Serum levels of the metabolic markers C-peptide and 5-HT and the immune markers IL-5, IL-10, and MCP-1 of (A) erythromycin-treated and control mice (n = 9 for both groups), (B) germ-free mice and germ-free mice receiving erythromycin treatment (n = 7 per group), and (C) germ-free mice colonized with erythromycin-associated or control microbiota (n = 9 per group). Serum biomarkers were assessed at the end of the 90-day study. Statistical comparisons were performed using an unpaired t test, and significance is set at P < 0.05.