IFN-γ production by innate immune cells is sufficient for development of hypersensitivity pneumonitis

Diagnosis of Fibrotic Hypersensitivity Pneumonitis: Is There a Role for Biomarkers?

Hypersensitivity pneumonitis is a complex interstitial lung syndrome and is associated with significant morbimortality, particularly for fibrotic disease. This condition is characterized by sensitization to a specific antigen, whose early identification is associated with improved outcomes. Biomarkers measure objectively biologic processes and may support clinical decisions. These tools evolved to play a crucial role in the diagnosis and management of a wide range of human diseases. This is not the case, however, with hypersensitivity pneumonitis, where there is still great room for research in the path to find consensual diagnostic biomarkers. Gaps in the current evidence include lack of validation, validation against healthy controls alone, small sampling and heterogeneity in diagnostic and classification criteria. Furthermore, discriminatory accuracy is currently limited by overlapping mechanisms of inflammation, damage and fibrogenesis between ILDs. Still, biomarkers such as BAL lymphocyte counts and specific serum IgGs made their way into clinical guidelines, while others including KL-6, SP-D, YKL-40 and apolipoproteins have shown promising results in leading centers and have potential to translate into daily practice. As research proceeds, it is expected that the emergence of novel categories of biomarkers will offer new and thriving tools that could complement those currently available.

ITK independent development of Th17 responses during hypersensitivity pneumonitis driven lung inflammation

T helper 17 (Th17) cells develop in response to T cell receptor signals (TCR) in the presence of specific environments, and produce the inflammatory cytokine IL17A. These cells have been implicated in a number of inflammatory diseases and represent a potential target for ameliorating such diseases. The kinase ITK, a critical regulator of TCR signals, has been shown to be required for the development of Th17 cells. However, we show here that lung inflammation induced by Saccharopolyspora rectivirgula (SR) induced Hypersensitivity pneumonitis (SR-HP) results in a neutrophil independent, and ITK independent Th17 responses, although ITK signals are required for γδ T cell production of IL17A. Transcriptomic analysis of resultant ITK independent Th17 cells suggest that the SR-HP-induced extrinsic inflammatory signals may override intrinsic T cell signals downstream of ITK to rescue Th17 responses in the absence of ITK. These findings suggest that the ability to pharmaceutically target ITK to suppress Th17 responses may be dependent on the type of inflammation.

Longstanding hypersensitivity pneumonitis and its response to roflumilast: A review of its likely immunological effects

We describe the case of a 42yr old man with evidence of hypersensitivity pneumonitis referred with cough and breathlessness for several years which had further deteriorated in the prior 12 months. He had known atopic asthma without evidence of activation.

A chest CT scan showed widespread ground glass change in his lung fields. He had feather bedding at home and in his youth cleaned aviaries. His forced vital capacity and lung volumes were reduced along with oxygen saturations at rest (92% on air), overnight (83% on air) and upon walking (78%). Steroids were commenced for a total of 6 months with little consistent improvement in symptoms or objective measures and with no change in his CT scan appearance. As a result, a trial of roflumilast (a phosphodiesterase-4 inhibitor) was commenced due to its range of immunological effects and in order to avoid long-term immune suppression with mycophenolate motefil in a young patient.

On roflumilast treatment his cough and breathlessness improved at 4 weeks and the chest crackles cleared. An interval Chest CT scan showed resolution of the ground glass change with improved CT scores that are maintained 2 yrs. All oxygen measures improved and nocturnal oxygen was discontinued. His Lung function has remained largely stable on roflumilast and symptoms of cough and breathlessness have resolved. This case report reviews the immunology of hypersensitivity pneumonitis and the likely actions of Roflumilast relevant to this condition. It is the first published case report documenting its use in hypersensitivity pneumonitis.

Lung Microenvironments and Disease Progression in Fibrotic Hypersensitivity Pneumonitis

Rationale: Fibrotic hypersensitivity pneumonitis (fHP) is an interstitial lung disease caused by sensitization to an inhaled allergen. Objectives: To identify the molecular determinants associated with progression of fibrosis. Methods: Nine fHP explant lungs and six unused donor lungs (as controls) were systematically sampled (4 samples/lung). According to microcomputed tomography measures, fHP cores were clustered into mild, moderate, and severe fibrosis groups. Gene expression profiles were assessed using weighted gene co-expression network analysis, xCell, gene ontology, and structure enrichment analysis. Gene expression of the prevailing molecular traits was also compared with idiopathic pulmonary fibrosis (IPF). The explant lung findings were evaluated in separate clinical fHP cohorts using tissue, BAL samples, and computed tomography scans. Measurements and Main Results: We found six molecular traits that associated with differential lung involvement. In fHP, extracellular matrix and antigen presentation/sensitization transcriptomic signatures characterized lung zones with only mild structural and histological changes, whereas signatures involved in honeycombing and B cells dominated the transcriptome in the most severely affected lung zones. With increasing disease severity, endothelial function was progressively lost, and progressive disruption in normal cellular homeostatic processes emerged. All six were also found in IPF, with largely similar associations with disease microenvironments. The molecular traits correlated with in vivo disease behavior in a separate clinical fHP cohort. Conclusions: We identified six molecular traits that characterize the morphological progression of fHP and associate with in vivo clinical behavior. Comparing IPF with fHP, the transcriptome landscape was determined considerably by local disease extent rather than by diagnosis alone.

Novel acute hypersensitivity pneumonitis model induced by airway mycosis and high dose lipopolysaccharide

BACKGROUND

Inhalation of fungal spores is a strong risk factor for severe asthma and experimentally leads to development of airway mycosis and asthma-like disease in mice. However, in addition to fungal spores, humans are simultaneously exposed to other inflammatory agents such as lipopolysaccharide (LPS), with uncertain relevance to disease expression. To determine how high dose inhalation of LPS influences the expression of allergic airway disease induced by the allergenic mold Aspergillus niger (A. niger).

METHODS

C57BL/6J mice were intranasally challenged with the viable spores of A. niger with and without 1 μg of LPS over two weeks. Changes in airway hyperreactivity, airway and lung inflammatory cell recruitment, antigen-specific immunoglobulins, and histopathology were determined.

RESULTS

In comparison to mice challenged only with A. niger, addition of LPS (1 μg) to A. niger abrogated airway hyperresponsiveness and strongly attenuated airway eosinophilia, PAS+ goblet cells and TH2 responses while enhancing TH1 and TH17 cell recruitment to lung. Addition of LPS resulted in more severe, diffuse lung inflammation with scattered, loosely-formed parenchymal granulomas, but failed to alter fungus-induced IgE and IgG antibodies.

