T-cell and serological responses to Erp, an exported Mycobacterium tuberculosis protein, in tuberculosis patients and healthy individuals
1 Laboratoire d'Immunologie Cellulaire, INSERM U543, Hôpital Pitié-Salpêtrière, 47-83, Boulevard de l'Hôpital, 75651 Paris Cedex 13, France
2 Unité de Génétique des Mycobactéries, Institut Pasteur, 25, rue du Docteur ROUX, 75015 Paris, France
3 Service de Médecine Interne, Hôpital Lariboisière, 2, Rue Ambroise Paré, 75010 Paris, France
4 Laboratoire de Bactériologie, Hôpital Pitié-Salpêtrière, 47-83, Boulevard de l'Hôpital, 75651 Paris Cedex 13, France
5 Service des Maladies Infectieuses et Tropicales, Hôpital Pitié-Salpêtrière, 47-83, Boulevard de l'Hôpital, 75651 Paris Cedex 13, France
6 Department of Infectious Diseases and Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, Leiden, Netherlands
BMC Infectious Diseases 2007, 7:83 doi:10.1186/1471-2334-7-83Published: 26 July 2007
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.
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-γ, cytokine production assays and detection of specific human antibodies against recombinant M. tuberculosis proteins.
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-γ 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.
The frequencies of IFN-γ-producing specific T cells, the IFN-γ 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.