In a TB patient trial, adding phenylbutyrate (500 mg twice daily) and high‑dose vitamin D3 (5,000 IU daily) for eight weeks boosted the body’s natural antimicrobial peptide LL‑37, reduced several inflammatory signals, and increased a cell‑clean‑up process called autophagy, helping patients recover faster. The findings show these supplements can modulate the immune system, but the study was limited to sick adults and didn’t test healthy people.

We have previously shown that 8 weeks' treatment with phenylbutyrate (PBA) (500mgx2/day) with or without vitamin D₃ (vitD₃) (5000 IU/day) as host-directed therapy (HDT) accelerated clinical recovery, sputum culture conversion and increased expression of cathelicidin LL-37 by immune cells in a randomized, placebo-controlled trial in adults with pulmonary tuberculosis (TB). In this study we further aimed to examine whether HDT with PBA and vitD₃ promoted clinically beneficial immunomodulation to improve treatment outcomes in TB patients. Cytokine concentration was measured in supernatants of peripheral blood mononuclear cells (PBMC) from patients (n = 31/group). Endoplasmic reticulum stress-related genes (GADD34 and XBP1spl) and human beta-defensin-1 (HBD1) gene expression were studied in monocyte-derived-macrophages (MDM) (n = 18/group) from PBMC of patients. Autophagy in MDM (n = 6/group) was evaluated using LC3 expression by confocal microscopy. A significant decline in the concentration of cytokines/chemokines was noted from week 0 to 8 in the PBA-group [TNF-α (β = - 0.34, 95% CI = - 0.68, - 0.003; p = 0.04), CCL11 (β = - 0.19, 95% CI = - 0.36, - 0.03; p = 0.02) and CCL5 (β = - 0.08, 95% CI = - 0.16, 0.002; p = 0.05)] and vitD₃-group [(CCL11 (β = - 0.17, 95% CI = - 0.34, - 0.001; p = 0.04), CXCL10 (β = - 0.38, 95% CI = - 0.77, 0.003; p = 0.05) and PDGF-β (β = - 0.16, 95% CI = - 0.31, 0.002; p = 0.05)] compared to placebo. Both PBA- and vitD₃-groups showed a decline in XBP1spl mRNA on week 8 (p < 0.03). All treatment groups demonstrated increased LC3 expression in MDM compared to placebo over time (p < 0.037). The use of PBA and vitD₃ as adjunct therapy to standard TB treatment promoted favorable immunomodulation to improve treatment outcomes. This trial was retrospectively registered in clinicaltrials.gov, under identifier NCT01580007 .