Butyrophilin-Like Protein 9 (BTNL9) is single-pass type I membrane protein member of the BTN/MOG family that belongs to the immunoglobulin superfamily. BTNL9 consists of two domains: one B30.2/SPRY domain and one Ig-like V-type (immunoglobulin-like) domain. Human BTNL9 mRNA has been identified in adipose, lung, thymus, spleen, colon, and cardiac tissues, but its highest levels of expression were found in B cells. BTNL9 expression has also been found to be down-regulated in colon cancer tumors.