LAUSR

Natural killer (NK) cells recognize virally infected cells and tumors. NK cell function depends on balanced signaling from activating receptors, recognizing products from tumors or viruses, and inhibitory receptors (such as KIR/Ly49), which recognize major histocompatibility complex class I (MHC-I) molecules. KIR/Ly49 signaling preserves tolerance to self but also conveys reactivity toward MHC-I–low target cells in a process known as NK cell education. Here, we found that NK cell tolerance and education were determined by the subcellular localization of the tyrosine phosphatase SHP-1. In mice lacking MHC-I molecules, uneducated, self-tolerant Ly49A+ NK cells showed accumulation of SHP-1 in the activating immune synapse, where it colocalized with F-actin and the signaling adaptor protein SLP-76. Education of Ly49A+ NK cells by the MHC-I molecule H2Dd led to reduced synaptic accumulation of SHP-1, accompanied by augmented signaling from activating receptors. Education was also linked to reduced transcription of Ptpn6, which encodes SHP-1. Moreover, synaptic SHP-1 accumulation was reduced in NK cells carrying the H2Dd-educated receptor Ly49G2 but not in those carrying the noneducating receptor Ly49I. Colocalization of Ly49A and SHP-1 outside of the synapse was more frequent in educated compared with uneducated NK cells, suggesting a role for Ly49A in preventing synaptic SHP-1 accumulation in NK cell education. Thus, distinct patterning of SHP-1 in the activating NK cell synapse may determine NK cell tolerance. Description The spatial patterning of the tyrosine phosphatase SHP-1 in mouse NK cells may determine self-tolerance. Location matters for NK cell education Natural killer (NK) cells recognize and kill virally infected cells and tumor cells. NK cell activation depends on the balance in signaling between activating receptors, which recognize stress-induced cellular ligands, and inhibitory receptors, recognizing MHC class I (MHC-I) molecules, markers of self and determinants of tolerance. During NK cell development, inhibitory receptor signaling ensures that NK cells tolerate self and can respond to activating ligands, a process known as education. Schmied et al. compared uneducated and educated mouse NK cells and found that education altered the subcellular localization of the tyrosine phosphatase SHP-1, which normally inhibits NK cell activation. During education, inhibitory receptors sequestered SHP-1, suggesting a model in which SHP-1 is prevented from accumulating at activating immune synapses between NK cells and their targets, thus facilitating target cell killing. These findings suggest that the spatial patterning of SHP-1 in NK cell synapses through education may facilitate self-tolerance. —JFF