Minimal immune cell subset differences in a cohort of close contacts of tuberculosis index cases

Understanding the perturbations in immune response across the spectrum of TB infection is still unclear. Here, we followed close contacts of pulmonary TB patients with serial QFT testing at 0, 3, 6, and 12 months, and stratified them into six subgroups: QFT-increasing (low/high), QFT-converters (QFT-to QFT+), QFT + stable, and QFT-individuals. Despite these distinct QFT trajectories, we observed minimal differences in immune cell frequencies, activation profiles, and T-helper subset distributions among QFT subgroups, suggesting limited immunological stratification based on QFT dynamics. Ex vivo immune phenotyping, including CD4, CD8, NKT cell frequencies, memory T-cell subsets, and activated T-cells (HLA-DR⁺CD38⁺), failed to distinguish between QFT subgroups, suggesting blood-based immune profiling may not capture subtle immunological transitions among different QFT subgroups. Active TB (ATB) patients showed marked immune alterations, with elevated antigen-specific CD4 T-cells, activated T cells, intermediate monocytes, NK cells at-diagnosis, which declined following treatment, indicating immune recovery. This suggest, while ex vivo immune profiling effectively distinguishes ATB from non-diseased states, it lacks the sensitivity to resolve QFT-based subgroups. Findings suggest either immune similarity among close contacts regardless of QFT status or limits of blood-based profiling in detecting early changes, underscoring the difficulty of distinguishing QFT subgroups with conventional ex vivo approaches.