Robert W. Hallowell

Hyaluronan fragments induce IFNβ via a novel TLR4-TRIF-TBK1-IRF3-dependent pathway

BackgroundThe extracellular matrix plays a critical role in insuring tissue integrity and water homeostasis. However, breakdown products of the extracellular matrix have emerged as endogenous danger signals, designed to rapidly activate the immune system against a potential pathogen breach. Type I interferons play a critical role in the immune response against viral infections. In the lungs, hylauronan (HA) exists as a high molecular weight, biologically inert extracellular matrix component that is critical for maintaining lung function. When lung tissue is injured, HA is broken down into lower molecular weight fragments that alert the immune system to the breach in tissue integrity by activating innate immune responses. HA fragments are known to induce inflammatory gene expression via TLR-MyD88-dependent pathways.MethodsPrimary peritoneal macrophages from C57BL/6 wild type, TLR4 null, TLR3 null, MyD88 null, and TRIF null mice as well as alveolar and peritoneal macrophage cell lines were stimulated with HA fragments and cytokine production was assessed by rt-PCR and ELISA. Western blot analysis for IRF3 was preformed on cell lysates from macrophages stimulate with HA fragmentsResultsWe demonstrate for the first time that IFNβ is induced in murine macrophages by HA fragments. We also show that HA fragments induce IFNβ using a novel pathway independent of MyD88 but dependent on TLR4 via TRIF and IRF-3.ConclusionsOverall our findings reveal a novel signaling pathway by which hyaluronan can modulate inflammation and demonstrate the ability of hyaluronan fragments to induce the expression of type I interferons in response to tissue injury even in the absence of viral infection. This is independent of the pathway of the TLR2-MyD88 used by these matrix fragments to induce inflammatory chemokines. Thus, LMW HA may be modifying the inflammatory milieu simultaneously via several pathways.

Pulmonary manifestations of polymyositis/dermatomyositis.

The idiopathic inflammatory myopathies are a group of connective tissue diseases marked by varying degrees of muscle inflammation and clinical involvement of multiple organs, most notably, the lung. Pulmonary manifestations consist primarily of interstitial lung disease (ILD), which is associated with significant morbidity and mortality in myositis patients. Several myositis-specific antibodies have been discovered, as well as antibodies targeting various aminoacyl-tRNA synthetase enzymes. These antibodies are associated with various clinical features and a risk for developing ILD, and their presence carries a prognostic value in myositis patients. Steroids remain the first-line treatment for myositis-associated ILD and the antisynthetase syndrome, though other traditional immunosuppressants have demonstrated efficacy in numerous studies. While a majority of patients experience either stabilization or improvement in lung imaging and function, fatal progression is still reported in a significant number of cases. Further research is needed to develop more effective and targeted therapies.

Interstitial lung disease in patients with rheumatoid arthritis: spontaneous and drug induced.

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease characterized by the destruction of articular joint structures. RA is a systemic condition that often affects multiple organs, including the heart, lungs, and kidneys. Pulmonary complications of RA are relatively common and include pleural effusion, rheumatoid nodules, bronchiectasis, obliterative bronchiolitis, and opportunistic infections. Interstitial lung disease (ILD) is a common occurrence in patients with RA, and can range in severity from an asymptomatic incidental finding to a rapidly progressing life-threatening event. Usual interstitial pneumonia and non-specific interstitial pneumonia are the two most common patterns, though others have been reported. Various disease-modifying anti-rheumatic drugs—in particular, methotrexate and the tumor necrosis factor-alpha inhibitors—have been associated with RA-ILD in numerous case reports and case series, though it is often difficult to distinguish association from causality. Treatment for RA-ILD typically involves the use of high-dose corticosteroids, often in conjunction with alternative immunosuppressant agents such as azathioprine or mycophenolate mofetil, and outcomes vary widely depending on the initial pattern of lung disease. Additional research into the mechanisms driving RA-ILD is needed to guide future therapy.

