IL-24 modulates IFN-γ expression in patients with tuberculosis

IL-24 is a newly described member of the IL-10 family. We previously demonstrated that PBMC from TB patients exhibited low levels of IL-24 and IFN-γ compared to subjects with latent tuberculosis infection (LTBI). In order to investigate the role of IL-24 in IFN-γ expression in TB patients, we stimulated PBMC from individuals with LTBI or TB patients with the Mtb-specific antigen, early secretory antigenic target-6 (ESAT-6) and measured cytokine expression using quantitative real-time PCR (qPCR). Exogenous IL-24 increased IFN-γ expression in PBMC obtained from TB patients while neutralization of IL-24 reduced IFN-γ expression in PBMC from subjects with LTBI. Exogenous IL-24 enhanced IFN-γ expression by increasing expression of IL-12 family cytokines, including IL-12α, IL-12β, IL-23α and IL-27, and by reducing FOXP3 expression in PBMC from TB patients. This is the first demonstration that IL-24 may play an important role in IFN-γ expression following infection with Mtb.