6-Sulfo LacNAc monocytes are quantitatively and functionally disturbed in systemic sclerosis patients.

Systemic sclerosis (SSc) is an autoimmune disease characterized by fibrosis, microangiopathy, and autoantibodies. We previously reported that circulating follicular helper T (cTfh) cells are increased in SSc and induce plasmablast differentiation. However, mechanisms leading to cTfh cell expansion and activation in SSc remain to be established. Tfh cells require IL-12 for their expansion and differentiation. 6-Sulfo LacNAc monocytes (slanMo), a subset of monocytes, have a higher capacity to produce IL-12 and to induce CD4+ T cell proliferation in comparison with dendritic cells (DC) or classical monocytes. The aim of this study was to perform a quantitative and functional analysis of monocytes and DC and to correlate them with cTfh cell expansion and clinical manifestations in SSc. Using flow cytometry, we analyzed different monocyte subsets including slanMo and DC from 36 SSc patients and 26 healthy controls (HC). In vitro culture experiments of sorted slanMo were performed for functional analysis and cytokine production. We observed that slanMo, intermediate and non-classical monocytes were increased in SSc in comparison with HC. Furthermore, the increase in slanMo cells was more potent in patients with diffuse SSc. We observed a significant positive correlation between slanMo and cTfh cell levels in SSc patients but not in HC. Other monocyte subsets did not correlate with cTfh cell expansion. In addition, we observed that in vitro, slanMo cells from SSc patients produced less IL-12 than slanMo from HC. SlanMo are increased in SSc and may participate in the activation of cTfh cells in SSc.