Deep immunophenotyping of peripheral blood cells in individuals exposed to Mycobacterium tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is a worldwide public health issue. To control TB, we need prognostic tests to discriminate subjects infected but unlikely to succumb to disease (LTBI) from subjects developing disease (subclinical TB). To address this, we proposed that immunophenotyping could group LTBI from subclinical TB. We reasoned that in a high incidence, low exposure setting such as Leicester we would have a population of people wherein the immune response reflected the state of infection rather than the state of recent exposure to Mtb antigens. We therefore locally recruited 46 subjects designated as healthy unexposed (HC), active TB patients (ATB) or people with evidence of exposure but no clinical symptoms (latent tuberculosis infection, LTBI). We hypothesized that we could separate HC from ATB and that LTBI would be variable, reflecting the broad nature of the LTBI grouping. We compared the frequencies of specific cell types in peripheral blood mononuclear cells both ex vivo and post antigen-specific stimulation between these groups. We also compared the expression of inflammatory cytokines in plasma from the subjects. We developed an ELISA to determine the level of a novel biomarker of active TB, △TM-IL-12Rβ1. We found some individual characteristics were different for the ATB group compared to the other groups with more regulatory and antigen-specific T cells and fewer naïve CD4 T and NK cells. Principal component analysis showed that HC and ATB subjects could be grouped, while LTBI subjects were spread over the HC and ATB grouping. We have established a set of markers that can be used to group HC and ATB, we can now propose a longer follow up study to see whether any combination of these markers is an indicator of progression from latent to active TB.</p