Transcriptional profiling reveals functional dichotomy between human slan+ non-classical monocytes and myeloid dendritic cells

Abstract: Human 6-sulfo LacNac (slan)+ cells have been subject to a paradigm debate. They have previously been classified as a distinct dendritic cell (DC) subset. However, evidence has emerged that they may be more related to monocytes than to DC. To gain deeper insight into the functional specialization of slan+ cells, we have compared them with both conventional myeloid DC subsets (CD1c+ and CD141+) in human peripheral blood. Using genome-wide transcriptional profiling as well as extensive functional tests, we clearly show that slan+ cells form a distinct, non-DC-like, population. They cluster away from both DC subsets and their gene expression profile evidently suggests involvement in distinct inflammatory processes. An extensive comparison with existing genomic data sets also strongly confirmed the relationship of slan+ with the monocytic compartment rather than with DC. From a functional perspective, their ability to induce CD4+ and CD8+ T cell proliferation is relatively low. Combined with the finding that antigen presentation by MHC class II is at the top of under-represented pathways in slan+ cells, this points to a minimal role in directing adaptive T cell immunity. Rather, the higher expression of complement receptors on their cell surface, together with their high secretion of IL-1 and IL-6, imply a specific role in innate inflammatory processes, which is consistent with their recent identification as non-classical monocytes. This study extends our knowledge on DC/monocyte subset biology under steady state conditions and contributes to our understanding of their role in immune-mediated diseases and their potential use in immunotherapeutic strategies.

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van Leeuwen-Kerkhoff N, Lundberg K, Westers TM, Kordasti S, Bontkes HJ, de Gruijl TD, Lindstedt M, van de Loosdrecht AA