Allergies - A T cells perspective in the era beyond the TH1/TH2 paradigm

•Review of the role of (novel) T cell subsets in the pathogenesis of allergies•Focus on pathogenesis of atopic dermatitis, asthma and allergic rhinitis•T cell induction, regulation, effector phase and plasticity in allergic diseases•Recent discoveries in the field of T cell plasticity summarized

Allergic diseases have emerged as a major health care burden, especially in the western hemisphere. They are defined by overshooting reactions of an aberrant immune system to harmless exogenous stimuli. The TH1/TH2 paradigm assumes that a dominance of TH2 cell activation and an inadequate TH1 cell response are responsible for the development of allergies. However, the characterization of additional T helper cell subpopulations such as TH9, TH17, TH22, THGM-CSF and their interplay with regulatory T cells suggest further layers of complexity. This review summarizes state-of-the-art knowledge on T cell diversity and their induction, while revisiting the TH1/TH2 paradigm. With respect to these numerous contributors, it offers a new perspective on the pathogenesis of asthma, allergic rhinitis (AR) and atopic dermatitis (AD) incorporating recent discoveries in the field of T cell plasticity.