Figure 8. OPN acts as an opsonin facilitating phagocytosis by microglia/macrophages.
(a) Triple immunostaining of OPN (green), CD11c (red) and Iba1 (blue) shows that OPN-granules are phagocytosed by microglia/macrophages, which are positive for CD11c in the ventral horn of SOD1G93A mice on P100. (b) The OPN-phagocytosing and CD11c-positive cells are also positive for CD45 in the ventral horn of SOD1G93A mice on P100. (c) Fluorescent microbeads coated with BSA, IgG or OPN were presented to cultured microglia, after which internalization of the beads by the microglia was analyzed and quantified using flow cytometry. BSA-coated and IgG-coated beads were used as negative and positive controls, respectively. Note that phagocytosis of OPN-coated beads was not influenced by prior treatment with anti-CD44 or anti-αv integrin neutralizing antibodies. Scale bar, 20 μm (a). See also Supplemental Fig. 9.