The interplay of protein secretion and lipid virulence factors in host immune suppression by Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) infects one-quarter of the global population and causes more deaths annually than any other infectious disease. Despite triggering a strong immune response, Mtb evades and suppresses host immunity, establishing chronic infection. Two critical virulence factors, the ESX-1 type VII secretion system and the mycomembrane lipid phthiocerol dimycocerosate (PDIM), play a key role in this immune modulation, but their precise mechanisms remain unclear. Recent data suggest that ESX-1 and PDIM may functionally intersect, as mutants in these pathways exhibit similar virulence phenotypes. This proposal aims to investigate whether ESX-1 and PDIM operate within the same virulence pathway and how PDIM influences ESX-1. Additionally, we will explore whether their roles in virulence involve suppression of protective Th17 CD4 T cell responses and induction of immunosuppressive type I interferons (IFNs). Aim 1 will test whether ESX-1 and PDIM exhibit epistasis for virulence in mice and define how PDIM impacts ESX-1 function. We hypothesize that PDIM mutants subtly affect ESX-1 activity, which will be tested through epistasis experiments and proteomic profiling of ESX-1 function in PDIM mutants. Aim 2 will investigate whether blocking IL-23 explains the suppression of Th17 differentiation by ESX-1/PDIM mutants. We have shown that these mutants induce higher IL-23 production and a robust Th17 response, suggesting that ESX-1 and PDIM suppress this protective response. We will test the role of IL-23 suppression in Th17 differentiation and perform epistasis testing for CD4 T cell orchestration. Aim 3 will determine whether type I IFN induction is necessary for the virulence of ESX-1 and PDIM mutants. Both factors induce type I IFN, which impairs host responses to Mtb. We will test if type I IFN induction is critical for virulence by evaluating mutant strains in mice lacking type I IFN signaling. These studies will provide valuable insights into Mtb's immune evasion strategies, potentially leading to new therapeutic interventions. Project Number: 1R01AI197387-01 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: Sarah Stanley | Institution: UNIVERSITY OF CALIFORNIA BERKELEY, BERKELEY, CA | Award Amount: $756,714 | Activity Code: R01 | Study Section: Special Emphasis Panel[ZRG1 IIDA-B (02)] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R01AI19738701