Anupriya Khare

Early infection with respiratory syncytial virus impairs regulatory T cell function and increases susceptibility to allergic asthma.

Immune tolerance is instituted early in life, during which time regulatory T (Treg) cells have an important role. Recurrent infections with respiratory syncytial virus (RSV) in early life increase the risk for asthma in adult life. Repeated infection of infant mice tolerized to ovalbumin (OVA) through their mothers milk with RSV induced allergic airway disease in response to OVA sensitization and challenge, including airway inflammation, hyper-reactivity and higher OVA-specific IgE, as compared to uninfected tolerized control mice. Virus infection induced GATA-3 expression and T helper type 2 (TH2) cytokine production in forkhead box P3 (FOXP3)+ Treg cells and compromised the suppressive function of pulmonary Treg cells in a manner that was dependent on interleukin-4 receptor α (IL-4Rα) expression in the host. Thus, by promoting a TH2-type inflammatory response in the lung, RSV induced a TH2-like effector phenotype in Treg cells and attenuated tolerance to an unrelated antigen (allergen). Our findings highlight a mechanism by which viral infection targets a host-protective mechanism in early life and increases susceptibility to allergic disease.

Regulatory T Cells in Many Flavors Control Asthma

That regulatory T cells (Tregs) have a crucial role in controlling allergic diseases such as asthma is now undisputed. The cytokines most commonly implicated in Treg-mediated suppression of allergic asthma are transforming growth factor-β (TGF-β) and interleukin (IL)-10). In addition to naturally occurring Tregs, adaptive Tregs, induced in response to foreign antigens, have been shown in recent studies. The concept of inducible/adaptive Tregs (iTregs) has considerable significance in preventing asthma if generated early enough in life. This is because cytokines such as IL-4 and IL-6 inhibit Foxp3 induction in naive CD4+ T cells and therefore de novo generation of Tregs can be expected to be less efficient when it is concomitant with effector cell development in response to an allergen. However, if iTregs can be induced, the process of infectious tolerance would facilitate expansion of the iTreg pool as suggested in the recent literature. It is tempting to speculate that there is a window of opportunity in early life in the context of a relatively immature immune system that is permissive for the generation of iTregs specific to a spectrum of allergens that would regulate asthma for lifelong. The focus of this review is the relevance of nTregs and iTregs in controlling asthma from early life into adulthood, the mechanisms underlying Treg function, and the prospects for using our current concepts to harness the full potential of Tregs to limit disease development and progression.

TNF-alpha from inflammatory dendritic cells (DCs) regulates lung IL-17A/IL-5 levels and neutrophilia versus eosinophilia during persistent fungal infection.

Aspergillus fumigatus is commonly associated with allergic bronchopulmonary aspergillosis in patients with severe asthma in which chronic airway neutrophilia predicts a poor outcome. We were able to recapitulate fungus-induced neutrophilic airway inflammation in a mouse model in our efforts to understand the underlying mechanisms. However, neutrophilia occurred in a mouse strain-selective fashion, providing us with an opportunity to perform a comparative study to elucidate the mechanisms involved. Here we show that TNF-α, largely produced by Ly6c+CD11b+ dendritic cells (DCs), plays a central role in promoting IL-17A from CD4+ T cells and collaborating with it to induce airway neutrophilia. Compared with C57BL/6 mice, BALB/c mice displayed significantly more TNF-α–producing DCs and macrophages in the lung. Lung TNF-α levels were drastically reduced in CD11c-DTR BALB/c mice depleted of CD11c+ cells, and TNF-α–producing Ly6c+CD11b+ cells were abolished in Dectin-1−/− and MyD88−/− BALB/c mice. TNF-α deficiency itself blunted accumulation of inflammatory Ly6c+CD11b+ DCs. Also, lack of TNF-α decreased IL-17A but promoted IL-5 levels, switching inflammation from a neutrophil to eosinophil bias resembling that in C57BL/6 mice. The TNF-αlow DCs in C57BL/6 mice contained more NF-κB p50 homodimers, which are strong repressors of TNF-α transcription. Functionally, collaboration between TNF-α and IL-17A triggered significantly higher levels of the neutrophil chemoattractants keratinocyte cytokine and macrophage inflammatory protein 2 in BALB/c mice. Our study identifies TNF-α as a molecular switch that orchestrates a sequence of events in DCs and CD4 T cells that promote neutrophilic airway inflammation.

