Reversible Microbial Colonization of Germ-Free Mice Reveals the Dynamics of IgA Immune Responses

TLDR

The adult mammalian lower intestine is densely colonized by nonpathogenic microbes that induce protective immune responses, yet the continuous presence of commensals has made studying mucosal immune dynamics difficult. The study aims to establish a reversible germ‑free colonization system in mice independent of diet or antibiotics. The system allows controlled colonization of germ‑free mice without dietary or antibiotic manipulation. In germ‑free mice, a slow (>14 days) onset of a long‑lived (half‑life >16 weeks) highly specific anti‑commensal IgA response was observed, which was rapidly abrogated by ongoing commensal exposure; sequential doses did not produce a classic prime‑boost effect, but IgA induction occurred stepwise, matching the current bacterial repertoire.

Abstract

The lower intestine of adult mammals is densely colonized with nonpathogenic (commensal) microbes. Gut bacteria induce protective immune responses, which ensure host-microbial mutualism. The continuous presence of commensal intestinal bacteria has made it difficult to study mucosal immune dynamics. Here, we report a reversible germ-free colonization system in mice that is independent of diet or antibiotic manipulation. A slow (more than 14 days) onset of a long-lived (half-life over 16 weeks), highly specific anticommensal immunoglobulin A (IgA) response in germ-free mice was observed. Ongoing commensal exposure in colonized mice rapidly abrogated this response. Sequential doses lacked a classical prime-boost effect seen in systemic vaccination, but specific IgA induction occurred as a stepwise response to current bacterial exposure, such that the antibody repertoire matched the existing commensal content.