Figure 2.

Immature microglia phenotype under germ‐free (GF) conditions. Mice raised under conventional (specific pathogen‐free; SPF) conditions exhibit mature microglia with ramified morphology that respect territorial boundaries (SPF; left). Microglia from GF mice (right) display a hyper‐ramified morphology, increased cell density accompanied by increased proliferation rate, up‐regulation of colony‐stimulating factor 1 receptor (CSF‐1R), F4/80 and CD31 and a changed gene expression profile more related to that of immature cells. Eradication of host microbiota with antibiotics, the presence of a gut flora with strongly limited diversity or FFAR2‐deficiency in the host are causing a microglial phenotype similar to that observed in GF mice, whereas recolonization with a highly diverse gut flora or the application of SCFA is able to re‐establish a mature microglial phenotype.