Mycobacterial-specific secretion of cytokines and chemokines in healthcare workers with apparent resistance to infection with Mycobacterium tuberculosis

BackgroundCurrently, diagnosis of latent TB infection (LTBI) is based on the secretion of IFN-γ in response to Mycobacterium tuberculosis (Mtb) antigens, the absence of which is regarded as no infection. Some individuals appear to resist Mtb infection despite sustained exposure (resisters). In this study, we aimed to assess cytokines, chemokines and antibodies that may be associated with resistance to Mtb infection. We hypothesized that there may be an alternative immune response to Mtb exposure in the absence of IFN-γ in resisters.MethodsWe enrolled HIV-uninfected healthcare workers who had worked in high TB-exposure environments for 5 years or longer. We screened them for LTBI using the tuberculin skin test and the QuantiFERON-TB Gold Plus assay. We performed multiplex Luminex to measure concentrations of T cell-associated cytokines and chemokines as well as total antibodies in plasma collected from unstimulated fresh whole blood and supernatants from QuantiFERON-TB Gold Plus tubes following incubation of whole blood for 16-24 hours with ESAT6/CFP10 peptides.ResultsSamples from 78 individuals were analyzed: 33 resisters (TSTConclusionResistance to Mtb infection despite sustained exposure is associated with lower Mtb-specific secretion of Th1-associated cytokines and chemokines. However, resisters showed secreted concentrations after Mtb stimulation of total antibodies and cytokines/chemokines associated with innate and Th17 immune responses similar to those with Mtb infection. This suggests an ability to mount non-IFN-γ immune responses to Mtb in apparent resisters.