Butyrophilin-like 3 (BTNL3) is a member of the BTN/MOG Ig-superfamily which is coded by the BTNL3 gene, also known as COLF4100. BTNL3 is a 466 amino acid (aa) type I transmembrane protein that contains a 220 aa extracellular domain (ECD), a 21 aa helical transmembrane domain, and a 208 aa cytoplasmic domain. The ECD features both an IgV and IgC domain, which is commonplace in BTN/BTNL proteins, but the IgC domain is relatively weak. The ECD of human BTNL3 shares only 37% and 34% aa sequence identity with mouse (referred to as BTNL1) and rat, respectively. Human BTNL3 mRNA has been identified in many tissues including small intestine, colon, liver, lung, bone marrow and spleen tissue, and it is highly expressed in neutrophils. BTNL3 expression has also been found to be down-regulated in colon cancer tumors. The specific function of BTNL3, however, has yet to be fully elucidated. R&D in house data indicate that BTNL3 protein inhibits the secretion of IFN-gamma from anti-CD3 activated human T cells.