To compare the effect of a global lifetime C5aR1 genetic ablation with pharmacological inhibition of C5aR1in adult mice, we explored the effects of systemic C5aR1 inhibition on the bacterial communities of the gut via treatment with the C5aR1 antagonist, PMX205, for 12 weeks, in wild-type mice and during the onset of AD pathology in AD model mice. This evidence concerns the gene C5AR1 and Alzheimer disease.