Abbreviations used: LAK, lymphokine-activated killer; m157-Tg, m157 transgenic; MCMV, murine cytomegalovirus; poly I: C, polyinosinic:polycytidylic acid.The online version of this article contains supplemental material. Natural killer (NK) cell tolerance mechanisms are incompletely understood. One possibility is that they possess self-specifi c activation receptors that result in hyporesponsiveness unless modulated by self -major histocompatability complex (MHC) -specifi c inhibitory receptors. As putative self-specifi c activation receptors have not been well characterized, we studied a transgenic C57BL/6 mouse that ubiquitously expresses m157 (m157-Tg), which is the murine cytomegalovirus (MCMV) -encoded ligand for the Ly49H NK cell activation receptor. The transgenic mice were more susceptible to MCMV infection and were unable to reject m157-Tg bone marrow, suggesting defects in Ly49H + NK cells. There was a reversible hyporesponsiveness of Ly49H + NK cells that extended to Ly49H-independent stimuli. Continuous Ly49H -m157 interaction was necessary for the functional defects. Interestingly, functional defects occurred when mature wild-type NK cells were adoptively transferred to m157-Tg mice, suggesting that mature NK cells may acquire hyporesponsiveness. Importantly, NK cell tolerance caused by Ly49H -m157 interaction was similar in NK cells regardless of expression of Ly49C, an inhibitory receptor specifi c for a self-MHC allele in C57BL/6 mice. Thus, engagement of self-specifi c activation receptors in vivo induces an NK cell tolerance effect that is not affected by self-MHC -specifi c inhibitory receptors.

Cytokines regulate lymphocyte development and differentiation, but precisely how they control these processes is still poorly understood. By using microarray technology to detect cytokineinduced genes, we identified a cDNA encoding Cybr, which was

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