Characterization of monocyte/macrophage subsets in the skin and peripheral blood derived from patients with systemic sclerosis

Skin biopsy specimens from 6 healthy controls and 10 SSc patients (7 limited cutaneous SSc and 3 diffuse cutaneous SSc) were analyzed by immunohistochemistry using monoclonal antibody against CD68 (pan-macrophage marker), CD163 and CD204. Surface and/or intracellular protein expression of CD14 (marker for monocyte lineage), CD163 and CD204 was analysed by flow cytometry in PBMCs from 16 healthy controls and 41 SSc patients (26 limited cutaneous SSc and 15 diffuse cutaneous SSc). Statistical analysis was carried out using Mann-Whitney U test for comparison of means.In the skin from SSc patients, the number of CD163+ cells or CD204+ cells between the collagen fibers was significantly larger than that in healthy controls. Flow cytometry showed that the population of CD14+ cells was significantly greater in PBMCs from SSc patients than that in healthy controls. Further analysis of CD14+ cells in SSc patients revealed higher expression of CD163 and the presence of two unique peaks in the CD204 histogram. Additionally, we found that the CD163+ cells belong to CD14brightCD204+ population.This is the first report indicating CD163+ or CD204+ activated macrophages may be one of the potential fibrogenic regulators in the SSc skin. Furthermore, this study suggests a portion of PBMCs in SSc patients abnormally differentiates into CD14brightCD163+CD204+ subset. The subset specific to SSc may play an important role in the pathogenesis of this disease, as the source of CD163+ or CD204+ macrophages in the skin.Systemic sclerosis (SSc) is a multiorgan disease of unknown etiology that is characterized by activation of immune cells, production of autoantibodies and microvascular injury, leading to fibrosis [1-6]. Histopathological hallmarks of SSc are inflammatory infiltrates in early disease stages and accumulation of extracellular matrix proteins resulting in tissue fibrosis. Inflammatory infiltrates are dominated by macrophages and T cells [7,8].Monocytes, which leave from the bone