After activation, T cells differentiate into distinct effector populations according to the particular cytokine environment that surrounds them. High levels of IFN-γ generate a Th1 population that contributes to protection against bacteria and viruses, whereas an environment of IL-4 leads to development of Th2 cells that are protective against helminths (
1). Allergic asthma is generally held to occur as a consequence of a dysregulated Th2 response to environmental allergens, as it is characterized by increased levels of the Th2 cytokines IL-4, -5, -9, and -13 (
2–
4). Manipulation of Th2 function has been proposed as a novel strategy for treatment of asthma, and enhancing Th1 responses in allergic individuals has been proposed as one method of such a strategy. In mice, transfer of Th1 cells has been shown to down-regulate pathology induced by transfer of Th2 cells alone, and this inhibition has been shown to be IFN-γ dependent (
5).
T cell Ig and mucin domain–containing molecule-3 (Tim-3) was described as a transmembrane protein preferentially expressed on Th1 cells (
6). In a Th1-mediated model of experimental allergic encephalomyelitis (EAE), in vivo neutralization of Tim-3 resulted in increased disease severity. Two further studies suggested that Tim-3 function was required for peripheral tolerance and acquisition of transplantation tolerance, respectively (
7,
8). In addition, galectin-9 has recently been identified as the ligand for Tim-3, and it has been demonstrated that administration of galectin-9 induced selective death of Th1 cells and inhibited the development of EAE (
9). Collectively, these studies implied that signaling through Tim-3 may negatively regulate Th1 responses, and thus suppression of Tim-3 may inhibit Th2 responses such as allergic disease through enhancement of a Th1 response.
Tim-3 belongs to a novel family of genes that map to a region of chromosome 11 termed
T cell and airway phenotype regulator (
Tapr), which confers reduced Th2 responsiveness and protects against airway hyperreactivity (AHR) (
10). Experiments with mice have shown that the
Tapr locus might regulate Th cell differentiation during primary antigen-specific responses (
10). Currently, the Tim gene family has eight members, Tim-1–8, and genomic analysis has revealed that an equivalent Tim family of genes exists in humans (
11). Polymorphisms in human Tim-1 and -3 have been associated with atopy, suggesting that the Tim family may have functional roles in human allergic diseases (
12). In mouse, Tim-1–3 are reciprocally expressed by Th2 and Th1 cells during T cell differentiation, but their roles in the development of allergy and atopy have not yet been investigated. Therefore, we have used a monoclonal antibody to Tim-3 to determine the effect of Tim-3 blockade on development of allergen-induced airway pathology and AHR in mice.