Recombinant Mouse TIM-1/KIM-1/HAVCR Protein

TIM‑1 (T cell‑immunoglobulin‑mucin; also KIM‑1 and Tapr) is a 70 ‑ 80 kDa, type I transmembrane glycoprotein member of the TIM family of immunoglobulin superfamily molecules (1, 2, 3, 4). This gene family is involved in the regulation of Th1 and Th2‑cell‑mediated immunity. In mouse, there are eight known TIM genes (# 1 ‑ 8) vs. only three genes in human (# 1, 3 & 4) (1, 2). Mouse TIM‑1 and ‑2 are counterparts of human TIM‑1, while mouse TIM‑5 through TIM‑8 have no human counterparts (2). Mouse TIM‑1 (isoform 2) is synthesized as a 282 amino acid (aa) precursor that contains a 21 aa signal sequence, a 193 aa extracellular domain (ECD), a 21 aa transmembrane segment and a 47 aa cytoplasmic domain (5, 6). The ECD contains one V‑type Ig‑like domain and a mucin region characterized by multiple T‑S‑P motifs. The mucin region undergoes extensive O‑linked glycosylation. The mouse TIM‑1 gene is highly polymorphic and, based on rat, may undergo alternate splicing (4, 6). One isoform (termed isoform 1) possesses a 23 aa insertion after Pro182 (GenBank # NP_599099). Another splice variant (of isoform 1) shows a 15 aa deletion in the mucin region of the ECD (6). This difference is associated with a decreased susceptibility to asthma. In human, TIM‑1 is known to circulate as a soluble form that arises from cleavage by an undefined MMP, releasing an 85 ‑ 90 kDa soluble molecule (7). In mouse, a 60 ‑ 65 kDa soluble form has also been detected (in urine) that presumably arises from proteolytic processing (8). In‑house data from R&D Systems Inc. has demonstrated the presence of soluble TIM‑1 in mouse circulation. The ECD of mouse TIM‑1 shares 37% and 81% aa sequence identity with human and rat TIM‑1 ECD, respectively. There are at least three reported ligands for TIM‑1, and include TIM‑4, phosphatidlyserine and the hepatitis A virus (3, 9, 10). However, still others are believed to exist, and based on the ligand for TIM‑3, one might be an S‑type lectin (11). TIM‑1 ligation induces T cell proliferation and promotes cytokine production (1, 11). In particular, it induces IL‑4 production, and requires the TIM‑1 cytoplasmic tyrosine phosphorylation motif (5).