Th1-specific cell surface protein Tim-3 regulates macrophage activation and severity of an autoimmune disease

Activation of naive CD4+ T-helper cells results in the development of at least two distinct effector populations, Th1 and Th2 cells1,2,3. Th1 cells produce cytokines (interferon (IFN)-γ, interleukin (IL)-2, tumour-necrosis factor (TNF)-α and lymphotoxin) that are commonly associated with cell-mediated immune responses against intracellular pathogens, delayed-type hypersensitivity reactions4, and induction of organ-specific autoimmune diseases5. Th2 cells produce cytokines (IL-4, IL-10 and IL-13) that are crucial for control of extracellular helminthic infections and promote atopic and allergic diseases4. Although much is known about the functions of these two subsets of T-helper cells, there are few known surface molecules that distinguish between them6. We report here the identification and characterization of a transmembrane protein, Tim-3, which contains an immunoglobulin and a mucin-like domain and is expressed on differentiated Th1 cells. In vivo administration of antibody to Tim-3 enhances the clinical and pathological severity of experimental autoimmune encephalomyelitis (EAE), a Th1-dependent autoimmune disease, and increases the number and activation level of macrophages. Tim-3 may have an important role in the induction of autoimmune diseases by regulating macrophage activation and/or function.