We found patterns of elevated innate inflammatory signaling (colonic Il6, Tnf, and Tlr4) and endotoxemia (circulating LBP) in young germ‐free mice after 4 weeks of colonization with intestinal contents from aged mice compared with young counterparts, thus providing a direct link between aging‐induced shifts in microbiota immunogenicity and host inflammation. Here, IL6 is linked to serum lipopolysaccharide activity.