The role of Th2 type CD4+ T cells and Th2 type CD8+ T cells in asthma.

The cellular inflammatory responses which are seen in allergic and asthmatic diseases are viewed as being quite strongly dependent on the activities of T cells and their products. The major T cell subset involved appears to be the so-called CD4+ Th2 subset which produces interleukin-4 (IL-4) and interleukin-5 (IL-5). In vitro and in vivo experiments have indicated that IL-4 is a key regulator in these kinds of immune responses, not only switching B cells to IgE production, but acting on CD4+ T cells to drive their development towards a Th2 phenotype. Recent results have shown that the functional phenotype of CD8+ T cells can be switched from interferon gamma production to IL-4 and IL-5 production by the presence of IL-4. This could prove an especially important phenomenon since it is the production of interferon gamma by CD8 T cells which is seen as necessary for protection against virus infection. This short review updates our current knowledge of how IL-4 can act on CD4+ and CD8+ T cell subsets in in vivo models of asthma and allergic disease.