Airway inflammation plays a critical role in the pathogenesis of chronic asthma. Glucocorticoids form the cornerstone of anti- inflammatory therapy in this disease. However, not all asthmatics improve their pulmonary function following glucocorticoid therapy. These patients are subjected to the unwanted side effects of prolonged systemic glucocorticoid therapy, often in situations where there is no evidence that it is exerting any appreciable benefit. The mechanisms for steroid resistance in these patients are poorly understood but may provide new insights into the basis of persistent airway inflammation in asthma. The present proposal will use cellular and molecular approaches to study the pathogenesis of steroid resistance (SR) vs steroid sensitive (SS) asthma. The central hypothesis which we will pursue is that a superantigen(s) triggers the selective expansion of IL-2 & IL-4 secreting Vbeta8+ T cells in SR asthma, the activation of which is sustained by persistent exposure to nominal peptide antigens presented by HLA-DR4+antigen-presenting cells (APC). Steroid resistance may be due to a combination of glucocorticoid receptor (GR) ligand and DNA binding defects which are cytokine- induced in the majority of patients. Taken together, persistent T cell activation and cytokine secretion results in enhanced mononuclear cell and eosinophil activation resistent to the anti- inflammatory effects of steroids.
Our specific aims are to analyze the T cell receptor (TCR) Vbeta gene usage of T cells and HLA haplotypes in SR asthma, (specific aim 1); to functionally characterize clonally expanded T cells in SR vs SS asthma (specific aim 2); to examine whether T cells and monocyte/macrophages from patients with SR, as compared to SS, asthma, have evidence for decreased GR binding to DNA recognition sites vs reduced GR ligand binding, and if so, to determine its functional significance (specific aim 3); determine the molecular basis for SR asthma by examining nuclear extracts of PBMC and BAL cells from SR asthmatics for evidence of increased expression of GR/beta, an endogenous inhibitor of GR DNA binding, or overexpression of transcription factors which interfere with GR ligand or DNA binding (Specific aim 4). The elucidation of mechanisms underlying steroid resistance will have important consequences for more objective criteria to diagnose steroid resistance, and the development of novel therapeutic modalities in the treatment of SR asthma as well as other chronic inflammatory conditions where altered glucocorticoid responsiveness contributes to persistent tissue inflammation.
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