IgA Dysfunction Induced by Early-Lifetime Low-Dose Antibiotics Exposure Aggravates Diet–Induced Metabolic Syndrome

Background: Low-dose antibiotic contamination in animal feed is a persistent global food safety challenge. Transient early-life exposure to low-dose penicillin (LDP) is known to induce metabolic syndrome (MetS) in adult mice, but the underlying mechanisms are unclear. Introduction: This study investigated the role of gut microbiota (GM) and intestinal immunity in mediating the long-term metabolic effects of early-life LDP exposure. Methods: Mice were exposed to LDP transiently during early life. GM composition was analyzed. Intestinal IgA responses were quantified. Bacterial encroachment, systemic and adipose tissue inflammation, and diet-induced MetS were assessed. Germ-free (GF) mice received GM transplants from LDP-exposed or control mice to test causality and persistence. Results: Early-life LDP exposure significantly disrupted GM composition, particularly in the ileum, in 30-day-old mice. These GM alterations caused persistent suppression of intestinal IgA responses, evidenced by reduced IgA-producing cells and sIgA levels. This suppression was constrained to early-life exposure: transferring LDP-modified GM to GF mice produced only a transient reduction in fecal sIgA. The LDP-induced sIgA reduction decreased IgA binding of bacteria, leading to increased bacterial encroachment and systemic and adipose tissue inflammation. These pathological changes exacerbated diet-induced MetS. Discussion: Our findings demonstrate that early-life LDP exposure induces persistent intestinal IgA deficiency through lasting GM alterations initiated in early development. This deficiency drives bacterial encroachment, inflammation, and ultimately exacerbates MetS. Conclusions: The exacerbation of diet-induced metabolic syndrome by early-life LDP exposure occurs through an intestinal sIgA-dependent pathway triggered by persistent GM disruption. This highlights a critical mechanism linking early-life antibiotic exposure, gut immune dysfunction, and long-term metabolic health, with significant implications for food safety.