High IFN-γ and low SLPI mark severe asthma in mice and humans

Severe asthma (SA) is a challenge to control, as patients are not responsive to high doses of systemic corticosteroids (CS). In contrast, mild-moderate asthma (MMA) is responsive to low doses of inhaled CS, indicating that Th2 cells, which are dominant in MMA, do not solely orchestrate SA development. Here, we analyzed broncholalveolar lavage cells isolated from MMA and SA patients and determined that IFN-γ (Th1) immune responses are exacerbated in the airways of individuals with SA, with reduced Th2 and IL-17 responses. We developed a protocol that recapitulates the complex immune response of human SA, including the poor response to CS, in a murine model. Compared with WT animals, Ifng-/- mice subjected to this SA model failed to mount airway hyperresponsiveness (AHR) without appreciable effect on airway inflammation. Conversely, AHR was not reduced in Il17ra-/- mice, although airway inflammation was lower. Computer-assisted pathway analysis tools linked IFN-γ to secretory leukocyte protease inhibitor (SLPI), which is expressed by airway epithelial cells, and IFN-γ inversely correlated with SLPI expression in SA patients and the mouse model. In mice subjected to our SA model, forced SLPI expression decreased AHR in the absence of CS, and it was further reduced when SLPI was combined with CS. Our study identifies a distinct immune response in SA characterized by a dysregulated IFN-γ/SLPI axis that affects lung function.

Cutting Edge: Inhaled Antigen Upregulates Retinaldehyde Dehydrogenase in Lung CD103 + but Not Plasmacytoid Dendritic Cells To Induce Foxp3 De Novo in CD4 + T Cells and Promote Airway Tolerance

Dendritic cell (DC)–T cell interactions that underlie inducible/adaptive regulatory T cell generation and airway tolerance are not well understood. In this study, we show that mice lacking CD11chi lung DCs, but containing plasmacytoid DCs (pDCs), fail tolerization with inhaled Ag and cannot support Foxp3 induction in vivo in naive CD4+ T cells. CD103+ DCs from tolerized mice efficiently induced Foxp3 in cocultured naive CD4+ T cells but pDCs and lung macrophages failed to do so. CD103+ DCs, but not pDCs or lung macrophages, upregulated the expression of retinaldehyde dehydrogenase 2 (aldh1a2), which is key for the production of retinoic acid, a cofactor for TGF-β for Foxp3 induction. Batf3−/− mice, selectively lacking CD103+ DCs, failed tolerization by inhaled Ag. Collectively, our data show that pulmonary tolerance is dependent on CD103+ DCs, correlating with their ability to upregulate aldh1a2, which can promote Foxp3 expression in T cells.

STAT1-regulated lung MDSC-like cells produce IL-10 and efferocytose apoptotic neutrophils with relevance in resolution of bacterial pneumonia

Bacterial pneumonia remains a significant burden worldwide. Although an inflammatory response in the lung is required to fight the causative agent, persistent tissue-resident neutrophils in non-resolving pneumonia can induce collateral tissue damage and precipitate acute lung injury. However, little is known about mechanisms orchestrated in the lung tissue that remove apoptotic neutrophils to restore tissue homeostasis. In mice infected with Klebsiella pneumoniae, a bacterium commonly associated with hospital-acquired pneumonia, we show that interleukin (IL)-10 is essential for resolution of lung inflammation and recovery of mice after infection. Although IL-10−/− mice cleared bacteria, they displayed increased morbidity with progressive weight loss and persistent lung inflammation in the later phase after infection. A source of tissue IL-10 was found to be resident CD11b+Gr1intF4/80+ cells resembling myeloid-derived suppressor cells (MDSCs) that appeared with a delayed kinetics after infection. These cells efficiently efferocytosed apoptotic neutrophils, which was aided by IL-10. The lung neutrophil burden was attenuated in infected signal transducer and activator of transcription 1 (STAT1)−/− mice with concomitant increase in the frequency of the MDSC-like cells and lung IL-10 levels. Thus, inhibiting STAT1 in combination with antibiotics may be a novel therapeutic strategy to address inefficient resolution of bacterial pneumonia.

Pulmonary receptor for advanced glycation end-products promotes asthma pathogenesis through IL-33 and accumulation of group 2 innate lymphoid cells.

BACKGROUND Single nucleotide polymorphisms in the human gene for the receptor for advanced glycation end-products (RAGE) are associated with an increased incidence of asthma. RAGE is highly expressed in the lung and has been reported to play a vital role in the pathogenesis of murine models of asthma/allergic airway inflammation (AAI) by promoting expression of the type 2 cytokines IL-5 and IL-13. IL-5 and IL-13 are prominently secreted by group 2 innate lymphoid cells (ILC2s), which are stimulated by the proallergic cytokine IL-33. OBJECTIVE We sought to test the hypothesis that pulmonary RAGE is necessary for allergen-induced ILC2 accumulation in the lung. METHODS AAI was induced in wild-type and RAGE knockout mice by using IL-33, house dust mite extract, or Alternaria alternata extract. RAGEs lung-specific role in type 2 responses was explored with bone marrow chimeras and induction of gastrointestinal type 2 immune responses. RESULTS RAGE was found to drive AAI by promoting IL-33 expression in response to allergen and by coordinating the inflammatory response downstream of IL-33. Absence of RAGE impedes pulmonary accumulation of ILC2s in models of AAI. Bone marrow chimera studies suggest that pulmonary parenchymal, but not hematopoietic, RAGE has a central role in promoting AAI. In contrast to the lung, the absence of RAGE does not affect IL-33-induced ILC2 influx in the spleen, type 2 cytokine production in the peritoneum, or mucus hypersecretion in the gastrointestinal tract. CONCLUSIONS For the first time, this study demonstrates that a parenchymal factor, RAGE, mediates lung-specific accumulation of ILC2s.

