PROJECT SUMMARY The overarching goal of this proposal is to systematically characterize an epigenetically distinct natural killer (NK) cell population with hypoacetylated histones. This NK cell subset is reduced in frequency in systemic lupus erythematosus (SLE) patients with increased disease activity. We will test the hypothesis that this NK cell subset, which we term “NKSLE cells”, has a distinct cell surface molecule profile, and is functionally different from other NK cells in cytolytic capacity and cytokine secretion upon activation. We will further examine if NK cell functions can be altered by experimental manipulation of histone acetylation. Our data will lay a strong foundation for future epigenomic studies on specific genes or genomic loci pivotal for lupus pathophysiology. The advent of single-cell technologies has greatly accelerated our understanding of immune system heterogeneity. Increasing evidence supports a compelling model in which pathologically important cells in SLE may represent only a small fraction of the highly complex immune system. This proposal builds upon this innovative concept, and will leverage cutting-edge technologies to interrogate the epigenetic and proteomic heterogeneity of NK cells, and their complex relationships. In Aim 1, we will employ highly multiplexed mass cytometry to monitor a broad array of functionally important NK cell markers, such as activating and inhibitory receptors, cell adhesion molecules, and those indicative of cytotoxicity activity, and histone acetylation abundance in individual NK cells. We will first benchmark NK cell heterogeneity in healthy blood donors, with a goal to identify cellular features associated with global histone acetylation level. Next, we will extend the analysis to SLE patients, whose NK cell compartments show reduced representation of cells with hypoacetylated histones. This study will reveal the phenotypic and functional characteristics of NKSLE cells. In Aim 2, we will investigate the functional differences between NK cells with differential histone acetylation content. Cytotoxicity and proinflammatory cytokine secretion are key immunological functions mediated by NK cells during a viral infection. Mass cytometry will be utilized to examine how differential histone acetylation abundance in individual NK cells is correlated with the degree of their immune response upon activation measured by degranulation markers, and cytokine production. Our analysis will first focus on NK cells isolated from healthy volunteers, and subsequently extend to those from lupus patients to better understand the clinical significance of NKSLE cell reduction in lupus. Lastly, as opposed to genetic mutations that are generally refractory to therapeutic interventions, epigenetic phenomena are largely reversible, making them attractive targets for developing new drugs. We will investigate the plasticity of NK cell functions by pharmacologically manipulating histone acetylation. Together,...