The T cell immunoglobulin and mucin domain containing protein (TIM) family encodes cell surface receptors that are involved in the regulation of T helper (Th) -1 and -2 cell-mediated immunity. Studies have shown that TIM 4, which is preferentially expressed on macrophages and dendritic cells, is the natural ligand of TIM 1, and that this binding leads to T-cell expansion and cytokine production. Unlike other members of the TIM family, TIM 4 lacks a putative tyrosine phosphorylation signal sequence in its intracellular domain. The TIM 4 gene maps to a locus associated with predisposition to asthma in both mice and humans and with its connection to TIM 1-triggered Th2 responsiveness, may be considered as a candidate disease/predisposition gene for asthma.