Antigen stimulation of immune cells triggers Ca++ entry through Ca++ release-activated Ca++ (CRAC) channels (1 for review). ORAI2 is one of two mammalian homologs to ORAI1, a recently identified four-transmembrane spanning protein that is an essential component of CRAC (2). Like ORAI1, ORAI2 has been shown to function as a highly selective Ca++ plasma membrane channel that is gated through interactions with STIM1, the store-activated endoplasmic reticulum Ca++ sensor (3,4), although at a lesser efficacy than ORAI1 (4,5). This antibody is predicted to have no cross-reactivity to ORAI1 or ORAI3.