ABCB (TAP) The half transporters in this subfamily include ABCB2 (TAP1) and ABCB3 (TAP2) that need to form a functional heterodimer to transport peptides into the ER providing the antigens presented by class I HLA molecules. Specific Tap1/Tap2 polymorphisms are associated with ankylosing spondylitis (Qian et al., 2017), celiac disease (Powis et al., 1993), Graves’ disease (Rau et al., 1997), and other autoimmune diseases (de la Salle et al., 1994). ABCB9, a half transporter and the closest homolog of the TAPs, has been localized to lysosomes. The other four half transporters, ABCB6, ABCB7, ABCB8, and ABCB10, localize to the mitochondria, where they function in iron metabolism and the transport of Fe/S protein precursors (Dean, 2002). ABCB10 is also associated with protection from oxidative stress, and it is essential for erythropoiesis and recovery from cardiac ischemia-reperfusion (Liesa, Qiu, & Shirihai, 2012).