IL-1) confers host resistance through the induction of eicosanoids that limit excessive type I interferon (IFN) production and foster bacterial containment. We further show that, in infected mice and patients, reduced IL-1 responses and/or excessive type I IFN induction are linked to an eicosanoid imbalance associated with disease exacerbation. Host-directed immunotherapy with clinically approved drugs that augment prostaglandin E2 levels in these settings prevented acute mortality of Mtb-infected mice. Thus, IL-1 and type I IFNs represent two major counter-regulatory classes of inflammatory cytokines that control the outcome of Mtb infection and are functionally linked via eicosanoids. Our findings establish proof of concept for host-directed treatment strategies that manipulate the host eicosanoid network and represent feasible alternatives to conventional chemotherapy.

Regulatory Networks Induced by Live Parasites Impair Both Th1 and Th2 Pathways in Patent Lymphatic Filariasis: Implications for Parasite Persistence

Patent lymphatic filariasis is characterized by a profound down-regulation of immune responses with both parasite Ag-specific tolerance and bystander suppression. Although this down-regulation is confined to the Th1 arm of the immune system in response to parasite Ag, we hypothesized a more generalized suppression in response to live parasites. Indeed, when we examined the cytokine profile of a cohort of filaria-infected (n = 10) and uninfected (n = 10) individuals in response to live infective-stage larvae or microfilariae of Brugia malayi, we found significant impairment of both Th1 and Th2 cytokines characterized by diminished production of IFN-γ, TNF-α, IL-4, IL-5, and IL-10 in infected patients. The molecular basis of this impaired Th1/Th2 response was examined, and we identified three major networks of immunoregulation and tolerance. First, impaired induction of T-bet and GATA-3 mRNA underlies the Th1/Th2 deficiency in infected individuals. Second, regulatory networks, as evidenced by significantly increased expression of Foxp3 (natural regulatory T cell marker) and regulatory effectors such as TGF-β, CTLA-4, PD-1, ICOS, and indoleamine 2,3-dioxygenase play an important role in immunosuppression. Third, the compromise of effector T cell function is mediated by the enhanced induction of anergy-inducing factors cbl-b, c-cbl (cbl is abbreviation for Casitas B lymphoma), Itch, and Nedd4. Indeed, blocking CTLA-4 or neutralizing TGF-β restored the ability to mount Th1/Th2 responses to live parasites and reversed the induction of anergy-inducing factors. Hence, we conclude that a profound impairment of live parasite-specific Th1 and Th2 immune responses occurs in lymphatic filariasis that is governed at the transcriptional level by a complex interplay of inhibitory mediators.

Cutting Edge: Diminished T Cell TLR Expression and Function Modulates the Immune Response in Human Filarial Infection

Patent lymphatic filariasis is characterized by profound Ag-specific T cell hyporesponsiveness with impaired IFN-γ and IL-2 production. Because T cells have been shown to express a number of TLR and to respond to TLR ligands, we hypothesized that diminished T cell TLR function could partially account for the T cell hyporesponsiveness in filariasis. T cells expressed TLR1, TLR2, TLR4, and TLR9, and the baseline expression of TLR1, TLR2, and TLR4, but not TLR9 was significantly lower in T cells of the filarial-infected individuals compared with the uninfected individuals (both endemic and nonendemic). TLR function was significantly diminished in the T cells of filarial-infected individuals based on decreased T cell activation/cytokine production in response to TLR ligands. Thus, diminished expression and function of T cell TLR is a novel mechanism underlying T cell immune tolerance in lymphatic filariasis.

Diminished Expression and Function of TLR in Lymphatic Filariasis: A Novel Mechanism of Immune Dysregulation

Lymphatic filariasis is a disease characterized by immune dysregulation involving APC and T cell populations. To assess the contribution of TLR in mediating this dysregulation, we examined the expression of TLR1, TLR2, TLR4, and TLR9 on B cells and monocytes of filaria-infected and uninfected individuals. Baseline expression of TLR was significantly lower in B cells but not in monocytes of the filaria-infected group compared with the uninfected group. Upon stimulation with filarial Ag, a diminished up-regulation of TLR was observed in both B cells and monocytes of infected individuals. Finally, stimulation of B cells and monocytes with TLR ligands resulted in decreased B cell and monocyte activation/cytokine production, indicating a state of immune tolerance. This dysregulation is associated with diminished CD4+ T cell production of IFN-γ and IL-5. The diminished expression and function of TLR is thus a likely consequence of chronic Ag stimulation and could serve as a novel mechanism underlying the dysfunctional immune response in filariasis.

