Schwann cells express the macrophage mannose receptor and MHC class II. Do they have a role in antigen presentation?

The mannose receptor (MR) is a transmembrane glycoprotein, postulated to be a link between innate and adaptive immunity. MR is expressed in several cell types but no information is available on that for Schwann cells (SC). We show that rodent SC in primary cultures take up the MR ligand mannosyl/bovine serum albumin-fluorescein isothiocyanate (man/BSA-FITC) in a highly specific manner and bind an antibody against the C-terminus of the murine macrophage MR (anti-cMR). After incubation with man/BSA-FITC, flow cytometry demonstrates 90% positive SC, a dose-dependent increase in tagged cellular components and near total inhibition of the neoglycoprotein uptake by d-mannose or by the mannosylated protein horseradish peroxidase (HRP). Western blot for MR shows that SC share a unique protein of about 180 kDa with peritoneal resident macrophages. Treatment of cultured SC with interferon-gamma (IFN-gamma) or dexamethasone (DM) followed by the addition of man/BSA-FITC and analysis by flow cytometry shows down- or upregulation, respectively, of man/BSA-FITC uptake. Our results show that SC express the MR in a prospectively functional state and suggest an antigen-presenting function of SC, compatible with a role in infectious/inflammatory states of the peripheral nervous system.