Regulation of Immunity by Butyrophilins

Butyrophilin molecules (commonly contracted to BTN), collectively take their name from the eponymous protein in cow's milk. They are considered to be members of the B7 family of costimulatory receptors, which includes B7.1 (CD80), B7.2 (CD86), and related molecules, such as PD-L1 (B7-H1, CD274), ICOS-L (CD275), and B7-H3 (CD276). These coreceptors modulate T cell responses upon antigen presentation by major histocompatibility complex and cognate αβ T cell receptor engagement. Molecules such as BTN3A1 (CD277), myelin oligodendrocyte glycoprotein, and mouse Skint1 and Btnl2, all members of the butyrophilin family, show greater structural and functional diversity than the canonical B7 receptors. Some butyrophilins mediate complex interactions between antigen-presenting cells and conventional αβ T cells, and others regulate the immune responses of specific γδ T cell subsets by mechanisms that have characteristics of both innate and adaptive immunity.