Interstitial lung disease associated with the idiopathic inflammatory myopathies and the antisynthetase syndrome: Recent advances

Purpose of reviewTo highlight recent advances in understanding the clinical spectrum, pathogenesis, and treatment of interstitial lung disease associated with inflammatory myositis and the antisynthetase syndrome. Recent findingsIn recent years, serologic tests to identify the less common antisynthetase antibodies and the anti-MDA-5 antibody have become commercially available. As a result, several large, retrospective analyses have illustrated both the pulmonary and non-pulmonary features associated with the antisynthetase syndrome and myositis-related interstitial lung disease. Notably, there is now a better appreciation for the heterogeneity of these syndromes and the prognostic value in accurately identifying the associated autoantibodies. Human cytokine profiling and murine models of muscle inflammation suggest that tRNA synthetases themselves may act to trigger an initial innate immune response, thus offering new insights into the pathophysiology of these diseases. Finally, although randomized clinical trials in patients with myositis-associated interstitial lung disease have not occurred, new observational studies suggest that cyclosporine, tacrolimus, and rituximab may be effective treatment options. SummaryRecent research has provided a better understanding of the phenotype and prognosis that define interstitial lung disease in the setting of myositis and the antisynthetase syndrome. Although several therapeutic agents demonstrate promise, randomized trials are needed in order to establish the best clinical approach in these patients. Furthermore, additional research into the pathophysiology of this disease will be necessary to develop newer, more targeted therapeutics.

Pulmonary Vaccination as a Novel Treatment for Lung Fibrosis

Pulmonary fibrosis is an untreatable, uniformly fatal disease of unclear etiology that is the result of unremitting chronic inflammation. Recent studies have implicated bone marrow derived fibrocytes and M2 macrophages as playing key roles in propagating fibrosis. While the disease process is characterized by the accumulation of lymphocytes in the lung parenchyma and alveolar space, their role remains unclear. In this report we definitively demonstrate the ability of T cells to regulate lung inflammation leading to fibrosis. Specifically we demonstrate the ability of intranasal vaccinia vaccination to inhibit M2 macrophage generation and fibrocyte recruitment and hence the accumulation of collagen and death due to pulmonary failure. Mechanistically, we demonstrate the ability of lung Th1 cells to prevent fibrosis as vaccinia failed to prevent disease in Rag−/− mice or in mice in which the T cells lacked IFN-γ. Furthermore, vaccination 3 months prior to the initiation of fibrosis was able to mitigate the disease. Our findings clearly demonstrate the role of T cells in regulating pulmonary fibrosis as well as suggest that vaccinia-induced immunotherapy in the lung may prove to be a novel treatment approach to this otherwise fatal disease.

mTORC2 signalling regulates M2 macrophage differentiation in response to helminth infection and adaptive thermogenesis

Alternatively activated macrophages (M2) have an important function in innate immune responses to parasitic helminths, and emerging evidence also indicates these cells are regulators of systemic metabolism. Here we show a critical role for mTORC2 signalling in the generation of M2 macrophages. Abrogation of mTORC2 signalling in macrophages by selective conditional deletion of the adaptor molecule Rictor inhibits the generation of M2 macrophages while leaving the generation of classically activated macrophages (M1) intact. Selective deletion of Rictor in macrophages prevents M2 differentiation and clearance of a parasitic helminth infection in mice, and also abrogates the ability of mice to regulate brown fat and maintain core body temperature. Our findings define a role for mTORC2 in macrophages in integrating signals from the immune microenvironment to promote innate type 2 immunity, and also to integrate systemic metabolic and thermogenic responses.

Pulmonary delivery of docosahexaenoic acid mitigates bleomycin-induced pulmonary fibrosis.