CONCLUSIONS

In contrast to the strongly allergic lung phenotype induced by fungal spores alone, addition of a relatively high dose of LPS abrogates asthma-like features, replacing them with a phenotype more consistent with acute hypersensitivity pneumonitis (HP). These findings extend the already established link between airway mycosis and asthma to HP and describe a robust model for further dissecting the pathophysiology of HP.

Cytokine gene polymorphisms in Pigeon Breeder's Disease expression

BACKGROUND

Exaggerated immunological response to repeated inhalation of organic or chemical dusts may lead to Hypersensitivity Pneumonitis among sensitized individuals. Only a few exposed individuals became ill and disease expression pattern is highly variable which suggest that genetic factors may play a role.

AIM

To investigate interferon (IFN)-γ, tumour necrosis factor (TNF)-α, interleukin (IL)-6, transforming growth factor (TGF)-ß, and IL-10 gene polymorphisms in a cohort of pigeon breeder's disease (PBD) patients in comparison with exposed but healthy controls and the association with different patterns of disease.

METHODS

We evaluated 40 PBD patients and 70 exposed controls. IFN-γ, TNF-α, IL-6, TGF-ß, and IL-10 polymorphisms were determined by polymerase chain reaction-sequence specific primer amplification.

RESULTS

Polymorphism analysis of IFN-γ, TNF-α, IL-6, TGF-ß, and IL-10 genotypes and allele frequencies showed no differences between patients and controls. IFN-γ T/T genotype frequency was increased among patients with chronic presentation (RR=2.33, p=0.047) compared with those with acute/subacute presentation. Also, chronic presenting patients had an increased frequency of IFN-γ T allele (50% vs 22.5%, RR=1.76, p=0.011). No differences were found in TNF-α, IL-6, TGF-ß, and IL-10 genotypes neither allelic frequencies between both groups of patients. IL-6 C/C genotype was more frequent in patients who showed chronic evolution (RR=2.54, p=0.017), when comparing with patients with disease resolution.

CONCLUSION

IFN-γ T/T and the IL-6 C/C genotypes seem to play a role in HP expression due to avian exposure, as their frequencies are increased in chronic presentations or in those with chronic evolution one year after the initial diagnosis, respectively. (Sarcoidosis Vasc Diffuse Lung Dis 2020; 37 (3): e2020004).

Serum CXCL9 and CCL17 as biomarkers of declining pulmonary function in chronic bird-related hypersensitivity pneumonitis

The clinical course of chronic hypersensitivity pneumonitis (HP) with fibrosis is similar to that of idiopathic pulmonary fibrosis (IPF). Current research is expected to identify biomarkers effective in predicting the deterioration of lung function in a clinical setting. Our group analyzed the relationships between the following parameters in chronic bird-related HP: patient characteristics, serum markers, lung function, HRCT findings, BALF profiles, and the worsening of lung function. We also analyzed serum levels of CXCL9, CCL17, and Krebs von den Lungen 6 (KL-6) as serum markers. Patients showing declines in vital capacity (VC) of over 5% at 6 months after first admission were categorized as the “decline group”; the others were categorized as the “stable group.” The serum level of CCL17 and the percentage of BALF macrophages were significantly higher in the decline group compared to the stable group. Serum levels of CXCL9 and CCL17 were significant variables in a multivariate logistic regression analysis of factors associated with VC decline. Patients with a chemokine profile combining lower serum CXCL9 and higher serum CCL17 exhibited significantly larger VC decline in a cluster analysis. Higher serum CCL17 and lower serum CXCL9 were important predictors of worsening lung function in patients with chronic bird-related HP.

Early immunopathological events in acute model of mycobacterial hypersensitivity pneumonitis in mice

Prolonged exposure to antigens of non-tuberculous mycobacteria species colonizing industrial metalworking fluid (MWF), particularly Mycobacterium immunogenum (MI), has been implicated in chronic forms of hypersensitivity pneumonitis (HP) in machinists based on epidemiology studies and long-term exposure of mouse models. However, a role of short-term acute exposure to these antigens has not been described in the context of acute forms of HP. This study investigated short-term acute exposure of mice to MI cell lysate (or live cell suspension) via oropharyngeal aspiration. The results showed there was a dose- and time-dependent increase (peaking at 2 h post-instillation) in lung immunological responses in terms of the pro- (TNFα, IL-6, IL-1β) and anti-inflammatory (IL-10) cytokines. Bronchoalveolar lavage and histology showed neutrophils as the predominant infiltrating cell type, with lymphocytes <5% at all timepoints or concentrations. Granulomatous inflammation peaked between 8 and 24 h post-exposure, and resolved by 96 h. Live bacterial challenge, typically encountered in real-world exposures, showed no significant differences from bacterial lysate except for induction of appreciable levels of interferon (IFN)-γ, implying additional immunogenic potential. Collectively, the short-term mycobacterial challenge in mice led to a transient early immunopathologic response, with little adaptive immunity, which is consistent with events associated with human acute forms of HP. Screening of MWF-originated mycobacterial genotypes/variants (six of MI, four of M. chelonae, two of M. abscessus) showed both inter- and intra-species differences, with MI genotype MJY10 being the most immunogenic. In conclusion, this study characterized the first short-term mycobacterial exposure mouse model that mimics acute HP in machinists; this could serve as a potentially useful model for rapid screening of field MWF-associated mycobacteria for routine and timely occupational risk assessment and for investigating early biomarkers and mechanisms of this understudied immune lung disease.

Chronic hypersensitivity pneumonitis caused by Saccharopolyspora rectivirgula is not associated with a switch to a Th2 response

Hypersensitivity pneumonitis (HP) is an immune-mediated interstitial lung disease that develops following repeated exposure to inhaled environmental antigens. The disease results in alveolitis and granuloma formation and may progress to a chronic form associated with fibrosis; a greater understanding of the immunopathogenic mechanisms leading to chronic HP is needed. We used the Saccharopolyspora rectivirgula (SR) mouse model of HP to determine the extent to which a switch to a Th2-type immune response is associated with chronic HP. Exposure of wild-type (WT) and tlr2/9(-/-) mice to SR for 14 wk resulted in neutrophilic and lymphocytic alveolitis that was not dependent on Toll-like receptors (TLRs) 2 and 9. Long-term exposure of WT mice to SR resulted in a significant increase in collagen deposition, protein leakage, and IL-1α accompanied by a decrease in quasistatic compliance and total lung capacity compared with unexposed mice. This was associated with an increase in IL-17 but not IL-4 production or recruitment of Th2 cells. tlr2/9(-/-) mice exhibited an increase in protein leakage but less IL-1α and collagen deposition in the lungs compared with WT mice, yet they still displayed a decrease in quasistatic compliance, although total lung capacity was not affected. These mice exhibited an increase in both IL-13 and IL-17, which suggests that IL-13 may ameliorate some of the lung damage caused by long-term SR exposure. Our results suggest that lung pathology following long-term SR exposure in WT mice is associated with the IL-17 response and that TLRs 2 and 9 may inhibit the development of the IL-13/Th2 response.

