Abstract
It has recently been appreciated that NK cells exhibit many features reminiscent of adaptive immune cells. Considerable heterogeneity exists with respect to the ligand specificity of individual NK cells and as such, a subset of NK cells can respond, expand, and differentiate into memory-like cells in a ligand-specific manner. MHC I-binding inhibitory receptors, including those belonging to the Ly49 and KIR families, are expressed in a variegated manner, which creates ligand-specific diversity within the NK cell pool. However, how NK cells determine which inhibitory receptors to express on their cell surface during a narrow window of development is largely unknown. In this manuscript, we demonstrate that signals from activating receptors are critical for induction of Ly49 and KIR receptors during NK cell development; activating receptor-derived signals increased the probability of the Ly49 bidirectional Pro1 promoter to transcribe in the forward versus the reverse direction, leading to stable expression of Ly49 receptors in mature NK cells. Our data support a model where the balance of activating and inhibitory receptor signaling in NK cells selects for the induction of appropriate inhibitory receptors during development, which NK cells use to create a diverse pool of ligand-specific NK cells.
Natural killer (NK) cells are important cells of the immune system, because they kill abnormal cells such as those infected with viruses or have become cancerous. These abnormal cells can lose proteins known as MHC molecules, which are recognized by inhibitory receptors on NK cells. Thus, when an NK cell interacts with a cell with decreased MHC, the NK cell is disinhibited and can kill the target cell. Each NK cell carries a unique assortment of these inhibitory receptors. However, how developing NK cells determine which inhibitory receptors to put on the NK cell’s surface during development is unknown. In this study, we show that signals generated through NK cell activating receptors are important for inducing a subset of inhibitory receptors on NK cells during development. We propose that the NK cell has an increased chance of acquiring an inhibitory receptor until a balance between activating and inhibitory receptor signals is achieved. This process ensures that NK cells can properly detect abnormal cells that have lost MHC.
During the development of natural killer (NK) cells, activating receptor signaling drives the acquisition of inhibitory receptors during development, leading to the creation of a diverse pool of ligand-specific NK cells.
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