Helper T cell subsets: Development, function and clinical role in hypersensitivity reactions in the modern perspective.

Helper T cells are traditionally classified into T helper 1 (T1) and T helper 2 (T2). The more recent discoveries of T helper 17 (T17), follicular helper T cells (T) and regulatory T cells (T) enhanced our understanding on the mechanisms of immune function and hypersensitivity reactions, which shaped the modern perspective on the function and role of these different subsets of helper T cells in hypersensitivity reactions. Each subset of helper T cells has characteristic roles in different types of hypersensitivity reactions, hence giving rise to the respective characteristic clinical manifestations. The roles of helper T cells in allergic contact dermatitis (T1-mediated), drug rash with eosinophilia and systemic symptoms (DRESS) syndrome (T2-mediated), and acute generalised exanthematous pustulosis (AGEP) (T17-mediated) are summarised in this article, demonstrating the correlation between the type of helper T cell involved and the clinical features. T plays crucial roles in antibody class-switch recombination; they may be implicated in antibody-mediated hypersensitivity reactions, but further research is warranted to delineate their exact pathogenic roles. The helper T cell subsets and their specific cytokine profiles implicated in different hypersensitivity reactions could be potential treatment targets by biologics, but more clinical trials are warranted to establish their clinical effectiveness.