Do Anti-Tuberculous antibiotics or steroid therapy influence cytokine production in Quantiferon-TB gold in Tube-Based immunoassays?

The ability to monitor and confirm adequate treatment of latent tuberculosis (TB) infection would be a major advance. This would allow comparisons of antibiotic regimens and treatment durations, and help reduce transmission from subsequent reactivation following failed therapy. There has been recent interest in using commercial interferon-gamma release assays and other cytokine-based assays to monitor therapy. The potential immunomodulatory effects of therapeutic concentrations of anti-tuberculous drugs or steroids needs to be considered in assessing these assays for monitoring. We determined whether therapeutic concentrations of anti-tuberculous antibiotics or dexamethasone affect IFN-γ production in the QuantiFERON-TB-Gold In-Tube (QFT-IT) assay, as well as a range of other cytokines (TNF-α, IFN-γ, IL-lra, IL-2, IL-10, IL-13, IP-10, MIP-β). Blood was collected from ten adults with latent TB prior to starting preventive therapy. This was added to six sets of QFT-IT tubes containing therapeutic concentrations of isoniazid, rifampicin, isoniazid with rifampicin, ciprofloxacin, dexamethasone or nil. QFT-IT assays were then run according to manufacturer’s instructions. Remaining supernatant was used to measure the additional cytokines by Luminex assay. In four of ten participants the QFT-IT result changed from positive to negative as a result of incubation with antibiotics and/or dexamethasone. The greatest reduction in IFN-γ responses occurred with dexamethasone.