Natural killer T (NKT) cells are a heterogeneous group of T cells that recognise self and foreign lipids and glycolipids presented by CD1d, a non-polymorphic antigen-presenting molecule. They were originally described as expressing characteristics of both T and natural killer cells. Natural killer T cells are a distinct type of cells and should not be confused as natural killer cells or killer T cells. They constitute only approximately 1% of all peripheral blood T cells. Their function is to produce and release cytokines, kill other cells, and communicate with other cells in the immune system. They have been found to play a role in various autoimmune diseases.