Expression and function of surface molecules on Th1 and Th2 lymphocytes.

Since 1986, when the existence of two distinct T helper (Th) cell subsets was first theorized, a large body of evidence has been produced to support and confirm such hypothesis. It is now accepted, therefore, that Th1 and Th2 cells, which are categorized based on cytokine production, develop different immune responses and are involved in the pathogenesis of autoimmune and allergic diseases. Recently, Th1 and Th2 cells have been shown to differ not only based on type of cytokines produced upon activation, but also on expression of several membrane molecules. These membrane molecules participate in the formation of a complex phenotype during T cell differentiation and effector functions depending on their specific role in distinct functional states. Here, we review a number of Th1- or Th2-associated molecules involved in different cell processes, such as cell adhesion and migration, apoptosis, response to cytokines or chemokines. For some of these molecules evidence exists to support selective expression by either Th cell subset, whereas other molecules have not been conclusively shown to be restricted to a specific Th cell subset. Knowledge of these specific membrane markers, which might allow identification of Th1 or Th2 cells in different functional states, is crucial to a deeper understanding of the role played by these cells in the pathogenesis of autoimmune and allergic diseases as well as to follow up the response to specific therapies.