T-cell and serological responses to Erp, an exported Mycobacterium tuberculosis protein, in tuberculosis patients and healthy individuals

BMC Infect Dis. 2007 Jul 26;7:83. doi: 10.1186/1471-2334-7-83.


Background: The identification of antigens able to differentiate tuberculosis (TB) disease from TB infection would be valuable. Cellular and humoral immune responses to Erp (Exported repetitive protein)--a recently identified M. tuberculosis protein--have not yet been investigated in humans and may contribute to this aim.

Methods: We analyzed the cellular and humoral immune responses to Erp, ESAT-6, Ag85B and PPD in TB patients, in BCG+ individuals without infection, BCG+ individuals with latent TB infection (LTBI) and BCG- controls. We used lymphoproliferation, ELISpot IFN-gamma, cytokine production assays and detection of specific human antibodies against recombinant M. tuberculosis proteins.

Results: We included 22 TB patients, 9 BCG+ individuals without TB infection, 7 LTBI and 7 BCG- controls. Erp-specific T cell counts were higher in LTBI than in the other groups. Erp-specific T cell counts were higher in LTBI subjects than TB patients (median positive frequency of 211 SFC/106 PBMC (range 118-2000) for LTBI subjects compared to 80 SFC/106 PBMC (range 50-191), p = 0.019); responses to PPD and ESAT-6 antigens did not differ between these groups. IFN-gamma secretion after Erp stimulation differed between TB patients and LTBI subjects (p = 0.02). Moreover, LTBI subjects but not TB patients or healthy subjects produced IgG3 against Erp.

Conclusion: The frequencies of IFN-gamma-producing specific T cells, the IFN-gamma secretion and the production of IgG3 after Erp stimulation are higher in LTBI subjects than in TB patients, whereas PPD and ESAT-6 are not.

MeSH terms

  • Adult
  • Aged
  • Bacterial Proteins / immunology*
  • Biomarkers
  • Case-Control Studies
  • Female
  • Humans
  • Immunity, Cellular / immunology
  • Immunoglobulin G / metabolism
  • Interferon-gamma / immunology
  • Interferon-gamma / metabolism*
  • Male
  • Membrane Proteins / immunology*
  • Middle Aged
  • Mycobacterium bovis / immunology
  • Mycobacterium tuberculosis / immunology*
  • Mycobacterium tuberculosis / metabolism
  • Prospective Studies
  • T-Lymphocytes / immunology*
  • T-Lymphocytes / metabolism
  • Tuberculosis / diagnosis*
  • Tuberculosis / immunology*


  • Bacterial Proteins
  • Biomarkers
  • ERP protein, Mycobacterium tuberculosis
  • Immunoglobulin G
  • Membrane Proteins
  • Interferon-gamma