Cellular Immune responses during latent tuberculosis : immunodiagnosis and correlates of protection

Abstract

This thesis focuses on cellular immunity against mycobacteria during latency with the aim to contribute to improved immunodiagnosis of latent TB and to gain insight into immune responses which play a role in controlling latent infection. Several new highly M. tuberculosis-specific peptides mixtures were identified to optimize the sensitivity of immunodiagnostic assays. The performance of interferon-gamma-release-assays (IGRA) for detection of latent TB were evaluated. Two short-incubation IGRA, QuantiFERON-TB Gold and T-SPOTTM.TB, were found to correlate better to the level of exposure to M. tuberculosis than the tuberculin skin test (TST), indicating that these assays are very sensitive for detection of recent infections. However, short-incubation IGRA are less sensitive than prolonged-incubation IGRA and TST for detection of latent TB acquired in the past. The search for proteins that are specifically targeted by the immune system during latency led to the identification of several antigens encoded within the DosR-regulon. This set of genes of M. tuberculosis is strongly upregulated by during in vitro models of latency. These antigens, including 16kDa _-crystallin, were preferentially recognized by latently infected individuals, which suggest that T-cell responses to latency antigens are associated with natural protection against reactivation of TB, warranting their further study as vaccine candidates.