Thrombospondin-1 triggers macrophage IL-10 production and promotes resolution of experimental lung injury.

Mononuclear phagocyte recognition of apoptotic cells triggering suppressive cytokine signaling is a key event in inflammation resolution from injury. Mice deficient in thrombospondin (TSP)-1 (thbs1−/−), an extracellular matrix glycoprotein that bridges cell–cell interactions, are prone to lipopolysaccharide-induced lung injury and show defective macrophage interleukin (IL)-10 production during the resolution phase of inflammation. Reconstitution of IL-10 rescues thbs1−/− mice from persistent neutrophilic lung inflammation and injury and thbs1−/− alveolar macrophages show defective IL-10 production following intratracheal instillation of apoptotic neutrophils despite intact efferocytosis. Following co-culture with apoptotic neutrophils, thbs1−/− macrophages show a selective defect in IL-10 production, whereas prostaglandin E2 and transforming growth factor beta 1 responses remain intact. Full macrophage IL-10 responses require the engagement of TSP-1 structural repeat 2 domain and the macrophage scavenger receptor CD36 LIMP-II Emp sequence homology (CLESH) domain in vitro. Although TSP-1 is not essential for macrophage engulfment of apoptotic neutrophils in vivo, TSP-1 aids in the curtailment of inflammatory responses during the resolution phase of injury in the lungs by providing a means by which apoptotic cells are recognized and trigger optimal IL-10 production by macrophages.

Prostaglandin E2 and IL‐23 plus IL‐1β Differentially Regulate the Th1/Th17 Immune Response of Human CD161+CD4+ Memory T Cells

Prostaglandin E2 (PGE2), interleukin (IL)‐23, and IL‐1beta (β) propagate inflammatory bowel disease (IBD) by enhancing the development and function of IL‐17 producing CD4+ T helper (Th17) cells. CD4+ T cells that express the C‐type lectin‐like receptor CD161 have been proposed to be the physiologic pool of circulating Th17 cells implicated in IBD. We sought to understand how PGE2, alone and in combination with IL‐23 and IL‐1β, modulate human peripheral CD161+CD4+ memory T cells. We found that CD161+ cells comprise a significant proportion of human peripheral CD4+ memory T cells. PGE2 and IL‐23 plus IL‐1β synergistically induced early IL‐17A secretion from CD161+CD4+ memory T cells and the selective enrichment of IL‐17A+CD161+CD4+ memory T cells in culture. Conversely, IL‐23 plus IL‐1β partially opposed the PGE2‐mediated repression of early interferon gamma (IFN‐γ) secretion from CD161+ cells, as well as the PGE2‐mediated depletion of IFN‐γ+CD161+ cells. Our results suggest that PGE2 and IL‐23 plus IL‐1β induce the Th17 immune response preferentially in CD161+CD4+ memory T cells, while divergently regulating their ability to express IFN‐γ. We hypothesize that Th17‐mediated chronic inflammation in IBD depends on the net response of CD161+CD4+ memory T cells to both PGE2 and IL‐23 plus IL‐1β. Clin Trans Sci 2011; Volume 4: 268–273

The mito-DAMP cardiolipin blocks IL-10 production causing persistent inflammation during bacterial pneumonia

Bacterial pneumonia is a significant healthcare burden worldwide. Failure to resolve inflammation after infection precipitates lung injury and an increase in morbidity and mortality. Gram-negative bacteria are common in pneumonia and increased levels of the mito-damage-associated molecular pattern (DAMP) cardiolipin can be detected in the lungs. Here we show that mice infected with Klebsiella pneumoniae develop lung injury with accumulation of cardiolipin. Cardiolipin inhibits resolution of inflammation by suppressing production of anti-inflammatory IL-10 by lung CD11b+Ly6GintLy6CloF4/80+ cells. Cardiolipin induces PPARγ SUMOylation, which causes recruitment of a repressive NCOR/HDAC3 complex to the IL-10 promoter, but not the TNF promoter, thereby tipping the balance towards inflammation rather than resolution. Inhibition of HDAC activity by sodium butyrate enhances recruitment of acetylated histone 3 to the IL-10 promoter and increases the concentration of IL-10 in the lungs. These findings identify a mechanism of persistent inflammation during pneumonia and indicate the potential of HDAC inhibition as a therapy.