Fig. 2.
Various immune and structural airway cells secrete inflammatory factors that promote the differentiation of naïve T cells into mature effector subtypes. These T cells further secrete subtype-dependent cytokines that bear the ability to promote and/or suppress the differentiation of disparate T cell subtypes. T helper 1 (TH1)- and TH2-derived IL-2, IL-4, IL-10, and IFN-γ inhibit the differentiation of naïve T cells into mature TH17 effector cells. Regulatory T (TREG) cells, depending on the concentration of their secreted cytokines, transforming growth factor-β1 (TGF-β1) and IL-10, can either promote or inhibit polarization toward a TH17 fate. Observations of such mechanisms, which ultimately alter airway function, underscore the complex immune signaling networks that regulate T cell differentiation and may in part explain the acquisition of mixed T cell endotypes in distinct individuals with asthma.