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

Abstract 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 T H 1/T H 2 paradigm assumes that a dominance of T H 2 cell activation and an inadequate T H 1 cell response are responsible for the development of allergies. However, the characterization of additional T helper cell subpopulations such as T H 9, T H 17, T H 22, T H GM-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 T H 1/T H 2 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.