Objectives: To investigate serum levels, tissue/cellular expression of macrophage migration inhibitory factor (MIF) in patients with limited (lSSc) and diffuse (dSSc) systemic sclerosis.
Methods: 10 lSSc-patients, 10 dSSc-patients and 10 controls were enrolled. MIF serum levels were assayed by ELISA. MIF and its receptors CD74/CD44 were evaluated by immunohistochemistry on skin biopsies from patients with dSSc, lSSc (affected and not-affected skin) and controls. MIF levels were assessed (ELISA) in supernatants of healthy dermal microvascular endothelial cells (MVECs) and in control (CTR), non-affected SSc (NA) and affected (SSc) fibroblasts treated for 48 h with 10% control serum and 10% SSc-serum. MIF supernatant (ELISA) and mRNA (quantitative real-time PCR) levels were determined in SSc dermal fibroblasts and in control dermal fibroblasts untreated or stimulated at 6 h-24 h-48 h with bleomycin (50 mU/ml).
Results: Serum MIF was significantly higher in dSSc (18.7±4.1 ng/ml, p<0.001) and in lSSc (10.4±4.4 ng/ml, p<0.001) patients respect to controls (2.6±1.4 ng/ml). Enhanced MIF immunoreactivity was found in keratinocytes, fibroblasts, endothelium, sebaceous/sweat glands from lSSc/dSSc affected skin. Faint MIF immunoreactivity was found in control skin and not-affected skin of lSSc patients. No differences were found in CD74/CD44 receptors' analysis among control and dSSc/lSSc affected and non-affected skin. MVECs and fibroblasts (CTR, NA and SSc) produced significantly more MIF, when stimulated with SSc serum respect to control-serum (p<0.001). Finally, MIF mRNA levels significantly increased at 6h (p<0.001) and decreased at 48 h (p<0.001) in control fibroblasts treated with bleomycin compared to control untreated. Simultaneously, MIF supernatant protein levels increased after 48 h (p<0.01) in bleomycin-treated fibroblasts respect to untreated ones.
Conclusions: These results suggest that MIF could be implicated in the pathogenesis of SSc, probably acting as protective factor against the SSc stressful conditions.