Activation-induced colocalisation of SCAMP5 with IFN in human plasmacytoid dendritic cells

Introduction Plasmacytoid dendritic cells (pDCs) are the main producers of type I interferon (IFN) in SLE. pDCs express high secretory carrier membrane protein 5 (SCAMP5). Recent work in transfected HEK cells connects SCAMP5 to the type I IFN secretory pathway. To further study the role of SCAMP5 in IFN alpha secretion by pDCs, we focused on the subcellular distribution of SCAMP5 in human pDCs freshly isolated from peripheral blood. Methods We measured SCAMP5 expression by flow cytometry in peripheral blood mononuclear cells of healthy subjects (n=8). Next, we assessed the colocalisation of SCAMP5 with IFN alpha in pDCs of healthy subjects (n=4) by evaluating bright detail similarity (BDS) scores using ImageStream technology. Results We confirm that SCAMP5 is highly expressed by pDCs derived from peripheral blood. In activated pDCs, we show that SCAMP5 colocalises with IFN alpha (mean BDS 2.0 +/- 0.1; BDS >2.0 in 44% of pDCs). Conclusion SCAMP5 colocalises with IFN alpha in activated human pDCs, in support of a role of this trafficking protein in the secretion of type I IFN by pDCs.