Fig. 6

Anti-tau antibodies need the Fc domain to promote tau uptake by microglia. a Flow cytometry analysis of human microglia incubated with fluorescently labelled aggregated tau151–391/4R alone, in the presence tau+AX004/IgG1, or tau+AX004/IgG4, or in the presence of Fab fragment of AX004 showed that antibody-dependent tau uptake required the complete AX004 antibody. Fab fragment of AX004 did not promote uptake of tau (tau+Fab vs tau+AX004/IgG1, ****p < 0.0001, n = 5; tau+Fab vs tau+AX004/IgG4, ***p = 0.0005, n = 5 by one-way ANOVA, Tukey’s multiple comparisons test). Fluorescence intensity of tau positive cells incubated with tau together with Fab was similar to cells incubated with tau alone (tau+Fab vs tau, ns, Tukey’s multiple comparisons test). b Experiment with Fab fragment in mouse microglia confirmed Fc domain requirement in antibody-mediated tau uptake. Fab fragment of DC8E8 did not promote uptake of tau (tau+Fab vs tau, ns, p = 0.8190, n = 8, Tukey’s multiple comparisons test). Pre-incubation of mouse microglia with Fcγ antibodies, anti-FcγI and anti-FcγII/III 1 h before tau uptake confirmed the requirement for the Fc domain. The inhibition of FcγII/III blocked DC8E8-dependent tau uptake (****p < 0.0001, n = 10, by Tukey’s multiple comparisons test). The inhibition of FcγI receptor had no effect on DC8E8-mediated tau uptake (tau+DC8E8/FcgII/III inh vs tau+DC8E8, ns, p > 0.999, n = 10, by Tukey’s multiple comparisons test). For visual clarity, all values were normalized to mean fluorescence values obtained from tau-only wells