Macrophage colony-stimulating factor receptor/CD115+ non-classical monocytes are expanded in systemic lupus erythematosus and associated with lupus nephritis

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Objective In systemic lupus erythematosus (SLE), the non-classical monocyte compartment is expanded, but its phenotype and association with clinical disease manifestations have not been explored. Method Monocyte subsets from 39 SLE patients, 32 healthy age-matched controls, and 16 patients from a disease control (autoimmune connective tissue disease other than SLE) were determined based on CD14 and CD16 surface expression. Cell surface expression of the receptors for macrophage colony-stimulating factor (M-CSF) (CD115) and granulocyte–macrophage colony-stimulating factor (GM-CSF) (CD116), as well as 6-Sulpho LacNAc (slan), were analysed by flow cytometry. The association of monocyte populations with disease manifestations, disease activity markers, and current medication of each patient was analysed by chart review. Results Non-classical monocytes displayed a cell-type specific signature of high M-CSF receptor CD115 and low GM-CSF receptor CD116 expression that separated them from the other two monocyte subsets. In healthy individuals, the M-CSF receptor on non-classical monocytes was an age-dependent surface marker, with lower expression in young adults. However, SLE monocytes were characterized by a marked expansion of M-CSF receptor/CD115+ non-classical monocytes in patients of all ages. The expanded population of M-CSF receptor/CD115+ non-classical monocytes was associated with lupus nephritis but not with disease activity, and coexpressed slan. Conclusion The non-classical monocyte subset in SLE is characterized by an expansion of M-CSF receptor/CD115+ cells that are associated with lupus nephritis and coexpress slan.