The role of Th9 and other IL-9 producing cells in allergic asthma

Abstract

The incidence of allergic asthma has been increasing year by year. It is estimated that there are more than 300 million illnesses. It is associated with increased IgE, mast cell activation, airway hyperreactivity, excessive mucus production, and airway remodeling. The traditional view is that allergic asthma is associated with allergic reactions involving T helper type 2 (Th2) cells. Recent studies have found that different subsets of CD4+ T cells (Th17, Th9) as well as innately immunized cells such as mast cells and innate lymphocyte type 2 (ILC2s) are able to produce cytokine IL-9, leading to asthma. Th9 cells develop from nave T cells to IL-9 producing cells in the presence of IL-4 and TGF-β. IRF4, GATA3, a basic leucine zipper transcription factor, several transcription factors downstream of BATF and IL-4 such as signal transduction and STAT6-activated NFAT are activated. In addition, the transcription factor PU.1 downstream of TGF-β signaling appears to be also critical for the development of Th9 cells. IL-9 is a pleiotropic cytokine that affects the function of different target cells such as T cells, B cells, mast cells and airway epithelial cells by activating STAT1, STAT3 and STAT5. Due to its versatility, IL-9 has been shown to be involved in several diseases such as cancer, autoimmunity and other pathogenmediated immunomodulatory diseases. This article reviews the role of Th9 and IL-9producing cells in allergic asthma.