Parallel Gene Expression Changes in Sarcoidosis Involving the Lacrimal Gland, Orbital Tissue, or Blood

IMPORTANCE

Sarcoidosis is a major cause of ocular or periocular inflammation. The pathogenesis of sarcoidosis is incompletely understood and diagnosis often requires a biopsy.

OBJECTIVE

To determine how gene expression in either orbital adipose tissue or the lacrimal gland affected by sarcoidosis compares with gene expression in other causes of orbital disease and how gene expression in tissue affected by sarcoidosis compares with gene expression in peripheral blood samples obtained from patients with sarcoidosis.

DESIGN, SETTING, AND PARTICIPANTS

In a multicenter, international, observational study, gene expression profiling of formalin-fixed biopsy specimens, using GeneChipp U133 Plus 2 microarrays (Affymetrix), was conducted between October 2012 and January 2014 on tissues biopsied from January 2000 through June 2013. Participants included 12 patients with orbital sarcoidosis (7 in adipose tissue; 5 affecting the lacrimal gland) as well as comparable tissue from 6 healthy individuals serving as controls or patients with thyroid eye disease, nonspecific orbital inflammation, or granulomatosis with polyangiitis. In addition, results were compared with gene expression in peripheral blood samples obtained from 12 historical individuals with sarcoidosis.

MAIN OUTCOMES AND MEASURES

Significantly differentially expressed transcripts defined as a minimum of a 1.5-fold increase or a comparable decrease and a false discovery rate of P < .05.

RESULTS

Signals from 2449 probe sets (transcripts from approximately 1522 genes) were significantly increased in the orbital adipose tissue from patients with sarcoidosis. Signals from 4050 probe sets (approximately 2619 genes) were significantly decreased. Signals from 3069 probe sets (approximately 2001 genes) were significantly higher and 3320 (approximately 2283 genes) were significantly lower in the lacrimal gland for patients with sarcoidosis. Ninety-two probe sets (approximately 69 genes) had significantly elevated signals and 67 probe sets (approximately 56 genes) had significantly lower signals in both orbital tissues and in peripheral blood from patients with sarcoidosis. The transcription factors, interferon-response factor 1, interferon-response factor 2, and nuclear factor κB, were strongly implicated in the expression of messenger RNA upregulated in common in the 3 tissues.

CONCLUSIONS AND RELEVANCE

Gene expression in sarcoidosis involving the orbit or lacrimal gland can be distinguished from gene expression patterns in control tissue and overlaps with many transcripts upregulated or downregulated in the peripheral blood of patients with sarcoidosis. These observations suggest that common pathogenic mechanisms contribute to sarcoidosis in different sites. The observations support the hypothesis that a pattern of gene expression profiles could provide diagnostic information in patients with sarcoidosis.

Interleukin-17A and Neutrophils in a Murine Model of Bird-Related Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is an immune mediated lung disease induced by the repeated inhalation of a wide variety of antigens. Bird-related hypersensitivity pneumonitis (BRHP) is one of the most common forms of HP in human and results from the inhalation of avian antigens. The findings of a recent clinical analysis suggest that in addition to Th1 factors, the levels of interleukin(IL)-17 and IL-17-associated transcripts are increased in the setting of HP, and that both IL-17A and neutrophils are crucial for the development of pulmonary inflammation in murine models of HP. Our objectives were to investigate the roles of IL-17A and neutrophils in granuloma-forming inflammation in an acute HP model. We developed a mouse model of acute BRHP using pigeon dropping extract. We evaluated the process of granuloma formation and the roles of both IL-17A and neutrophils in a model. We found that the neutralization of IL-17A by the antibody attenuated granuloma formation and the recruitment of neutrophils, and also decreased the expression level of chemokine(C-X-C motif) ligand 5 (CXCL5) in the acute HP model. We confirmed that most of the neutrophils in the acute HP model exhibited immunoreactivity to the anti-IL-17 antibody. We have identified the central roles of both IL-17A and neutrophils in the pathogenesis of granuloma formation in acute HP. We have also assumed that neutrophils are an important source of IL-17A in an acute HP model, and that the IL-17A-CXCL5 pathway may be responsible for the recruitment of neutrophils.

Mechanisms of interferon-γ production by neutrophils and its function during Streptococcus pneumoniae pneumonia

Bacterial pneumonia is a common public health problem associated with significant mortality, morbidity, and cost. Neutrophils are usually the earliest leukocytes to respond to bacteria in the lungs. Neutrophils rapidly sequester in the pulmonary microvasculature and migrate into the lung parenchyma and alveolar spaces, where they perform numerous effector functions for host defense. Previous studies showed that migrated neutrophils produce IFN-γ early during pneumonia induced by Streptococcus pneumoniae and that early production of IFN-γ regulates bacterial clearance. IFN-γ production by neutrophils requires Rac2, Hck/Lyn/Fgr Src family tyrosine kinases, and NADPH oxidase. Our current studies examined the mechanisms that regulate IFN-γ production by lung neutrophils during acute S. pneumoniae pneumonia in mice and its function. We demonstrate that IFN-γ production by neutrophils is a tightly regulated process that does not require IL-12. The adaptor molecule MyD88 is critical for IFN-γ production by neutrophils. The guanine nucleotide exchange factor CalDAG-GEFI modulates IFN-γ production. The CD11/CD18 complex, CD44, Toll-like receptors 2 and 4, TRIF, and Nrf2 are not required for IFN-γ production by neutrophils. The recently described neutrophil-dendritic cell hybrid cell, identified by its expression of Ly6G and CD11c, is present at low numbers in pneumonic lungs and is not a source of IFN-γ. IFN-γ produced by neutrophils early during acute S. pneumoniae pneumonia induces transcription of target genes in the lungs, which are critical for host defense. These studies underline the complexity of the neutrophil responses during pneumonia in the acute inflammatory response and in subsequent resolution or initiation of immune responses.

