Early Specific Host Response Associated with Starting Effective Tuberculosis Treatment in an Infection Controlled Placebo Controlled Mouse Study

Recently we proposed exploring the potential of treatment stimulated testing as diagnostic method for tuberculosis (TB). An infection controlled placebo controlled mouse study was performed to investigate whether serum cytokine levels changed measurably during the early phase of TB chemotherapy. Serum was collected prior to and during the first 3 weeks of isoniazid (INH) and rifampicin (RIF) chemotherapy, and levels of 23 selected cytokines/chemokines were measured using a liquid bead array. The serum levels of IFNγ, IP-10, MIG, MCP-1, IL-17 and IL-6 were elevated in the TB infected mice compared to non-infected mice at least at 1 time point measured. In infected mice, IFNγ, IP-10, MIG and MCP-1 levels decreased within 7 days of treatment with RIF+INH compared to placebo. Treatment of non-infected mice in the absence of tuberculosis infection had no effect on these cytokines. IL-17 and IL-6 had decreased to baseline in all infected mice prior to the initiation of treatment. This study demonstrates that systemic levels of some cytokines, more specifically IFNγ, IP-10, MIG and MCP-1, rapidly and specifically change upon starting TB chemotherapy only in the presence of infection in a mouse model. Thus, IFNγ, IP-10, MIG and MCP-1 are promising ‘Treat-to-Test’ targets for the diagnosis of TB and deserve further investigation in a study on human TB suspects.