Mouse Tim-3 (T-cell Immunoglobulin- and Mucin -domain- containing molecule -3) is a type I transmembrane protein that contains an immunoglobulin V-type domain followed by a mucin-like domain in its extracellular region.1 Tim-3 is expressed on Th1 and Tc1 cells and is hypothesized to regulate macrophage activation.1 Binding of Tim-3 to Tim-3 Ligand on CD4+ T cells suggests that these proteins function in regulating Th1 cell expansion and/or activation,2 and suggests a role for Tim-3 in inducing tolerance.3 Mouse models utilizing antibodies to Tim-3 reveal a role for Tim-3 in immune-mediated diseases such as asthma and multiple sclerosis.2, 4