BackgroundPulmonary fibrosis is an untreatable, fatal disease characterized by excess deposition of extracellular matrix and inflammation. Although the etiology of pulmonary fibrosis is unknown, recent studies have implicated dysregulated immune responses and wound healing. Since n-3 polyunsaturated fatty acids (n-3 PUFAs) may beneficially modulate immune responses in a variety of inflammatory disorders, we investigated the therapeutic role of docosahexaenoic acid (DHA), a single n-3 PUFA, in lung fibrosis.MethodsIntratracheal DHA or PBS was administered to mouse lungs 4 days prior to intratracheal bleomycin treatment. Body weight and survival were monitored for 21 days. Bronchoalveolar fluid (BALF) and lung inflammatory cells, cytokines, eicosanoids, histology and lung function were determined on serial days (0, 3, 7, 14, 21) after bleomycin injury.ResultsIntratracheal administration of DHA mitigated bleomycin-induced lung injury. Mice pretreated with DHA had significantly less weight loss and mortality after bleomycin injury. The lungs from DHA-pretreated mice had markedly less fibrosis. DHA pretreatment also protected the mice from the functional changes associated with bleomycin injury. Bleomycin-induced cellular inflammation in BALF and lung tissue was blunted by DHA pretreatment. These advantageous effects of DHA pretreatment were associated with decreased IL-6, LTB4, PGE2 and increased IL-10.ConclusionsOur findings demonstrate that intratracheal administration of DHA, a single PUFA, protected mice from the development of bleomycin-induced pulmonary inflammation and fibrosis. These results suggest that further investigations regarding the role of n-3 polyunsaturated fatty acids in fibrotic lung injury and repair are needed.

Severe pulmonary hypertension in idiopathic nonspecific interstitial pneumonia

Pulmonary hypertension (PH) is a common complication of interstitial lung disease (ILD), particularly in idiopathic pulmonary fibrosis (IPF) and ILD associated with connective tissue disease, where the underlying pathology is often a nonspecific interstitial pneumonia (NSIP) pattern. The degree of PH in ILD is typically mild to moderate and radiographic changes of ILD are usually prominent. We describe four patients with idiopathic NSIP and severe PH (mPAP > 40 mmHg). The average mean pulmonary artery pressure was 51±7 mmHg and pulmonary vascular resistance was 13±4 Woods units. Pulmonary function was characterized by mild restriction (total lung capacity 63–94% predicted) and profound reductions in DLCO (19–53% predicted). Computed tomographic imaging revealed minimal to moderate interstitial thickening without honeycombing. In two of the cases, an initial clinical diagnosis of idiopathic pulmonary arterial hypertension was made. Both were treated with intravenous epoprostenol, which was associated with worsening of hypoxemia. All four patients died or underwent lung transplant within 4 years of PH diagnonsis. Lung pathology in all four demonstrated fibrotic NSIP with medial thickening of the small and medium pulmonary arteries, and proliferative intimal lesions that stained negative for endothelial markers (CD31 and CD34) and positive for smooth muscle actin. There were no plexiform lesions. Severe pulmonary hypertension can therefore occur in idiopathic NSIP, even in the absence of advanced radiographic changes. Clinicians should suspect underlying ILD as the basis for PH when DLCO is severely reduced or gas exchange deteriorates with pulmonary vasodilator therapy.

Revisiting thalidomide: fighting with caution against idiopathic pulmonary fibrosis.

Thalidomide is an infamous drug whose use by pregnant women in the middle of last century tragically resulted in serious birth defects. However, as a result of its potent immunomodulatory, anti-inflammatory and antiangiogenic properties, thalidomide may be a potential therapy in many diseases. In recent years, thalidomide has been used effectively to treat various malignancies, including multiple myeloma, myelodysplastic syndromes, renal cell cancer, glioblastoma multiforme and prostate cancer. In addition, thalidomide has also proven effective against other immune-related diseases, including erythema nodosum leprosum and sarcoidosis. Idiopathic pulmonary fibrosis (IPF) is a deadly fibrotic disease with no effective treatment options. However, there is data to suggest that thalidomide may be useful in treating the chronic, disabling cough that accompanies IPF. It remains to be seen whether the immunomodulatory and antiangiogenic properties of thalidomide will also make it a potential therapy against the clinical progression of IPF.