Allergies - A T cells perspective in the era beyond the T H 1/T H 2 paradigm

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