Autoimmune Responses in Severe Asthma
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Asthma and autoimmune diseases both result from a dysregulated immune system, and have been conventionally considered to have mutually exclusive pathogenesis. Autoimmunity is believed to be an exaggerated Th1 response, while asthma with a Th2 underpinning is congruent with the well-accepted Th1/Th2 paradigm. The hypothesis of autoimmune involvement in asthma has received much recent interest, particularly in the adult late-onset non-atopic patients (the "intrinsic asthma"). Over the past decades, circulating autoantibodies against diverse self-targets (beta-2-adrenergic receptors, epithelial antigens, nuclear antigens, etc.) have been reported and subsequently dismissed to be epiphenomena resulting from a chronic inflammatory condition, primarily due to lack of evidence of causality/pathomechanism. Recent evidence of 'granulomas' in the lung biopsies of severe asthmatics, detection of pathogenic sputum autoantibodies against autologous eosinophil proteins (e.g., eosinophil peroxidase) and inadequate response to monoclonal antibody therapies (e.g., subcutaneous mepolizumab) in patients with evidence of airway autoantibodies suggest that the role of autoimmune mechanisms be revisited. In this review, we have gathered available reports of autoimmune responses in the lungs, reviewed the evidence in the context of immunogenic tissue-response and danger-associated molecular patterns, and constructed the possibility of an autoimmune-associated pathomechanism that may contribute to the severity of asthma.