[The Th2 theory in allergy: present and future directions].

Allergic diseases have been a model study for Th2 cells polarization and it is well known that the synthesis of the human IgE results from collaboration between Th2 and B cells through the cytokines such as IL-4 and IL-13 and surface molecules (CD40-CD40L). In the last decade, some surface molecules have been associated with human Th2 cells. Although recent studies suggest that the receptors of chemokines are the most related markers of Th2 cells, so far it has not found a specific marker to discriminate Th2 cells. The most recent studies suggest that Th1 and Th2 cells are not derived from different cellular lineages, but rather they can be derived from the same precursory Th cell and, under the influence of genetic environmental factors, they can be polarized. Also, some genes conferring susceptibility to production of Th2 cytokines have been located.