Immunogenicity of antigens from the TbD1 region present in M. africanum and missing from modern M. tuberculosis: a cross-sectional study

Background: Currently available tools cannot be used to distinguish between sub-species of the M. tuberculosis complex causing latent tuberculosis (TB) infection. M. africanum causes up to half of TB in West-Africa and its relatively lower progression to disease suggests the presence of a large reservoir of latent infection relative to M. tuberculosis. Methods: We assessed the immunogenicity of the TbD1 region, present in M. africanum and absent from modern M. tuberculosis, in an ELISPOT assay using cells from confirmed M. africanum or M. tuberculosis infected TB patients without HIV infection in the Gambia. Results: Antigens from the TbD1 region induced IFN gamma responses in only 35% patients and did not discriminate between patients infected with M. africanum vs. M. tuberculosis, while PPD induced universally high responses. Conclusions: Further studies will need to assess other antigens unique to M. africanum that may induce discriminatory immune responses.