Novel cytokines and cytokine-producing T cells in allergic disorders

Allergic diseases reflect various pathways of T lymphocyte inflammation and largely comprise T helper (Th) 2‐associated processes. Recent investigations have identified pathways involved in promoting Th2 responses. Additionally, novel T-cell subtypes, each with its own distinct cytokine profile, contribute to the heterogeneous presentations of allergic diseases. This article focuses on recent developments including novel effector (nuocytes, Th9, and Th22) and regulatory T-cell (Treg) families of lymphocytes as well as cytokines that are central in driving Th2 differentiation (interleukin [IL]-4, IL-9, IL-25, thymic stromal lymphopoietin [TSLP], and IL-33). Recent literature and investigations were reviewed. Unregulated IL-25, TSLP, and IL-33 activity results in activation of Th2 cells, mast cells, dendritic cells, eosinophils, and basophils, leading to inflammatory processes that define allergic disease. As such, these cytokines are central mediators capable of instigating the inflammatory processes responsible for allergen-mediated diseases. The previous paradigm of Th1/Th2 imbalance driving allergic disease is expanded by identification of novel T helper families (nuocytes, Th9, Th17, and Th22) with their signature cytokines, which provide alterative avenues for investigation of neutrophil-predominant asthma and other heterogeneous presentations of allergic diseases. IL-25, TSLP, and IL-33 are attractive targets for therapeutics designed to ameliorate Th2-mediated diseases such as allergic rhinitis and asthma. Moreover, the ability to delineate novel regulatory and effector T-cell lineages among CD4⁺ T cells challenges the Th1/Th2 paradigm of allergic disease and invites further avenues of investigation into the role of these cells in allergic disease.