Age influence on hypersensitivity pneumonitis induced in mice by exposure to Pantoea agglomerans

Hypersensitivity pneumonitis (HP) represents the immunologically mediated lung disease induced by repeated inhalations of a wide variety of certain finely dispersed organic antigens. In susceptible subjects, these inhalations provoke a hypersensitivity reaction characterized by intense inflammation of the terminal bronchioles, the interstitium and the alveolar tree. The inflammation often organizes into granulomas and may progress to pulmonary fibrosis. Our previous work indicated that cell extract of gram-negative bacteria Pantoea agglomerans (SE-PA) causes, in young C57BL/6J mice, pulmonary changes that are very similar to the clinical manifestations of HP in men. The purpose of presented studies was to describe the response of mice immune system while exposed to SE-PA. Particular attention was paid to examine the age influence on SE-PA induced inflammation and fibrosis in lung tissue. We used 3- and 18-month-old C57BL/6J mice. Lung samples were collected from untreated mice and animals exposed to harmful agent for 7 and 28 days. HP development was monitored by histological and biochemical evaluation. Using ELISA tests, we examined concentration of pro- and anti-inflammatory cytokines in lung homogenates. Our study demonstrated again that SE-PA provokes in mice changes typical for the clinical picture of HP, and that successive stages of disease (acute, subacute and chronic) might be obtained by modulation of time exposure. Furthermore, we found that animals' age at the time of sensitization influences the nature of observed changes (cytokine expression pattern) and the final outcome (reaction intensity and scale of fibrosis).

TLR2 regulates neutrophil recruitment and cytokine production with minor contributions from TLR9 during hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is an interstitial lung disease that develops following repeated exposure to environmental antigens. The disease results in alveolitis, granuloma formation and may progress to a fibrotic chronic form, which is associated with significant morbidity and mortality. The severity of the disease correlates with a neutrophil rich influx and an IL-17 response. We used the Saccharopolysporarectivirgula (SR) model of HP to determine whether Toll-like receptors (TLR) 2 and 9 cooperate in neutrophil recruitment and IL-17-associated cytokine production during the development of HP. Stimulation of bone marrow derived macrophages (BMDMs) from C57BL/6, MyD88^-/- and TLR2/9^-/- mice with SR demonstrate that SR is a strong inducer of neutrophil chemokines and growth factors. The cytokines induced by SR were MyD88-dependent and, of those, most were partially or completely dependent on TLRs 2 and 9. Following in vivo exposure to SR, CXCL2 production and neutrophil recruitment were reduced in TLR2^-/- and TLR2/9^-/- mice suggesting that the response was largely dependent on TLR2; however the reduction was greatest in the TLR2/9^-/- double knockout mice indicating TLR9 may also contribute to the response. There was a reduction in the levels of pro-inflammatory cytokines TNFα and IL-6 as well as CCL3 and CCL4 in the BALF from TLR2/9^-/- mice compared to WT and single knockout (SKO) mice exposed one time to SR. The decrease in neutrophil recruitment and TNFα production in the TLR2/9^-/- mice was maintained throughout 3 weeks of SR exposures in comparison to WT and SKO mice. Both TLRs 2 and 9 contributed to the Th17 response; there was a decrease in Th17 cells and IL-17 mRNA in the TLR2/9^-/- mice in comparison to the WT and SKO mice. Despite the effects on neutrophil recruitment and the IL-17 response, TLR2/9^-/- mice developed granuloma formation similarly to WT and SKO mice suggesting that there are additional mediators and pattern recognition receptors involved in the disease.

Neutrophils infected with highly virulent influenza H3N2 virus exhibit augmented early cell death and rapid induction of type I interferon signaling pathways

We developed a model of influenza virus infection of neutrophils by inducing differentiation of the MPRO promyelocytic cell line. After 5 days of differentiation, about 20-30% of mature neutrophils could be detected. Only a fraction of neutrophils were infected by highly virulent influenza (HVI) virus, but were unable to support active viral replication compared with MDCK cells. HVI infection of neutrophils augmented early and late apoptosis as indicated by annexin V and TUNEL assays. Comparison between the global transcriptomic responses of neutrophils to HVI and low virulent influenza (LVI) revealed that the IFN regulatory factor and IFN signaling pathways were the most significantly overrepresented pathways, with activation of related genes in HVI as early as 3 h. Relatively consistent results were obtained by real-time RT-PCR of selected genes associated with the type I IFN pathway. Early after HVI infection, comparatively enhanced expression of apoptosis-related genes was also elicited.

Lactoferrin restrains allergen-induced pleurisy in mice

Objectives

The aim of this study was to assess the utility of lactoferrin (LF), a natural immunomodulator, to restrain allergen-induced pleurisy in mice.

Material and subjects

BALB/c female mice, 8- to 10-week old, weighing 24 g on average, were used.

Treatment

Mice were immunized intraperitoneally with 50 μg of ovalbumin (OVA) and the pleurisy was elicited 14 days later by intrapleural injection of 12.5 μg of OVA. LF was given 24 and 3 h before elicitation of the allergic reaction.

Methods

The cytokine levels in the pleural exudates were measured by immunoassays. The blood and pleural exudates smears were stained with Giemsa and May-Grünwald reagents and reviewed histologically. Lung sections were stained with eosin and hematoxylin for histological evaluation.

Results

Lactoferrin significantly decreased manifestation of pleurisy induced by OVA in a sensitized mouse model. In particular, the percentages of eosinophils in blood and pleural exudates were strongly diminished. The histological analysis of lungs revealed that LF diminished the development of pathological lesions, such as pulmonary edema, diffuse alveolar hemorrhage and hemosiderosis, which were found in the lungs after injection of the eliciting dose of OVA. LF also decreased the level of IL-5 secreted into the pleural fluid.

Conclusions

This is a first demonstration that LF significantly decreases antigen-specific pleurisy in a sensitized mouse model.

Toll like receptors in diseases of the lung

The lung is in continuous contact with a diverse array of infectious agents, foreign antigens, and host-derived danger signals. To sample this expansive internal and external milieu, both resident myeloid and stromal/structure cells of the lung express a full complement of toll like receptors (TLRs) which recognize pathogen-associated molecular patterns (PAMPs) and endogenous danger-associated molecular patterns (DAMPs). TLRs play a vital role in immune host defense against bacterial, mycobacterial, fungal, and viral pathogens of the lung. Additionally, TLRs contribute to disease pathogenesis in non-infectious pulmonary disorders, including airway disease, acute lung injury, and interstitial lung disease. In this review, TLR biology in the context of experimental infectious and non-infectious lung disease is discussed, and correlates to human lung disease, including therapeutic implications of these findings, are defined.

