CD16-positive circulating monocytes and fibrotic manifestations of systemic sclerosis

The objective of this study is to assess the association of clinical manifestations of systemic sclerosis (SSc) with the absolute count of circulating blood monocyte subpopulations according to their membrane expression of CD16. Forty-eight consecutive patients fulfilling the 2013 ACR/EULAR classification criteria for SSc were included in this cross-sectional study. CD16+ monocyte absolute count was defined by flow cytometry and confronted to the clinical characteristics of SSc patients. Twenty-three healthy donors (HD) were randomly selected for comparison. SSc patients had an increased number of total circulating blood monocytes compared to HD (p < 0.001). The CD16- subpopulation absolute count was increased in SSc patients compared to HD (p < 0.001) but was similar in limited SSc (lSSc) and diffuse SSc (dSSc). On the contrary, the CD16+ population absolute count was increased in dSSc compared to both HD and lSSc patients (dSSc 0.071 Giga/L (±0.034) vs HD 0.039 Giga/L (±0.030), p < 0.01, and dSSc 0.071 Giga/L (±0.034) vs lSSc 0.048 Giga/L (±0.024), p < 0.05). The CD16+ monocyte subpopulation absolute count was significantly correlated with the severity of skin fibrosis evaluated by the modified Rodnan skin score (p < 0.001). The CD16+ monocyte subpopulation was also associated with pulmonary fibrosis (p < 0.05), with the severity of the restrictive ventilatory defect evaluated by total lung capacity (p < 0.05) and with the pulmonary function impairment reflected by diffusing capacity of the lungs for carbon monoxyde measures (p < 0.01). These results suggest that CD16+ monocytes are associated with the main fibrotic manifestations of SSc and their role in the pathogenesis of fibrosis in this autoimmune disorder should therefore be further considered.