Refining cytokine signatures: flow cytometry-based differentiation between TB infection and disease.

BACKGROUND

Distinguishing TB infection (TBI) from TB disease remains difficult because routine tests, including tuberculin skin test and interferon-gamma release assay (IGRA), cannot separate these states. We assessed a flow cytometry-based assay that measures T-cell cytokine responses after stimulation with Mycobacterium tuberculosis.

METHODS

We enrolled 118 IGRA-positive participants, including individuals with TB/TBI. Individuals were grouped by age and disease category into paediatric/adult TB, TBI, and immunocompromised TBI. Peripheral blood lymphocytes were stimulated with ESAT-6/CFP-10 antigens under CD4+-focused (TB1) or combined CD4+/CD8+ (TB2) conditions. Intracellular IL-10, IL-2, and tumour necrosis factor-α (TNF-α) were quantified by flow cytometry. Cytokine levels were compared using Mann-Whitney U tests.

RESULTS

Among children, most cytokine responses overlapped between TBI and TB, except TNF-α in CD8+ T cells after TB2 stimulation, which was higher in TB. In adults, IL-10 in CD4+ T cells was elevated in TBI after TB1 and TB2 stimulation, whereas IL-2 in CD4+ T cells was higher in TB after TB2 stimulation. TNF-α did not differentiate groups in adults.

CONCLUSION

Flow-cytometric cytokine profiling may help distinguish TBI from TB, with age-specific markers. TNF-α in CD8+ T cells appears informative in children, while IL-10 and IL-2 in CD4+ T cells show promise in adults. Further validation is needed.