T-bet controls severity of hypersensitivity pneumonitis

Hypersensitivity Pneumonitis (HP) is an interstitial lung disease that develops following repeated exposure to inhaled environmental antigens. The disease is characterized by alveolitis, granuloma formation and in some patients' fibrosis. IFNγ plays a critical role in HP; in the absence of IFNγ granuloma formation does not occur. However, recent studies using animal models of HP have suggested that HP is a Th17 disease calling into question the role of IFNγ. In this study, we report that initially IFNγ production is dependent on IL-18 and the transcription factor T-bet, however as the disease continues IFNγ production is IL-18-independent and partially T-bet dependent. Although IFNγ production is required for granuloma formation its role is distinct from that of T-bet. Mice that are deficient in T-bet and exposed to S. rectivirgula develop more severe disease characterized by an exacerbated Th17 cell response, decreased Th1 cell response, and increased collagen production in the lung. T-bet-mediated protection does not appear to be due to the development of a protective Th1 response; shifting the balance from a Th17 predominant response to a Th1 response by inhibition of IL-6 also results in lung pathology. The results from this study suggest that both Th1 and Th17 cells can be pathogenic in this model and that IFNγ and T-bet play divergent roles in the disease process.

Interferon-γ production by neutrophils during bacterial pneumonia in mice

RATIONALE

Neutrophils are usually the first circulating leukocytes to respond during bacterial pneumonia. Their expression of oxidants, proteases, and other mediators present in granules is well documented, but their ability to produce mediators through transcription and translation after migration to an inflammatory site has been appreciated only more recently. Interferon (IFN)-γ is a cytokine with many functions important in host defense and immunity.

OBJECTIVES

To examine the expression and function of IFN-γ in bacterial pneumonias.

METHODS

IFN-γ mRNA and protein were measured in digests of mouse lungs with 24-hour bacterial pneumonia. Bacterial clearance was studied with IFN-γ-deficient mice.

MEASUREMENTS AND MAIN RESULTS

Streptococcus pneumoniae and Staphylococcus aureus each induce expression of IFN-γ mRNA and protein by neutrophils by 24 hours. Only neutrophils that have migrated into pneumonic tissue produce IFN-γ. Deficiency of Hck/Fgr/Lyn, Rac2, or gp91(phox) prevents IFN-γ production. IFN-γ enhances bacterial clearance and is required for formation of neutrophil extracellular traps. In contrast, Pseudomonas aeruginosa and Escherichia coli induce production of IFN-γ mRNA but not protein. During pneumonia induced by E. coli but not S. pneumoniae, neutrophils produce microRNAs that target the 3' untranslated region of the IFN-γ gene.

CONCLUSIONS

S. pneumoniae and S. aureus, but not P. aeruginosa and E. coli, induce emigrated neutrophils to produce IFN-γ within 24 hours. Hck/Fgr/Lyn, Rac2, and NADPH oxidase are required for IFN-γ production. IFN-γ facilitates bacterial clearance at least in part through regulating formation of neutrophil extracellular traps. Differential expression by neutrophils of microRNAs that target the 3' untranslated region of the IFN-γ gene may contribute to the pathogen-specific regulation of translation.

Galectin-9 expands immunosuppressive macrophages to ameliorate T-cell-mediated lung inflammation

Galectin-9 (Gal-9) plays pivotal roles in the modulation of innate and adaptive immunity to suppress T-cell-mediated autoimmune models. However, it remains unclear if Gal-9 plays a suppressive role for T-cell function in non-autoimmune disease models. We assessed the effects of Gal-9 on experimental hypersensitivity pneumonitis induced by Trichosporon asahii. When Gal-9 was given subcutaneously to C57BL/6 mice at the time of challenge with T. asahii, it significantly suppressed T. asahii-induced lung inflammation, as the levels of IL-1, IL-6, IFN-gamma, and IL-17 were significantly reduced in the BALF of Gal-9-treated mice. Moreover, co-culture of anti-CD3-stimulated CD4 T cells with BALF cells harvested from Gal-9-treated mice on day 1 resulted in diminished CD4 T-cell proliferation and decreased levels of IFN-gamma and IL-17. CD11b(+)Ly-6C(high)F4/80(+) BALF Mphi expanded by Gal-9 were responsible for the suppression. We further found in vitro that Gal-9, only in the presence of T. asahii, expands CD11b(+)Ly-6C(high)F4/80(+) cells from BM cells, and the cells suppress T-cell proliferation and IFN-gamma and IL-17 production. The present results indicate that Gal-9 expands immunosuppressive CD11b(+)Ly-6C(high) Mphi to ameliorate Th1/Th17 cell-mediated hypersensitivity pneumonitis.

Fcgamma receptors modulate pulmonary inflammation by activating innate immune cells in murine hypersensitivity pneumonitis

Background

Hypersensitivity pneumonitis (HP) is an interstitial lung disease that develops following repeated exposure to inhaled particulate antigens. The family of Fcγ receptors (FcγRs) has emerged as central regulators for modulating both pro-and anti-inflammatory responses. However, the role of FcγRs in the development of HP has not been investigated yet.

Methods

To explore the functional roles of FcγRs in HP, FcγR^-/- and B6 mice were challenged with Saccharopolyspora rectivirgula (SR) antigen intranasally, and compared these mice in terms of the histological change, infiltrated immune cells in BALF and in vitro immune responses.

Results

FcγR^-/- mice exhibited attenuation of HP in terms of histological alterations, and reduced numbers of neutrophils and macrophages in and the increased CD4:CD8 ratio of bronchoalveolar lavage fluid. The lungs of FcγR^-/- mice showed high production of Th2 cytokine such as IL-4 and slightly low production of Th1 cytokine, INF-γ compared to those of B6 mice. However, SR-specific adaptive immune responses of FcγR^-/- mice were similar to those of B6 mice.

Conclusion

These results demonstrate that activating Fcγ receptors play an important role in activating neutrophils and macrophages in pulmonary inflammation and inducing Th1 differentiation by regulating cytokine expression in SR-induced HP.

