Types of T helper cells 

T helper cells (CD4+ T  helper cells) can be divided into two major subsets termed , based on their pattern of secreted cytokines. T cells expressing cytokine patters of both patterns have been called Th0 cells. Naive CD4+ Th- serve as precursors of Th1 and Th2 cells. IFN? producing  T helper subset 1 (Th1) cells are imiportant in cell mediated and humoral immuntiy against intracellular pathogens, whereas TH2 cells, which secrete IL-4, IL-5, IL-10 and IL-13 direct cellular and humoral immunity against extracellular pathogens. 

The tendency of a response to become polarized toward aTH1 or TH2 effectors is influenced by a combination of host genetic factors and the type and amount of antigen that is encountered. In addition, cytokines produced by cells of the innate immune system are the most important. 

T helper 17 cells (Th17): are a more recent discovered subset of T hper cells which produce IL-17. Excessive amounts of these cells are thought to be significant in autoimmune disease like Multiple Sclerosis. Th17 cells have been shown to be important in cases of infection with various bacterial and fungi infections.

Within the CD4+ T cell subset, at least three different types of cells with suppressive function may exist; CD25+CD4+T cells, type 1 T regulatory (Tr1) cells, and Th3 cells. These cells appear to be distinguishable based on their cytokine production profile, and their ability to suppress immune responses via direct cell-to-cell interactions or secretion of immunosuppressive cytokines. Cells producing high amounts of TGF-B have been termed Th3.

Despite the important functional division between Th1-th2 cells, it is important to understand that the variation in the cytokines secreted by these 2 subsets is not always absolute.