Capacity of myeloid and plasmacytoid dendritic cells especially at mature stage to express and secrete HLA-G molecules.

Human leukocyte antigen (HLA-G), a class Ib major histocompatibility complex molecule, is potentially relevant in the immune response through its various immune cell functions. Its expression noticed in some malignancies has also been shown on macrophages and dendritic cells (DC) in tumoral and inflammatory diseases. As DC constitute a key component in the immune response, this work aimed at assessing the expression of HLA-G at transcriptional and proteic levels during differentiation and maturation of the different DC subsets. We show that HLA-G transcription was induced during CD34+-derived DC differentiation and is associated with a cell-surface expression in half of cases and with a substantial secretion of soluble HLA-G in all cases. Results were very similar for monocyte-derived DC, but there was still a weak HLA-G cell-surface expression and a lower level of secretion. On the contrary, HLA-G transcription was weak in plasmacytoid DC without any HLA-G cell-surface expression and with a basal level of secretion. The mechanisms involved in HLA-G expression appear transcriptional and post-transcriptional. However, the amount of HLA-G transcripts and the expression of the protein are not related. HLA-G expression or secretion by DC may have negative consequences on the function of effective immune cells and also on DC themselves via the interaction with inhibitory receptors expressed by these cells. The capacity of DC to express or secrete HLA-G should be studied in the context of cellular therapy using DC in addition to its suppressive action in immune response.