Fig. 7: C4a and C4b can facilitate the astrocytic engulfment of microglial debris in vivo and in vitro.

a C4a and C4b restore the astrocytic engulfment of microglial debris in vitro in serum-free culture medium. b Quantifications of the phagocytic influence by complement supplementation and preopsonization in serum-free culture medium. N = 11 independent biological replicates of each group. One-way ANOVA with Holm‒Sidak’s multiple comparisons test (post hoc). c Scheme of in vivo microglial depletion and time points for analysis. d Reanalysis of RNA-seq data from whole-brain homogenate (GSE108269²⁷) showing that Gfap and C4b are upregulated and C1qa is downregulated during microglial ablation, whereas C2, C3 and C4a remain at low levels and are unaffected. N = 5 mice at D0 and N = 4 mice at D2 to D21. One-way ANOVA with Holm‒Sidak’s multiple comparisons test (post hoc). e qPCR further confirmed the upregulation of C4b in sorted astrocytes upon microglial depletion. N = 5 in each group. Two-tailed independent t test. f Scheme of the in vivo examination of astrocytic engulfment using AAV PHP.eB-based astrocyte labeling and microglial depletion. g Confocal orthogonal colocalization and 3D reconstruction show that C4b^−/− impairs the astrocytic engulfment of microglial debris under physiological condition (D21) and upon CSF1R inhibition (D23). h Quantification of microglial debris engulfment by astrocytes. N = 7 (D21) and 8 (D23) WT mice, and N = 3 (D21) and 5 (D23) C4b^−/− mice. One-way ANOVA with Holm‒Sidak’s multiple comparisons test (post hoc). PLX5622 PLX5622-formulated AIN-76A diet, CD control AIN-76A diet, IV intravenous, MFI mean fluorescence intensity, Ctx cortex, Hipp hippocampus, OB olfactory bulb. Data are presented as mean ± SD. The source data are provided as a Source Data file.