Fig. 1

Infectious environment accelerates neurodegeneration in frontal cortex of AD mice. Wt and 5xFAD mice were grown in either naturally bred (so called “dirty”) environment or SPF environment. Mice were sacrificed at two timepoints for pathological assessment. A In wild type mice there was no loss of cortical neurons at age 7 months, whether grown in an SPF or in a naturally bred, non-SPF facility. 5xFAD mice grown in a non-SPF environment exhibited earlier and accelerated neurodegeneration as compared to 5xFAD mice grown in a SPF-facility, evident already at age 7 months. B–E Representative images of the cortex (at Bregma 0.0 ± 0.1 mm) stained for NeuN + neurons. B 7-month WT mice in an SPF environment. C 7-month WT mice in a non-SPF environment. D 7-month 5xFAD transgenic mice in a SPF environment. E 7-month 5xFAD transgenic mice in a non-SPF environment. F At age 1 year, there was a reduction of cortical neuron density in both 5xFAD groups compared to wt, with no further contribution of environmental conditions. G–H Representative images of the cortex stained for Iba1 + microglia and amyloid-beta plaques in wt and 5xFAD transgenic mice age 7 months. I Amyloid plaques were found only in transgenic mice, with no significant difference between SPF and non-SPF groups. J 5xFAD mice exhibited three- to fourfold increase in microglial density as compared with Wt mice and no difference between those housed in non-SPF versus SPF conditions. Error bars-SEM. P values by students unpaired T test in I and one-way analysis of variance (ANOVA) followed by Tukey’s post-hoc test in A, F, I: #P = 0.06, *P < 0.05, **P < 0.01, ***P < 0.001. n = 5–6, excluding 7-month non-SPF 5xFAD in which n = 4