Protein kinase D1 is essential for the proinflammatory response induced by hypersensitivity pneumonitis-causing thermophilic actinomycetes Saccharopolyspora rectivirgula

Hypersensitivity pneumonitis is an interstitial lung disease that results from repeated pulmonary exposure to various organic Ags, including Saccharopolyspora rectivirgula, the causative agent of farmer's lung disease. Although the contributions of proinflammatory mediators to the disease pathogenesis are relatively well documented, the mechanism(s) involved in the initiation of proinflammatory responses against the causative microorganisms and the contribution of signaling molecules involved in the host immune defense have not been fully elucidated. In the current study, we found that S. rectivirgula induces the activation of protein kinase D (PKD)1 in lung cells in vitro and in vivo. Activation of PKD1 by S. rectivirgula was dependent on MyD88. Inhibition of PKD by pharmacological PKD inhibitor Gö6976 and silencing of PKD1 expression by small interfering RNA revealed that PKD1 is indispensable for S. rectivirgula-mediated activation of MAPKs and NF-kappaB and the expression of various proinflammatory cytokines and chemokines. In addition, compared with controls, mice pretreated with Gö6976 showed significantly suppressed alveolitis and neutrophil influx in bronchial alveolar lavage fluid and interstitial lung tissue, as well as substantially decreased myeloperoxidase activity in the lung after pulmonary exposure to S. rectivirgula. These results demonstrate that PKD1 is essential for S. rectivirgula-mediated proinflammatory immune responses and neutrophil influx in the lung. Our findings also imply the possibility that PKD1 is one of the critical factors that play a regulatory role in the development of hypersensitivity pneumonitis caused by microbial Ags and that inhibition of PKD1 activation could be an effective way to control microbial Ag-induced hypersensitivity pneumonitis.

Toll-like receptor 6 drives interleukin-17A expression during experimental hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is a T-cell-driven disease that is histologically characterized by diffuse mononuclear cell infiltrates and loosely formed granulomas in the lungs. We have previously reported that interleukin-17A (IL-17A) contributes to the development of experimental HP, and that the pattern recognition receptor Toll-like receptor 6 (TLR6) might be a factor in the initiation of this response. Using a well-established murine model of Saccharopolyspora rectivirgula-induced HP, we investigated the role of TLR6 in the immunopathogenesis of this disease. In the absence of TLR6 signalling, mice that received multiple challenges with S. rectivirgula-antigen (SR-Ag) had significantly less lung inflammation compared with C57BL/6 mice (wild-type; WT) similarly challenged with SR-Ag. Flow cytometric analysis of whole lung samples from SR-Ag-challenged mice showed that TLR6(-/-) mice had a decreased CD4(+) : CD8(+) T-cell ratio compared with WT mice. Cytokine analysis at various days after the final SR-Ag challenge revealed that whole lungs from TLR6(-/-) mice contained significantly less IL-17A than lungs from WT mice with HP. The IL-17A-driving cytokines IL-21 and IL-23 were also expressed at lower levels in SR-Ag-challenged TLR6(-/-) mice, when compared with SR-Ag-challenged WT mice. Other pro-inflammatory cytokines, namely interferon-gamma and RANTES, were also found to be regulated by TLR6 signalling. Anti-TLR6 neutralizing antibody treatment of dispersed lung cells significantly impaired SR-Ag-induced IL-17A and IL-6 generation. Together, these results indicate that TLR6 plays a pivotal role in the development and severity of HP via its role in IL-17A production.

CD4(+)CD25(+) regulatory T cells attenuate Hypersensitivity Pneumonitis by suppressing IFN-gamma production by CD4(+) and CD8(+) T cells

HP results from the repeated inhalation of environmental antigens; however, the roles of CD4(+)CD25(+) T(reg) cells in HP are unknown. Therefore, we investigated the functions of CD4(+)CD25(+) T(reg) cells in SR-induced murine HP. More severe HP was observed in CD4(+)CD25(+) T(reg) cell-depleted mice than in control mice in terms of histological alterations, inflammatory cell numbers in BALF, and the serum level of SR-specific IgG, which were restored by the adoptive transfer of CD4(+)CD25(+) T(reg) cells. The CD4(+)CD25(+) T(reg) cell-depleted mice also showed elevated levels of IFN-gamma, TGF-beta, and reduced IL-4 production in the lungs. Moreover, IL-10 production of CD4(+)CD25(+) T(reg) cells and direct contact between CD4(+)CD25(+) T(reg) cells and CD4(+) or CD8(+) T cells in BALF resulted in reduced IFN-gamma production. Taken together, CD4(+)CD25(+) T(reg) cells play a protective role in SR-induced HP by suppressing IFN-gamma production by T cells.

Interleukin 12, interleukin 18, and tumor necrosis factor alpha release by alveolar macrophages: acute and chronic hypersensitivity pneumonitis

BACKGROUND

Hypersensitivity pneumonitis (HP) is characterized by a granulomatous inflammation and may show various forms of clinical presentation, such as the acute, subacute, and chronic forms. The TH1-associated cytokines interleukin (IL) 12 and IL-18 and tumor necrosis factor alpha (TNF-alpha) may be involved in the pathogenesis of both the acute and chronic forms of HP.

OBJECTIVE

To compare the release of IL-12, IL-18, and TNF-alpha from bronchoalveolar lavage (BAL) macrophages in these 2 forms of HP.

METHODS

Patients underwent BAL 0 to 6 days after the last antigen exposure. Alveolar macrophages (AMs) from BAL in 6 patients with acute HP, 16 with chronic HP, and 11 controls were cultured for 24 hours. Cytokines in the culture supernatants were measured by enzyme-linked immunosorbent assay.

RESULTS

The production of IL-12, IL-18, and TNF-alpha by AMs was increased in patients with both acute and chronic forms in either the absence or presence of lipopolysaccharide compared with controls. The levels of IL-12, IL-18, and TNF-alpha showed no difference between patients with acute and chronic HP. The spontaneous production of IL-12, IL-18, and TNF-alpha did not correlate with the CD4/CD8 ratio in BAL. The spontaneous and lipopolysaccharide-stimulated release of IL-12 showed a positive correlation with the percentage of lymphocytes (r = .470, P = .03; r = .496, P = .02; respectively) in BAL.

CONCLUSIONS

This study demonstrates that an increased release of IL-12, IL-18, and TNF-alpha by AMs is associated with both the acute and chronic forms of HP.

Hypersensitivity pneumonitis

The first few cases of hypersensitivity pneumonitis (HP) were described in the early 20th century in farmers exposed to moldy hay or straw. As then, HP has been ascribed to multiple inhaled antigens found in a large variety of environmental settings. Hypersensitivity pneumonitis results from an exaggerated immune response, which gives rise to acute infection-like symptoms or to progressive, sometimes irreversible lung damage. The diagnosis is based on a combination of clinical characteristics of the disease. Clinical diagnostic criteria have recently been published. The immune mechanisms leading to HP are still incompletely understood. Initially, believed to be a classes III and IV immune response, we now have a clearer understanding of the complex inflammatory events involved. These include the release of pro inflammatory cytokines and a decrease in the immune control mechanisms via surfactant, dendritic and T-regulatory cells. Despite the improved understanding, the treatment and outcome of HP have not changed. Oral corticosteroids remain the only effective drugs and contact withdrawal constitutes the ideal solution. If unchecked, HP can lead to irreversible lung damage in the form of fibrosis or emphysema, respiratory insufficiency and even death.

