APOE promotes subretinal macrophage survival via IL-6.Figure 6Quantitative RT-PCR of FasLmRNA normalized with β-actinmRNA of 12-month-old C57BL/6 RPE/choroid plexus 3 h after subretinal injection of PBS (PBS; n = 36), IL-6 (n = 17), and APOE3 (n = 21); calculated intraocular concentrations: 5 ng/ml and 10 μg/ml, respectively; one-way ANOVA/Dunnett post hoc test PBS versus IL-6 *P = 0.038; t-test PBS versus IL-6 *P = 0.043. Mouse IL-6 ELISA of supernatants from C57BL/6J peritoneal macrophages incubated for 24 h in control medium, lipid-free APOE3 (5 μg/ml), APOE3 (5 μg/ml), and polymyxin B (25 μg/ml), heat-denatured APOE3 (dAPOE3, 5 μg/ml), APOE3 (5 μg/ml), and rat IgG1 isotype control (IgG, 100 μg/ml) or APOE3 (5 μg/ml) and rat anti-CD14 antibody (aCD14 Ab, 100 μg/ml) or APOE3 (5 μg/ml) and rat anti-TLR2 antibody (aTLR2 Ab, 100 μg/ml) (n = 5-6/group; one-way ANOVA/Bonferroni multi-comparison tests: APOE3 versus CTL *P < 0.0001; dAPOE3 versus APOE3 #P < 0.0001; APOE3 IgG versus CTL P < 0.0001; APOE3 IgG versus APOE3 aCD14 Ab §P < 0.0001; APOE3 IgG versus APOE3 aTLR2 Ab ++P <0.0001. Mann-Whitney U-test: APOE3 versus CTL *P = 0.0043; dAPOE3 versus APOE3 #P = 0.0117; APOE3 IgG versus CTL P = 0.0080; APOE3 IgG versus APOE3 aCD14 Ab §P = 0.0117; APOE3 IgG versus APOE3 aTLR2 Ab ++P = 0.0079. The experiment was repeated twice with similar results). Quantitative RT-PCR of IL-6mRNA normalized with S26mRNA of C57BL/6J and Cx3cr1GFP/GFP, and Cx3cr1GFP/GFP ApoE−/− peritoneal macrophages cultured for 24 h with CX3CL1 (n = 5 per group, one-way ANOVA/Bonferroni post hoc multi-comparison tests: C57BL/6J versus Cx3cr1GFP/GFP *P < 0.0001 and Cx3cr1GFP/GFP versus Cx3cr1GFP/GFPApoE−/−‡P < 0.0001. Mann-Whitney U-test: C57BL/6J versus Cx3cr1GFP/GFP *P = 0.0079 and Cx3cr1GFP/GFP versus Cx3cr1GFP/GFPApoE−/−‡P = 0.0079. The experiment was repeated twice with similar results.). Orthogonal and lateral Z-stack projection of IL-6 (D, red), IBA-1+ (E, green), and phalloidin (E, blue) of IBA+ mononuclear phagocytes adjacent to the phalloidin+ RPE of a retinal flatmount from a 12-month-old Cx3cr1GFP/GFP mouse. (Representative of three independent experiments, immunostainings omitting the primary antibody served as negative controls). Quantification of subretinal CFSE+F4/80+ macrophages on RPE and retinal flatmounts 24 h after subretinal injection of C57BL/6J CFSE+ macrophages into C57BL/6J with or without IL-6 (n = 15-20/group; calculated intraocular concentrations of 5 ng/ml. Mann-Whitney U-test: *P < 0.0001).Quantification of subretinal CFSE+F4/80+macrophages on RPE and retinal flatmounts 24 h after subretinal injection of Cx3cr1GFP/GFPCFSE+Mϕs into C57BL/6J with control (IgG, n = 16) or anti-IL-6 antibody (aIL-6 Ab, n = 8; calculated intraocular concentrations 5 μg/ml; per group. Mann-Whitney U-test: *P = 0.0036). Graphical summary. 7 day laser-injured IBA-1 (green) and CD102 (red) double-stained RPE flatmounts of control IgG- (I) and anti-IL-6-treated (J) Cx3cr1GFP/GFP mice.Quantification of subretinal IBA-1+ mononuclear phagocytes/impact localized on the lesion surrounding RPE of Cx3cr1GFP/GFP mice treated with control IgG, IL-6-, or CD14-blocking antibodies (calculated intraocular concentration 5 μg/ml; n = 13-14/group, one-way ANOVA/Dunnett's post hoc tests of IgG versus any other group *P < 0.001. Mann-Whitney U-test IgG versus anti-IL-6 *P = 0.0021; IgG versus anti CD14*P = 0.0028).