High IL-6 and low IL-15 levels mark the presence of TB infection: A preliminary study

- High IL-6, high IFN-γ and low IL-15 levels suggest active tuberculosis.
- Elevated IL-6 and IFN-γ levels discriminate active from latent TB infection.
- Low IL-15 levels indicate an exposure to Mycobacterium tuberculosis.
- Cytokine profile is a more effective biomarker than a single cytokine in discriminating mycobacterial infection.

The host immune response, apart from mycobacterial factors, is a significant determinant in the development of tuberculosis (TB). The purpose of the study was to examine whether the differential serum profiles of cytokines IL-1β, IL-2, IL-4, IL-6, IL-10, IL-15, IFN-γ, TGF-β, and TNF-α could discriminate between TB patients and healthy controls and provide insights into pathogenesis. Serum samples from TB patients, TB patient contacts and healthy controls were collected and analyzed by ELISA. The cytokine concentrations obtained were stratified into three groups: below detection limit (BDL), low values, and high values. The differences in cytokine concentrations were analyzed by Fisher's exact test. The statistically significant results were interpreted based on post-hoc analysis of the chi square contingency table using the adjusted residual method. Among the assayed cytokines, there was a statistically significant difference in the detection levels of IL-6, IL-15 and IFN-γ. Levels of IL-1β, IL-2, IL-4, IL-10, TGF-β and TNF-α did not vary. Post-hoc analysis of the significant results revealed that dynamic changes in the BDL and high values of cytokines influenced the post-infection cytokine milieu in the study subjects. The study concludes that altered balance in the levels of serum cytokines can be indicative of TB pathogenesis. Hence, profiling of dynamic changes in cytokines would facilitate effective TB diagnostic and treatment strategies.