Immune responses to latent tuberculosis antigen Rv2659c in Chinese populations.

BACKGROUND The latency-associated antigen Rv2659c is a starvation-related protein of Mycobacterium tuberculosis (M. tuberculosis). It has potential use in tuberculosis (TB) control, but its immunological characteristics in Chinese populations are unclear. METHODS In this study, immunological characteristics and potential diagnostic use of recombinant Rv2659c protein were assessed. Interferon-γ (IFN-γ) production from peripheral blood mononuclear cells (PBMC) was assayed by enzyme-linked immunospot (ELISPOT) in TB patients (80 cases), individuals who were purified protein derivative (PPD)-positive after Bacillus Calmette-Guérin (BCG) vaccination (27 cases), nontuberculous respiratory disease patients (30 cases), individuals who were identified by standard techniques as having latent TB infection (LTBI) (37 cases), and uninfected healthy individuals (75 cases). Serum immunoglobulin G (IgG) levels were assayed by enzyme-linked immunosorbent assay (ELISA) in TB patients (43 cases), LTBI individuals (36 cases) and uninfected healthy individuals (66 cases). RESULTS When stimulated by rRv2659c, PBMC from LTBI individuals gave ELISPOT counts that were significantly higher than those from TB patients, BCG vaccinated individuals, non-TB respiratory disease patients and uninfected healthy individuals (p < 0.05). The rRv2659c stimulation gave detectable IFN-γ production in a higher proportion of persons with LTBI compared with TB patients and uninfected healthy individuals. BCG vaccination and non-TB respiratory disease had little influence on the PBMC response to rRv2659c. The levels of serum IgG specific for rRv2659c were not significantly different between LTBI individuals and TB patients (p > 0.05). CONCLUSION These results suggest that rRv2659c has potential for the diagnosis of LTBI. This is the first clinical report of human immune recognition of Rv2659c in Chinese populations.