S100A8/A9 Proteins Mediate Neutrophilic Inflammation and Lung Pathology during Tuberculosis

RATIONALE A hallmark of pulmonary tuberculosis (TB) is the formation of granulomas. However, the immune factors that drive the formation of a protective granuloma during latent TB, and the factors that drive the formation of inflammatory granulomas during active TB, are not well defined. OBJECTIVES The objective of this study was to identify the underlying immune mechanisms involved in formation of inflammatory granulomas seen during active TB. METHODS The immune mediators involved in inflammatory granuloma formation during TB were assessed using human samples and experimental models of Mycobacterium tuberculosis infection, using molecular and immunologic techniques. MEASUREMENTS AND MAIN RESULTS We demonstrate that in human patients with active TB and in nonhuman primate models of M. tuberculosis infection, neutrophils producing S100 proteins are dominant within the inflammatory lung granulomas seen during active TB. Using the mouse model of TB, we demonstrate that the exacerbated lung inflammation seen as a result of neutrophilic accumulation is dependent on S100A8/A9 proteins. S100A8/A9 proteins promote neutrophil accumulation by inducing production of proinflammatory chemokines and cytokines, and influencing leukocyte trafficking. Importantly, serum levels of S100A8/A9 proteins along with neutrophil-associated chemokines, such as keratinocyte chemoattractant, can be used as potential surrogate biomarkers to assess lung inflammation and disease severity in human TB. CONCLUSIONS Our results thus show a major pathologic role for S100A8/A9 proteins in mediating neutrophil accumulation and inflammation associated with TB. Thus, targeting specific molecules, such as S100A8/A9 proteins, has the potential to decrease lung tissue damage without impacting protective immunity against TB.

Filarial lymphedema is characterized by antigen-specific Th1 and th17 proinflammatory responses and a lack of regulatory T cells.

Background Lymphatic filariasis can be associated with development of serious pathology in the form of lymphedema, hydrocele, and elephantiasis in a subset of infected patients. Methods and Findings To elucidate the role of CD4+ T cell subsets in the development of lymphatic pathology, we examined specific sets of cytokines in individuals with filarial lymphedema in response to parasite antigen (BmA) and compared them with responses from asymptomatic infected individuals. We also examined expression patterns of Toll-like receptors (TLR1–10) and Nod-like receptors (Nod1, Nod2, and NALP3) in response to BmA. BmA induced significantly higher production of Th1-type cytokines—IFN-γ and TNF-α—in patients with lymphedema compared with asymptomatic individuals. Notably, expression of the Th17 family of cytokines—IL-17A, IL-17F, IL-21, and IL-23—was also significantly upregulated by BmA stimulation in lymphedema patients. In contrast, expression of Foxp3, GITR, TGFβ, and CTLA-4, known to be expressed by regulatory T cells, was significantly impaired in patients with lymphedema. BmA also induced significantly higher expression of TLR2, 4, 7, and 9 as well Nod1 and 2 mRNA in patients with lymphedema compared with asymptomatic controls. Conclusion Our findings implicate increased Th1/Th17 responses and decreased regulatory T cells as well as regulation of Toll- and Nod-like receptors in pathogenesis of filarial lymphedema.

Human type 1 and 17 responses in latent tuberculosis are modulated by coincident filarial infection through cytotoxic T lymphocyte antigen-4 and programmed death-1.

Mycobacterium tuberculosis and filarial coinfection is highly prevalent, and the presence of a tissue-invasive helminth may modulate the predominant type 1 T helper (Th1; interferon [IFN]-gamma-mediated) response needed to control M. tuberculosis infection. By analyzing the cellular responses to mycobacterial antigens in patients who had latent tuberculosis with or without filarial infection, we were able to demonstrate that filarial infection coincident with M. tuberculosis infection significantly diminishes M. tuberculosis-specific Th1 (interleukin [IL]-12 and IFN-gamma) and type 17 T helper (Th17; IL-23 and IL-17) responses related to increased expression of cytotoxic T lymphocyte antigen (CTLA)-4 and programmed death (PD)-1. Blockade of CTLA-4 restored production of both IFN-gamma and IL-17, whereas PD-1 blockade restored IFN-gamma production only. Thus, coincident filarial infection exerted a profound inhibitory effect on protective mycobacteria-specific Th1 and Th17 responses in latent tuberculosis, suggesting a mechanism by which concomitant filarial (and other systemic helminth) infections predispose to the development of active tuberculosis in humans.

