The role of helper T cell subsets in autoimmune diseases.

CD4 helper T cells can be divided into Th1 and Th2 subsets based upon the cytokines they produce. Th1 and Th2 cells have been found to be mutually antagonistic, leading to either Th1- or Th2-dominated responses upon immunization. In recent years, several authors have suggested that in chronic inflammatory autoimmune diseases such as diabetes, multiple sclerosis and rheumatoid arthritis, Th1 cells are pathogenic and Th2 cells are protective. Therefore, a successful deviation from a Th1-dominated to a Th2-dominated response could have clinical benefits for individuals suffering from these diseases. Unfortunately, data accumulated over recent years have not supported this approach, in particular regarding the protective role of Th2 cells. In this review we discuss these data and conclude that, at least using currently available tools, immune deviation from Th1 to Th2-dominated responses is ineffective unless started at very early (subclinical) stages of the disease. In addition, we examine some recent data suggesting that, under some circumstances, Th2 cells can be pathogenic.