IFNA1 and infection: Additionally, Ly6Chi blood monocyte levels significantly increase after antibiotic treatment.23 The results in this study implicate that the microbiome modulates the permissiveness of Ly6Chi monocytes to CHIKV in the blood, which affects viremia at the early stages of infection by downregulating IFN and ISG.23 However, Ly6C expression was upregulated in the blood and intestine after CHIKV infection regardless of antibiotic treatment, with a significant increase in the Abx elderly group that exhibited highly activated intestinal ISGs (Figure 6(b)).