CD4þ T cells can develop into T helper cells (Th1 and Th2 cells) characterized by the production of different cytokines, such as interleukin-2 (IL-2) and interferon-g from Th1 cells, and IL-4 and IL-13 from Th2 cells. Th2 cytokines are associated with allergic reactions and maturation of mast cells, but have recently also been implicated in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) (Pedotti et al., 2003). Mast cells are involved in allergy as well as in innate and acquired immunity (Galli et al., 2005), including T-cell-mediated disorders (Gregory et al., 2006) and autoimmune disorders (Benoist and Mathis, 2002). Mast cells and T cells could interact in a variety of immune responses (Pedotti et al., 2003; Nakae et al., 2005),including many inflammatory diseases (Theoharides and Kalogeromitros, 2006). Mast cells are also located at the blood–brain barrier (BBB), especially in the choroid plexus, diencephalon and the third ventricle (Silver et al., 1996), as well as at MS plaques (Ibrahim et al., 1996). There, mast cells could regulate BBB permeability (Esposito et al., 2001), disruption of which precedes clinical or pathological signs of MS (Stone et al., 1995); this could attract T cells and superactivate them.
