Th1/Th2 Immune Balance and Other T Helper Subsets in IgG4-Related Disease.

IgG4-related disease (IgG4-RD) is a systemic disease characterized by elevated serum IgG4 levels and a strong infiltration of IgG4-positive plasma cells in various organs. IgG4-RD patients also frequently suffer from allergic diseases, including asthma and atopic dermatitis. It is well known that T helper type 2 (Th2) cells have an important role in the initiation of allergic diseases, and Th2 cytokines such as interleukin (IL)-4 and IL-13 promote class switching to IgG4. Therefore, IgG4-RD is considered to be a Th2-predominant disease. However, other Th subsets, including regulatory T cells and T follicular helper cells, have recently received increasing attention with regard to the pathogenesis of IgG4-RD. Exploring the interconnected network of Th subsets in IgG4-RD is a highly promising field of investigation. In this review, we focus on the localization and functions of individual Th subsets to clarify the involvement of these cells in the pathogenesis of IgG4-RD.