The role of T helper subsets in autoimmunity and allergy.

The classification of T helper (T(H)) cells in subsets has progressively expanded and more effector subsets, besides T(H)1 and T(H)2, have been documented. These include follicular helper T cells (T(FH)), and the more recent T(H)17, 'T(H)9', and 'T(H)22'. In addition, T(H) are no longer thought of as terminally committed effector cells, with plasticity now recognized. Identification of the molecular mechanisms that drive differentiation of T(H) cells has established a link between environmental factors and T(H) subsets, with regard to both the initiation and severity of immune disorders. The role of T(H) in autoimmune-disorders and allergic-disorders is now re-evaluated, with current data suggesting a central role for T(H)17 in orchestrating adaptive-immune responses, while T(FH) are instrumental in coordinating B cell immunity.