Synovial CD4+ T-cell-derived GM-CSF supports the differentiation of an inflammatory dendritic cell population in rheumatoid arthritis

Abstract

ObjectiveA population of synovial inflammatory dendritic cells (infDCs) has recently been identified in rheumatoid arthritis (RA) and is thought to be monocyte-derived. Here, we investigated the role and source of granulocyte macrophage-colony-stimulating factor (GM-CSF) in the differentiation of synovial infDC in RA.MethodsProduction of GM-CSF by peripheral blood (PB) and synovial fluid (SF) CD4+ T cells was assessed by ELISA and flow cytometry. In vitro CD4+ T-cell polarisation experiments were performed with T-cell activating CD2/CD3/CD28-coated beads in the absence or presence of pro-Th1 or pro-Th17 cytokines. CD1c+ DC and CD16+ macrophage subsets were flow-sorted and analysed morphologically and functionally (T-cell stimulatory/polarising capacity).ResultsRA-SF CD4+ T cells produced abundant GM-CSF upon stimulation and significantly more than RA-SF mononuclear cells depleted of CD4+ T cells. GM-CSF-producing T cells were significantly increased in RA-SF compared with non-RA inflammatory arthritis SF, active RA PB and healthy donor PB. GM-CSF-producing CD4+ T cells were expanded by Th1-promoting but not Th17-promoting conditions. Following coculture with RA-SF CD4+ T cells, but not healthy donor PB CD4+ T cells, a subpopulation of monocytes differentiated into CD1c+ infDC; a process dependent on GM-CSF. These infDC displayed potent alloproliferative capacity and enhanced GM-CSF, interleukin-17 and interferon-γ production by CD4+ T cells. InfDC with an identical phenotype to in vitro generated cells were significantly enriched in RA-SF compared with non-RA-SF/tissue/PB.ConclusionsWe demonstrate a therapeutically tractable feedback loop of GM-CSF secreted by RA synovial CD4+ T cells promoting the differentiation of infDC with potent capacity to induce GM-CSF-producing CD4+ T cells.

Dendritic cell recruitment and activation in autoimmunity

“…However, it was shown that the abundance of IL-7 in RA joints plays a critical role in overcoming PD-1-mediated inhibition of T cells, leading to the prevalence of T-activating effects [164,165]. Furthermore, GM-CSF produced by synovial CD4 þ T cells supported the differentiation and activation of infDC, thus promoting a local inflammatory amplification loop [166]. In T1D, a protective role of TLR2 deficiency was described in NOD mice [167].…”

T Cell-Derived GM-CSF, Regulation of Expression and Function

“…CD4 + T cell-secreted GM-CSF was required for the generation of monocyte-derived inflammatory dendritic cells (infDCs) and disease progression for acute inflammatory arthritis and peritonitis in mice [30]. In human rheumatoid arthritis (RA), synovial CD4 + T cells were found to be a major source of GM-CSF that strongly promoted infDC differentiation [31]. In juvenile idiopathic arthritis, the frequency of GM-CSF-producing CD4 + T cells in synovial fluid was significantly correlated with GM-CSF protein level as well as serum erythrocyte sedimentation rate, an indicator of inflammation [32].…”

The role of human CD1c+ DCs at activating innate and adaptive immune responses

“…Noster et al further demonstrated that human memory CD4 + T cells cultured in the presence of IL-1β and IL-23 do not induce GM-CSF compared to IL-12p70 alone (Noster et al, 2014). In humans, high levels of GM-CSF have been documented in RA and multiple sclerosis (Noster et al, 2014, Reynolds et al, 2015. Duhen et al reported the synergy between IL-1β and IL-12p70 induced high levels GM-CSF from human Th17 cells (Duhen and Campbell, 2014).…”

“…Indeed, Noster et al and Reynolds et al demonstrated that GM-CSF production by reactivated memory CD4 + T cells was suppressed by IL-1β, IL-6 or IL-23; while IL12p70 significantly enhanced GM-CSF production (Noster et al, 2014, Reynolds et al, 2015.…”

“…However, GM-CSF production by human memory CD4 + T cells could also be induced by IL-15 and IL-2 in a STAT5-dependent manner (Noster et al, 2014, Reynolds et al, 2015 PBMCs from healthy controls (Ramesh et al, 2014). Importantly, MDR1 activity was restricted to a subset of CD161 + memory CD4 + T cells.…”