Background Anti Neutrophil Cytoplasmic Antibodies (ANCA) – associated vasculitides (AAV) are characterized by small vessel injury and in some cases granulomatous lesions and glomerular inflammation. The pathogenic bases of clinical phenotypes are incompletely understood, but monocyte/macrophages are possibly involved in the perpetuation of tissue injury. Macrophage colony stimulating factor (M-CSF) is a promoter of monocyte recruitment and macrophage proliferation, involved in mesangial cell proliferation and in the establishment of experimental nephritis. Elevated serum concentrations of M-CSF mark and herald the onset of lupus nephritis.

Objectives To investigate M-CSF expression in patients with AAV with and without renal involvement.

Methods Upon informed consent, plasma samples from 29 patients with AAV (18 granulomatosis with polyangiitis, GPA, 6 eosinophilic granulomatosis with polyangiitis, EGPA, and 5 microscopic polyangiitis, MPA) and 10 healthy controls were collected, together with data regarding clinical history, disease activity (as estimated by the Birmingham Vasculitis Activity Score, BVAS) at the time of venepuncture and routine laboratory parameters. M-CSF plasma concentration was assessed by using a commercial ELISA assay. Data are expressed as mean ± standard error of mean.

Results Higher levels of M-CSF were detected in patients with AAV in comparison to controls (453.45±78.14 vs 117.58±14.24 pg/ml; p=0.017). Differences between AAV types were not significant. M-CSF levels correlated positively with the BVAS (p=0.010). Positive correlations were also identified among M-CSF, serum C-reactive protein (p<0.001) and erythrocyte sedimentation rate (p=0.022), while haemoglobin correlated inversely with M-CSF (p=0.012). Patients with active renal disease had significantly higher levels of M-CSF when compared to patients with active disease and no kidney involvement, with patients in remission with or without a history of renal involvement and with healthy controls (p=0.001; p=0.019; p=0.016; p<0.001 respectively). M-CSF levels did not differ between ANCA-positive/negative patients and were not associated with the involvement of other organs.

Conclusions M-CSF is higher in patients with AAV and active nephritis and could contribute to the pathogenesis of these diseases. In addition, M-CSF could represent a marker of renal involvement in AAV.

References

1. Luqmani RA. Frontiers Immunol. 2014

2. Hamilton TA et al. Front Immunol. 2014

3. Menke J et al. J Am Soc Nephrol. 2014

Disclosure of Interest None declared