A. Acetate (open triangles), Propionate (closed circles) and butyrate (open boxes) are present in BAL. Concentrations are corrected for BAL induced dilution of epithelial lining fluid (ELF). Propionate is significantly elevated in HIV-infected subjects, Mann–Whitney U test. B. In HIV infected individuals with paired samples, ELF SCFA is higher than serum in all subjects, with a median ratio of 370. C. Addition of PPD to BAL cells demonstrates induction of FoxP3 CD4+ cells significantly correlates with in vivo ELF acetate or propionate at the time of bronchoscopy, Spearman correlation.