T-cell recognition of Mycobacterium tuberculosis culture filtrate fractions in tuberculosis patients and their household contacts

Abstract

We examined the immune responses of patients with active pulmonary tuberculosis (TB) and their healthy household contacts to short-term culture filtrate (ST-CF) of Mycobacterium tuberculosis or molecular mass fractions derived from it. Our goal was to identify fractions strongly recognized by donors and differences among the donor groups of possible relevance for vaccine development. The study population consisted of 65 human immunodeficiency virus-negative donors from the Hossana Regional Hospital, Hossana, Ethiopia. Peripheral blood leukocytes from the donors were stimulated with different antigens and immune responses were determined. Household contacts produced significantly higher levels of gamma interferon (IFN-gamma) than the TB patients in response to antigens present in ST-CF and the 10 narrow-molecular-mass fractions. A similar difference in leukocyte proliferative responses to the antigens between the two groups was also found. In general, while all fractions stimulated immune responses, the highest activity was seen with the low-molecular-mass fractions, which include well-defined TB antigens such as ESAT-6. Leukocytes from contacts of TB patients with severe disease produced higher levels of antigen-specific IFN-gamma than those from contacts of patients with minimal disease. Both groups of contacts exhibited higher cell-mediated responses than the patients themselves. The enhanced immune response of healthy contacts, especially those of patients with severe disease, to secreted mycobacterial antigens is suggestive of an early stage of infection by M. tuberculosis, which could in time result in overt disease or containment of the infection. This possibility is currently being investigated by follow-up studies of the household contacts.

FIG. 1

Individual proliferative responses (A) and IFN-γ levels (B) stimulated by ST-CF or PPD in PBL of TB patients (n = 30) and healthy contacts (n = 35). Median values (solid bars) are indicated.

FIG. 2

Individual proliferative responses (A) and IFN-γ levels (B) stimulated by ST-CF or PPD in PBL of TB patients and healthy contacts segregated on the basis of disease. Patients with minimal TB, n = 8; patients with severe TB, n = 22; contacts of patients with minimal TB, n = 9; contacts of patients with severe TB, n = 26. Median values (solid bars) are indicated.

FIG. 3

Median IFN-γ levels in response to stimulation with 10 molecular mass fractions derived from ST-CF in PBL of TB patients (open bars; n = 30) or healthy contacts (solid bars; n = 35). The migration of molecular mass markers has been indicated at the bottom of the figure.

FIG. 4

Median IFN-γ levels in response to stimulation with 10 molecular mass fractions derived from ST-CF in PBL of healthy contacts, divided on the basis of patients' severity of disease. Patients with minimal TB, n = 8; patients with severe TB, n = 22; contacts of patients with minimal TB, n = 9; contacts of patients with severe TB, n = 26. The migration of molecular mass markers has been indicated at the bottom of the figure.