MBP binds to the extracellular surface of neuronal plasma membrane.

<p>(A) Neurons were incubated with HBSS, 10 µg/mL or 50 µg/mL MBP for 5 min, and washed for three times with HBSS, 5 min each time. The cells were fixed in 4% paraformaldehyde without permeabilization and stained for surface-bound MBP on plasma membrane (green). Nuclei were indicated by DAPI (blue). General morphology of neurons was observed by differential interference contrast (DIC) microscopy. MBP was shown to bind to the extracellular surface on both soma (arrowheads) and neurites (arrows). Scale bar, 50 µm. (B) Primary astrocytes, microglia, oligodendrocytes and the endothelial cell line bEND.3 were incubated with HBSS or 50 µg/mL MBP for 30 min, washed with HBSS for three times, 5 min each time, and then stained for MBP surface binding (without permeabilization). No surface-bound MBP was detected (green). GFAP and CD11b were used as markers of astrocytes and microglia, respectively (red). Scale bar, 50 µm. (C) Primary microglia were incubated with 50 µg/mL MBP for the indicated times and the intracellular distribution of MBP was shown by staining with permeabilization (green). Iba1 (red) was used as a microglial marker. Scale bar, 50 µm. Similar results were obtained in three independent experiments.