Differences in T cell immune responses to novel Mycobacterium tuberculosis antigens (PPE68, PE9, and IrtA) in tuberculosis patients in southern Thailand.

Tuberculosis (TB) continues to pose a significant public health challenge. An effective immune response against Mycobacterium tuberculosis (M.tb) is widely dependent on T cell memory responses, particularly in Latent tuberculosis infection (LTBI) and active tuberculosis disease (ATB). We quantified and phenotypically characterized peripheral blood mononuclear cells (PBMCs) from Southern Thai cohort after stimulation with established M.tb specific antigen: PPD and novel antigens: IrtA, PE9 and PPE68. We compared immune responses in 60 individuals (ATB n = 20, LTBI n = 20 and healthy controls (HC) n = 20) using flow cytometry and Enzyme linked Immunospot (ELISpot) assays. PPD induced the strongest IFN-γ responses across all groups. PPE68 demonstrated the highest immunogenicity among the novel antigens, inducing stronger IFN-γ responses. PE9 uniquely distinguished disease states by showing significantly reduced CD4+ TNF-α production in ATB and LTBI. PD-1 expression was markedly elevated on PPD-stimulated CD4+ T cells in ATB and LTBI, reflecting antigen load, T cell activation and/or exhaustion, whereas PE9 induced higher PD-1 expression in HC. These findings highlight the distinct immune signatures elicited by classical and novel M.tb antigens, which support further evaluation for future diagnostic or biomarker applications.