GM-CSF strongly enhances TLR9-induced phagocytic capacity and activation of human plasmacytoid dendritic cells

J.M. Ruben, G. Garcia-Romo, E. Breman, S. van der Kooij, A. Redeker, R. Arens, C. van Kooten

Friday 16 march 2018

10:05 - 10:10h at Willem Burger Foyer

Categories: Basic, Session (poster)

Parallel session: Poster session 8: Basic translational research

We have previously demonstrated that plasmacytoid dendritic cells (pDC) infiltrate the kidney in close proximity of tubular epithelial cells during rejection, and that conditioned medium (CM) of renal epithelial cells strongly enhanced TLR9-induced pDC activation. Here, we further evaluated the functional consequences of CM on pDC activation and set out to identify the responsible factor(s).

Activation of negatively selected human pDC by CMV or low dose CpG (0.5 µg/mL) in the presence of CM resulted in a strong increased capacity to ingest apoptotic cells, compared to non-primed pDC (59% vs 11%). Moreover, primed pDC produced 10-fold higher amounts of IFNα, showed a superior phenotypic maturation (CD40/80/83/86/CCR7), and induced vigorous allogeneic T cell proliferation, as compared to their non-primed counterparts (60% vs 4%). Following Luminex analysis, we identified GM-CSF as one of the candidate factors present in CM. Supplementation of pDC cultures with GM-CSF mimicked this functional activity. Neutralizing anti-GM-CSF antibodies showed full inhibition of recombinant GM-CSF, whereas they showed a significant, but partial inhibition of CM, suggesting the presence of additional factors in CM.

In conclusion, we show that GM-CSF is one of the factors important for priming of pDC, lowering their TLR9 activation-threshold and enhancing their function as APC.