Plasma interleukin-18 levels are a biomarker of innate immune responses that predict and characterize tuberculosis-associated immune reconstitution inflammatory syndrome.

BACKGROUND Tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) is a substantial problem in HIV/TB coinfected patients commencing antiretroviral therapy (ART). The immunopathogenesis of TB-IRIS includes increased production of proinflammatory chemokines and cytokines, including interleukin-18, which is a signature cytokine of the nucleotide-binding domain and leucine-rich repeat pyrin containing protein-3 inflammasome. We compared plasma levels of interleukin-18 and other biomarkers of monocyte/macrophage activation in the prediction and characterization of TB-IRIS. METHODS Biomarkers were assayed pre-ART and during TB-IRIS, or equivalent time-point, in a case-control study of Malaysian HIV patients with paradoxical or unmasking TB-IRIS (n = 15), TB no IRIS (n = 14), and no TB or IRIS (n = 15). Findings for interleukin-18 were verified in another cohort of patients with paradoxical TB-IRIS (n = 26) and their controls (n = 22) from India. RESULTS Interleukin-18 was higher in TB-IRIS patients pre-ART and during the event in both Malaysian patients (P < 0.0001) and Indian patients (P < 0.01). CXCL10 was higher pre-ART (P < 0.001), mainly in paradoxical TB-IRIS patients, and during TB-IRIS (P < 0.001), whereas CXCL8 was only higher during TB-IRIS (P < 0.001). Soluble(s) CD14 was increased in all patients with HIV/TB coinfection pre-ART and during TB-IRIS or equivalent time-point, compared with patients without TB. In contrast, interferon-γ was lower before and during TB-IRIS. By receiver operating curve analysis, CXCL10, and/or interleukin-18 pre-ART were predictive of TB-IRIS. CONCLUSION Plasma interleukin-18 levels pre-ART are candidate biomarkers for predicting paradoxical and unmasking TB-IRIS and should be investigated for risk stratification and elucidation of disease pathogenesis.