Cytokines (interleukin-9, IL-17, IL-22, IL-25 and IL-33) and asthma

Asthma is a reversible airway obstruction that is characterized by constriction of airway smooth muscle, hyper secretion of mucus, edema and airway hyper responsiveness (AHR), mucus secretion and thickening of the basement membrane underlying the airway epithelium. During the process of airway inflammation, complex interactions of innate and adaptive immune cells as well as structural cells and their cytokines have many important roles. It was believed that airway inflammation is orchestrated by allergen specific T helper (Th) 2 cells, which recruit and accumulate in the lungs and produce a range of different effector cytokines. However, more recent studies have revealed the potential collaboration of other helper T cells and their cytokines in this process. Th17 cell may have a role in severe asthma and chronic obstructive pulmonary disease (COPD). Interleukin (IL)-9-producing subset called Th9 cell, Th22 cells which primarily secrete IL-22, IL-13 and tumor necrosis factor-α and Th25 cells via producing IL-25 are believed to be important for initiating allergic reactions and developing airway inflammation. Cytokines are important in asthma and play a critical role in orchestrating the allergic inflammatory response, although the precise role of each cytokine remains to be determined. The aim of this review is to summarize the current knowledge about the possible roles of newly identified helper T cells derived cytokines (IL-9, 17, 22, 25 and IL-33) in asthma. The potential therapeutic applications emerging from the roles of these cytokines will be discussed as well.