Interleukin-17-mediated immunopathogenesis in experimental hypersensitivity pneumonitis

RATIONALE

T cells play a critical role in the development of Saccharopolyspora rectivirgula-induced hypersensitivity pneumonitis (HP) but little is known about the role of IL-17A in this disease.

OBJECTIVES

We examined the role of IL-17A in a murine model of S. rectivirgula antigen (SR-Ag)-induced HP.

METHODS

Experimental HP was induced by oropharyngeal instillation of SR-Ag in wild-type and IL-17 gene-deficient mice.

MEASUREMENTS AND MAIN RESULTS

SR-Ag-induced murine HP was characterized by increased transcript levels of IFN-gamma and IL-12p35 compared with saline-treated control mice. Furthermore, mice with HP showed increased IL-17 in lung homogenates, bronchoalveolar lavage fluid, and ex-vivo lung cultures compared with control mice. Flow cytometric analysis of SR-Ag-challenged lungs revealed increased Th17 and CD11c(+) cells. The role of IL-17 in SR-induced HP was examined in IL-17 deficient (IL17(-/-)) and in wild-type (IL-17(+/+)) mice immunodepleted of IL-17. Histological examination of IL17(-/-) mice challenged with SR-Ag revealed reduced inflammatory cell infiltration, decreased CD11c(+) cells, and reduced levels of inflammatory mediators such as IL-12p70, CCL3, and CXCL9 compared with similarly treated IL17(+/+) mice. Anti-IL-17 antibody treatment of IL-17(+/+) mice with HP resulted in reduced inflammation and a lower percentage of CD11c(+) cells compared with IgG-treated IL-17(+/+) mice with HP.

CONCLUSIONS

SR-Ag-induced IL-17 plays a pivotal role in the immunopathology of HP and targeting IL-17 is an attractive therapeutic option for this disease.

Where asthma and hypersensitivity pneumonitis meet and differ: noneosinophilic severe asthma

Asthma is a type-I allergic airway disease characterized by Th(2) cells and IgE. Episodes of bronchial inflammation, eosinophilic in nature and promoting bronchoconstriction, may become chronic and lead to persistent respiratory symptoms and irreversible structural airway changes. Representative mostly of mild to moderate asthma, this clinical definition fails to account for the atypical and often more severe phenotype found in a considerable proportion of asthmatics who have increased neutrophil cell counts in the airways as a distinguishing trait. Neutrophilic inflammation is a hallmark of another type of allergic airway pathology, hypersensitivity pneumonitis. Considered as an immune counterpart of asthma, hypersensitivity pneumonitis is a prototypical type-III allergic inflammatory reaction involving the alveoli and lung interstitium, steered by Th(1) cells and IgG and, in its chronic form, accompanied by fibrosis. Although pathologically very different and commonly approached as separate disorders, as discussed in this review, clinical studies as well as data from animal models reveal undeniable parallels between both airway diseases. Danger signaling elicited by the allergenic agent or by accompanying microbial patterns emerges as critical in enabling immune sensitization and in determining the type of sensitization and ensuing allergic disease. On this basis, we propose that asthma allergens cause severe noneosinophilic asthma because of sensitization in the presence of hypersensitivity pneumonitis-promoting danger signaling.

Radiation-induced IFN-gamma production within the tumor microenvironment influences antitumor immunity

Alterations to the tumor microenvironment following localized irradiation may influence the effectiveness of subsequent immunotherapy. The objective of this study was to determine how IFN-gamma influences the inflammatory response within this dynamic environment following radiotherapy. B16/OVA melanoma cells were implanted into C57BL/6 (wild-type (WT)) and IFN-gamma-deficient (IFN-gamma-/-) mice. Seven days after implantation, mice received 15 Gy of localized tumor irradiation and were assessed 7 days later. Irradiation up-regulated the expression of VCAM-1 on the vasculature of tumors grown in WT but not in IFN-gamma-/- mice. Levels of the IFN-gamma-inducible chemokines MIG and IFN-gamma-inducible protein 10 were decreased in irradiated tumors from IFN-gamma-/- mice compared with WT. In addition to inducing molecular cues necessary for T cell infiltration, surface MHC class I expression is also up-regulated in response to IFN-gamma produced after irradiation. The role of IFN-gamma signaling in tumor cells on class I expression was tested using B16/OVA cells engineered to overexpress a dominant negative mutant IFN-gamma receptor (B16/OVA/DNM). Following implantation and treatment, expression of surface class I on tumor cells in vivo was increased in B16/OVA, but not in B16/OVA/DNM tumors, suggesting IFN-gamma acts directly on tumor cells to induce class I up-regulation. These increases in MHC class I expression correlated with greater levels of activated STAT1. Thus, IFN-gamma is instrumental in creating a tumor microenvironment conducive for T cell infiltration and tumor cell target recognition.

CD4-expressing cells are early mediators of the innate immune system during sepsis

It is well established that the immune response to sepsis is mediated by leukocytes associated with the innate immune system. However, there is an emerging view that T lymphocytes can also mediate this response. Here, we observed a significant depletion of both CD4 and CD8 T cells in human patients after blunt trauma. To determine what effect the loss of these cells may have during a subsequent infection, we obtained CD4- and CD8-deficient mice and subjected them to cecal ligation and puncture (CLP). We observed that CD4 knockout (KO) mice showed increased CLP-induced mortality compared with CD8-deficient and wild-type (WT) mice especially within the first 30 h of injury. CD4 KO mice also exhibited significantly increased IL-6 concentrations after the CLP. The CD4 KO mice had an increased concentration of bacteremia as compared with WT mice. Antibiotic treatment decreased mortality in the CD4 KO mice as compared with no changes in the wild mice after CLP. Neutrophils isolated from septic CD4 KO mice showed decreased spontaneous oxidative burst compared with neutrophils taken from septic controls. We examined the role of IFN-gamma by using mice deficient in this cytokine and found these mice to have significantly higher mortality as compared with WT mice. Finally, we detected a 2-fold increase in CD11b+ cells that exhibited intracellular IFN-gamma staining in the peritoneum of WT mice after CLP. The data suggest that CD4+ cells may facilitate the early clearance of bacteria by regulating neutrophils function possibly through an IFN-gamma-dependent mechanism.

