Granulocytes and B cells decrease in bone marrow upon antibiotic therapy, whereas T cells increase. Mature blood cells in bone marrow of control (Ctrl) vs antibiotic-treated (Abx) mice were quantified by flow cytometry, including (A) granulocytes, (B) B cells, (C) T cells, (D) CD4⁺ T cells, and (E) CD8⁺ T cells. (F) The CD4:CD8 ratio was calculated based on percentages of each population. (G) Regulatory T cells (Treg) were quantified by flow cytometry. Results are compiled from 2 to 4 independent experiments (n = 9-17 per group). Graphs show mean + SEM, with statistical significance determined by Student t test. *P < .05, ***P < .001.