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proliferation and cytokine production profiles by blood mononuclear cells in response to in vitro stimulation with mycobacterial antigens were compared in patients with active tuberculosis and in sensitized healthy controls. Interleukin-4 (IL-4) and interferon-7 (IFN-γ) were detected at single-cell level using the ELISPOT assay. Patients showed significantly (P < 0.01) increased numbers of IL-4 secreting cells and decreased thymidine incorporation, but no significant difference in IFN-γproducing cells in response to the 38,000 MW or 19,000 MW antigens and their immunodominant peptide epitopes. Pronounced individual variations were found in both patient and control groups, when comparing the responsiveness to the mycobacterial extract, two protein antigens and five synthetic peptides. None of the antigens or peptides tested showed preferential stimulation of either IL-4- or IFN-γ-secreting T cells, and proliferation was not correlated with either IL-4 or IFN-γ production. In particular, cytokine responsiveness was of similar frequency in subjects who did or did not show positive proliferation, indicating that the latter test was not fully representative of the active T-cell repertoire. It is concluded that the demonstrated Th2 type of profile in response to two prominent mycobacterial antigens may play a role in the mechanisms of defective host resistance in tuberculosis. [ABSTRACT FROM AUTHOR]

CD8+ T lymphocytes are required to protect mice against Mycobacterium tuberculosis, although in early infection the mechanism appears not to be via perforin or granzyme-mediated lysis of the infected target, and may be via interferon-gamma (IFN-gamma) production. We therefore investigated whether CD8+ T cells specific for the immunoprotective 38 000 MW antigen of M. tuberculosis could be detected in infected humans. Using a recombinant vaccinia virus expressing the 38 000 MW antigen of M. tuberculosis (rV38) and a control vaccinia virus (rVras) we demonstrated that both viruses stimulated IFN-gamma production from freshly isolated peripheral blood mononuclear cells (PBMC) in a 36-hr enzyme-linked immunospot assay. Cell depletion and antibody blockade established that the bulk of the 38 000 MW antigen-specific IFN-gamma response was mediated by CD8+, major histocompatibility complex class I-restricted T cells, whereas the anti-vaccinia virus response was predominantly mediated by CD4+ T cells. In further evaluations PBMC from all seven healthy tuberculosis-exposed contacts had a 38 000 MW antigen-specific IFN-gamma response, whereas seven patients with untreated sputum-positive pulmonary tuberculosis had very low levels of 38 000 antigen-specific IFN-gamma-producing cells. These preliminary observations demonstrate the utility of recombinant vaccinia viruses in restimulating freshly isolated CD4+ and CD8+ T cells. The bias towards a higher frequency of IFN-gamma-producing CD8+ T cells in contacts rather than patients may indicate a protective role for CD8+ cells in human tuberculosis.