Vitamin A derivative reshapes immune response to drug‑resistant TB

Tuberculosis (TB), caused by Mycobacterium tuberculosis ( M.tb ), remains a top infectious killer worldwide, and the rise of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains has made treatment increasingly difficult. To explore alternatives that boost the host immune system rather than directly targeting bacteria, Indrakant K. Singh and team investigated All-trans retinoic acid (ATRA), an active vitamin A metabolite known for immunomodulatory effects. The researchers focused on how ATRA changes the global transcriptional state of macrophages—key immune cells that host and fight M.tb—when infected with strains that differ in drug resistance. Using murine peritoneal macrophages infected with the drug-susceptible H37Rv, MDR-2261, or XDR-MCY strains, they compared cells treated with or without ATRA. The study combined genome-wide RNA sequencing with targeted validation by RT-PCR and flow cytometry to map how infection and ATRA treatment rewire macrophage gene expression. By profiling these different infection states side-by-side, Singh’s team aimed to reveal whether ATRA can recalibrate macrophage defenses against drug-resistant TB and identify strain-specific vulnerabilities.

The core experimental approach was RNA sequencing of murine peritoneal macrophages infected with H37Rv, MDR-2261, or XDR-MCY, validated by RT-PCR and flow cytometry. Across all three M.tb strains the macrophages mounted a conserved pro-inflammatory program marked by induction of Nos2, Il1b, and Acod1, coupled with progressive suppression of host translational and mitochondrial machinery. However, XDR-MCY showed unique signatures: it induced Ifnb1 /IFN-β, suppressed antioxidant genes Prdx1 and Gpx4 (with Gpx4 suppression also seen in MDR-2261), and selectively downregulated MHC-II processing genes, suggesting layered immune evasion. Treatment with All-trans retinoic acid (ATRA) activated canonical retinoid signaling in every infection state and consistently induced Arg1-mediated resolution signaling. Notably, ATRA suppressed Nos2 in H37Rv- and MDR-2261-infected macrophages and selectively restored Epas1 /HIF-2α in those same infections without disrupting the HIF-1α-driven antimicrobial program or itaconate biosynthesis. Importantly, ATRA responsiveness diminished with increasing drug resistance: XDR-MCY-infected macrophages were largely refractory to transcriptional reprogramming by ATRA.

These results give a transcriptional rationale for considering All-trans retinoic acid (ATRA) as a host-directed adjunct in drug-resistant TB, while highlighting limits and new targets for study. The finding that ATRA can recalibrate inflammatory and resolution pathways—inducing Arg1 and restoring Epas1 /HIF-2α in H37Rv and MDR-2261 infections without impairing HIF-1α-driven antimicrobial programs or itaconate production—suggests it could bolster protective macrophage functions alongside antibiotics. Conversely, the unique behaviors of XDR-MCY, including induction of Ifnb1 /IFN-β, suppression of Prdx1 and Gpx4, and downregulation of MHC-II processing genes, point to mechanisms by which some drug-resistant strains evade host control and resist reprogramming. The shared suppression of Gpx4 in drug-resistant strains and the XDR-specific Ifnb1 signature emerge as vulnerabilities that warrant deeper investigation. Overall, this work suggests ATRA’s benefits may be strain-specific and that carefully targeted host-directed strategies, informed by transcriptional profiling, will be needed to tackle MDR and XDR TB.