MyD88 is necessary for neutrophil recruitment in hypersensitivity pneumonitis

Hypersensitivity pneumonitis is an interstitial lung disease that is characterized by alveolitis, granuloma formation, and in some patients, fibrosis. Using the Saccharopolyspora rectivirgula animal model of Farmer's lung disease, our laboratory has demonstrated that neutrophils play a critical role in IFN-gamma production during the acute phase of the disease. As IFN-gamma is necessary for granuloma formation, it is important to identify the factors that lead to neutrophil recruitment during disease. To begin to identify the pattern recognition receptors (PRRs) that initiate chemokine production, leading to neutrophil recruitment following S. rectivirgula exposure, we examined the role of MyD88 and TLR2. Our results demonstrate that neutrophil recruitment, as measured by flow cytometry and the myeloperoxidase assay, was abolished in the absence of MyD88 following S. rectivirgula exposure. The decrease in neutrophil recruitment was likely a result of a significant decrease in production of neutrophil chemokines MIP-2 and keratinocyte-derived chemokine. These results suggest that S. rectivirgula interacts with PRRs that are upstream of the MyD88 pathway to initiate cytokine and chemokine production. In vitro studies suggest that S. rectivirgula can interact with TLR2, and stimulation of adherent cells from TLR2 knockout (KO) mice with S. rectivirgula resulted in a significant decrease in MIP-2 production. However, TLR2 KO mice did not have a reduction in neutrophil recruitment compared with wild-type mice following S. rectivirgula exposure. The results from our studies suggest that one or more PRR(s) upstream of MyD88 are necessary for neutrophil recruitment following S. rectivirgula exposure.

Overexpression of GATA-3 Protects against the Development of Hypersensitivity Pneumonitis

RATIONALE

Hypersensitivity pneumonitis (HP) is mediated by a Th1 immune response. Transcription factor GATA binding protein-3 (GATA-3) is believed to be a key regulator of Th2 differentiation and thus might play regulatory roles in the pathogenesis of hypersensitivity pneumonitis (HP).

OBJECTIVES

We examined the effect of GATA-3 overexpression on the development of HP in mice.

METHODS

Wild-type C57BL/6 mice and GATA-3-overexpressing mice of the same background were used in this study. HP was induced by repeated exposure to Saccharopolyspora rectivirgula, the causative antigen of farmer's lung.

MEASUREMENTS AND MAIN RESULTS

Antigen exposure resulted in a marked inflammatory response with enhanced pulmonary expression of T-bet and the Th1 cytokine interferon (IFN)-gamma in wild-type mice. The degree of pulmonary inflammation was much less severe in GATA-3-overexpressing mice. The induction of T-bet and IFN-gamma genes was suppressed, but a significant induction of Th2 cytokines, including IL-5 and IL-13, was observed in the lungs of GATA-3-overexpressing mice after antigen exposure. Supplementation with recombinant IFN-gamma enhanced lung inflammatory responses in GATA-3-overexpressing mice to the level of wild-type mice. Because antigen-induced IFN-gamma production predominantly occurred in CD4+ T cells, nude mice were transferred with CD4+ T cells from either wild-type or GATA-3-overexpressing mice and subsequently exposed to antigen. Lung inflammatory responses were significantly lower in nude mice transferred with CD4+ T cells from GATA-3-overexpressing mice than in those with wild-type CD4+ T cells, with a reduction of lung IFN-gamma level.

CONCLUSIONS

These results indicate that overexpression of GATA-3 attenuates the development of HP by correcting the Th1-polarizing condition.

IL-4-Secreting NKT Cells Prevent Hypersensitivity Pneumonitis by Suppressing IFN-γ-Producing Neutrophils

Hypersensitivity pneumonitis (HP) is mediated by Th1 immune response. NKT cells regulate immune responses by modulating the Th1/Th2 balance. Therefore, we postulated that NKT cells play a critical role in the development of the HP by modulating the Th1/Th2 response. To address this issue, we explored the functional roles of NKT cells in Saccharopolyspora rectivirgula (SR)-induced HP. In CD1d(-/-) mice, the HP was worse in terms of histological changes, hydroxyproline levels, the CD4:CD8 ratio in bronchoalveolar lavage fluid, and SR-specific immune responses than in control mice. CD1d(-/-) mice showed elevated IFN-gamma production in the lung during the HP, and this was produced mainly by Gr-1+ neutrophils. The blockade of IFN-gamma in CD1d(-/-) mice attenuated the HP, whereas the injection of rIFN-gamma aggravated it. Moreover, the depletion of Gr-1+ neutrophils reduced CD8+ T cell numbers in bronchoalveolar lavage fluid during the HP. The adoptive transfer of IL-4(-/-) mouse NKT cells did not attenuate the HP, whereas wild-type or IFN-gamma(-/-) mouse NKT cells suppressed the HP. In conclusion, NKT cells producing IL-4 play a protective role in SR-induced HP by suppressing IFN-gamma-producing neutrophils, which induce the activation and proliferation of CD8+ T cells in the lung.

Engagement of glucocorticoid-induced TNF receptor costimulates NKT cell activation in vitro and in vivo

Glucocorticoid-induced TNF receptor (GITR) is known to provide costimulatory signals to CD4+CD25- and CD4+CD25+ T cells during immune responses in vivo. However, the functional roles of GITR expressed on NKT cells have not been well characterized. In this study, we have explored the functions of GITR as a costimulatory factor on NKT cells. GITR was found to be constitutively expressed on NKT cells and its expression was enhanced by TCR signals. GITR engagement using DTA-1, an agonistic mAb against GITR, in the presence of TCR signals, augmented IL-2 production, the expression of activation markers, cell cycle progression, and the nuclear translocations of NF-kappaB p50 and p65. Furthermore, GITR engagement enhanced the production of IL-4, IL-10, IL-13, and IFN-gamma by NKT cells and the expression level of phosphorylated p65 in NKT cells in the presence of TCR engagement, indicating that GITR provides costimulatory signals to NKT cells. The costimulatory effects of GITR on NKT cells were comparable to those of CD28 in terms of cytokine production. Moreover, the coinjection of DTA-1 and alpha-galactosylceramide into B6 mice induced more IL-4 and IFN-gamma production than the coinjection of control mAbs and alpha-galactosylceramide. In addition, the adoptive transfer of DTA-1-pretreated NKT cells into CD1d(-/-) mice attenuated hypersensitivity pneumonitis more than control IgG pretreated NKT cells in these mice. These findings demonstrate that GITR engagement on NKT cells modulates immune responses in hypersensitivity pneumonitis in vivo. Taken together, our findings suggest that GITR engagement costimulates NKT cells and contributes to the regulation of immune-associated disease processes in vivo.