Increased Th1 and suppressed Th2 serum cytokine levels in subjects with diabetic coronary artery disease

BackgroundThe role played by T helper cytokines under chronic, low grade inflammation as seen in type-2 Diabetes Mellitus (T2DM) and Coronary Artery Disease (CAD) co-morbidity is less well studied. In the present study, we measured the serum levels of both Th1 and Th2 cytokines and correlated it with clinical risk factors for T2DM (Insulin Resistance (IR), Glycated haemoglobin (HbA1c)) and CAD (C-Reactive Protein (CRP), Intima Media Thickness (IMT) and Augmentation index (AGI)) in T2DM subjects with/without CAD.MethodologyThe study subjects were recruited from Chennai Urban Rural Epidemiology Study (CURES). Serum cytokine profile was determined by multiplex cytokine assay in Control (n = 61), T2DM (n = 60), CAD (n = 23) and T2DM-CAD (n = 21) subjects.ResultsT2DM subjects showed a mixed Th1-Th2 profile. CAD subjects presented a Th1 profile with modest Th2 suppression while T2DM-CAD subjects showed enhanced Th1 profile with strong suppression of Th2 cytokines. Both Th1 and Th2 cytokines showed a positive correlation with FPG, HbA1c, hsCRP, IMT and AGI. Logistic regression analysis revealed a significant association of IL-12 (OR = 9.3; 95% CI = 3.2-70.7; p = 0.016), IFN-γ (OR = 2.8; 95% CI = 2.7-2.9, p = 0.010), IL-4 (OR = 2.7; 95% CI 2.7-2.7, p = 0.010), IL-5 (OR = 1.1; 95% CI = 1.0-1.4; p = 0.003) and IL-13 (OR = 2; 95% CI = 1.7-2.6; p = 0.017) with T2DM-CAD.ConclusionIn conclusion, from the present study it appears that transition from T2DM or CAD to T2DM-CAD co-morbidity is associated with strong down regulation of Th2 cytokines and enhancement of Th1 responses.

Alternatively Activated and Immunoregulatory Monocytes in Human Filarial Infections

BACKGROUND Monocytes/macrophages from filaria-infected animals exhibit an alternatively activated phenotype; however, very little is known about the alternative activation phenotype of monocytes in human filarial infection. METHODS To elucidate the activation and cytokine profile of monocytes in human filarial infection, we examined the expression patterns of genes encoding arginase, nitric oxide synthase 2, alternative activation markers, and cytokines in monocytes from individuals with asymptomatic filarial infection and individuals without filarial infection, ex vivo and in response to filarial antigen (Brugia malayi antigen [BmA]). RESULTS Monocytes from patients with asymptomatic filarial infection exhibited significantly diminished expression of NOS2 and significantly enhanced expression of ARG1. These changes were associated with significantly increased expression of the genes encoding resistin, mannose receptor C type 1 (MRC1), macrophage galactose type C lectin (MGL), and chemokine ligand 18 (CCL18). In response to BmA, purified monocytes from infected individuals also expressed significantly lower levels of interleukin (IL)-12 and IL-18 but, in contrast, expressed significantly higher levels of transforming growth factor beta, IL-10, and suppressor of cytokine signaling 1 mRNA. Inhibition of arginase-1 resulted in significantly diminished expression of the genes encoding resistin, MRC1, MGL, and CCL18, as well as significantly enhanced expression of NOS2 and the genes encoding IL-12 and IL-18. CONCLUSION Patent human filarial infection is associated with the presence of monocytes characterized by an alternatively activated immunoregulatory phenotype.

Role of gamma interferon and interleukin-4 in host defense against the human filarial parasite Brugia malayi.

ABSTRACT We have investigated the roles of gamma interferon (IFN-γ) and interleukin-4 (IL-4) in host defense against Brugia malayi. Our data suggest that the lack of either IFN-γ or IL-4 prolongs the time required to achieve sterile immunity, suggesting that both canonical type 1 and type 2 responses are involved in the clearance of infection.