CD4 + T cells and IL-4-mediated support of Th1 immune responses

Abstract

Sustained CD8+ T-cell responses are often dependent on help from CD4+ T cells to mediate an effective outcome against disease. The help provided by CD4+ T cells is not well characterized, but might be mediated by the production of cytokines, such as interleukin-2 (IL-2), or by the activation of professional antigen-presenting cells. Moreover, different subsets of CD4+ T cells have been characterized based on their pattern of cytokine secretion. Classically, these have included two groups of CD4+ T cells: (1) T helper 1 (Th1) cells associated with the production of IL-2 and interferon-γ (IFN-γ); and (2) Th2 cells associated with the production of IL-4 and IL-10. Whereas Th1 cells can bias immune activity toward a more cellular-based response, Th2 cells can bias toward a humoral-based response. Although these simple distinctions have proved useful, recent reports suggest a more complex reality. For example, although IL-4 has been shown as crucial in the induction of a Th2-biased immune response, it might also be crucial in the development of some Th1-biased immune responses.