CD4 and asthma: Th2 cytokines, IL-4, IL-5 and IL-13 produced by activated CD4+ T cells, play a central role in the pathogenesis of asthma by controlling the key process of immunoglobulin E (IgE) production, growth of mast cells and the differentiation and activation of mast cells and eosinophils [32], [33], [34].