Jin, Zhongbo

Abstract Background/Purpose Interferon (IFN) gene expression signatures have been observed in whole blood and mixed immune cell populations in systemic lupus erythematosus (SLE), but the significance of this IFN signaling in immune cell subsets is not well understood. We examined gene expression in individual SLE patient monocytes to explore the impact of increased IFN-induced transcription in single cells. Methods CD14++CD16- classical monocytes and CD14dimCD16+ non classical monocytes from SLE patients were purified by magnetic separation. Single cells were isolated, and gene expression in each individual cell was examined by rtPCR. Results Monocytes from the same SLE patient blood sample demonstrated varying levels of IFN-induced gene expression. In classical monocytes, high IFN score correlated with CD32a, IL1B, and IL8 expression. In non-classical monocytes, high IFN score was correlated with a larger number of inflammatory mediators, including cytokines such as IL12, IL23, and IL15; the immune receptors CD36, CD32a, CD80, and TLR7; and inflammatory signaling genes such as RELA, STAT2, IRAK1, IRAK4, and MyD88. ConclusionWe observed striking diversity in the IFN responses of individual monocytes, demonstrating that IFN signaling has distinct effects upon classical and non-classical monocytes. Single cell studies can reveal effects of IFN on single immune cells and uncommon populations such as non-classical monocytes, which would be masked in whole blood or mixed cell populations.

Objectives Important findings can be masked in gene expression studies of mixed cell populations. We examined single-cell gene expression in SLE patient monocytes in the context of clinical and immunological features. Methods Monocytes were purified from patients with SLE and controls, and individually isolated for single-cell gene expression measurement. A panel of monocyte-related transcripts were measured in individual classical (CL) and non-classical (NCL) monocytes. Results Analyses of both CL and NCL monocytes demonstrated that many genes had a lower expression rate in SLE monocytes than in controls. Unsupervised hierarchical clustering of the CL and NCL data sets demonstrated independent clusters of cells from the patients with SLE that were related to disease activity, type I interferon (IFN) and medication use. Thus, each of these factors exerted a different impact on monocyte gene expression that could be identified separately, and a number of genes correlated uniquely with disease activity. We found within-cell correlations between genes directly induced by type I IFN-induced and other non–IFN-induced genes, suggesting the downstream biological effects of type I IFN in individual human SLE monocytes which differed between CLs and NCLs. Conclusions In summary, single-cell gene expression in monocytes was associated with a wide range of clinical and biological features in SLE, providing much greater detail and insight into the cellular biology underlying the disease than previous mixed-cell population studies.