Simultaneous measurement of antigen-stimulated interleukin-1 beta and gamma interferon production enhances test sensitivity for the detection of Mycobacterium bovis infection in cattle

In order to identify cytokines that may be useful as candidates for inclusion in diagnostic tests for Mycobacterium bovis infection in cattle, we compared the levels of gamma interferon (IFN-γ), interleukin 1β (IL-1β), IL-4, IL-10, IL-12, macrophage inflammatory protein 1β (MIP-1β), and tumor necrosis factor alpha (TNF-α) in whole-blood cultures from tuberculosis (TB) reactor animals or TB-free controls following stimulation with M. bovis-specific antigens (purified protein derivative from M. bovis [PPD-B] or ESAT-6/CFP-10). In addition to IFN-γ responses, the production of IL-1β and TNF-α was also statistically significantly elevated in TB reactor cattle over that in uninfected controls following stimulation with PPD-B or ESAT-6/CFP-10 peptides. Thus, we evaluated whether the use of these two additional readouts could disclose further animals not detected by measuring IFN-γ alone. To this end, receiver operating characteristic (ROC) analyses were performed to define diagnostic cutoffs for positivity for TNF-α and IL-1β. These results revealed that for ESAT-6/CFP-10-induced responses, the use of all three readouts (IFN-γ, TNF-α, and IL-1β) in parallel increased the sensitivity of detection of M. bovis-infected animals by 11% but also resulted in a specificity decrease of 14%. However, applying only IFN-γ and IL-1β in parallel resulted in a 5% increase in sensitivity without the corresponding loss of specificity. The results for PPD-B-induced responses were similar, although the loss of specificity was more pronounced, even when only IFN-γ and IL-1β were used as readout systems. In conclusion, we have demonstrated that the use of an additional readout system, such as IL-1β, can potentially complement IFN-γ by increasing overall test sensitivity for the detection of M. bovis infection in cattle.