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 Th-2) cell-mediated immunity. Tim-4, which is preferentially expressed on macrophages and dendritic cells, is the natural ligand of Tim-1. 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 is connected to TIM-1-triggered Th2 responsiveness.