38 000 MW antigen-specific major histocompatibility complex class I restricted interferon-gamma-secreting CD8(+) T cells in healthy contacts of tuberculosis

CD8(+) T lymphocytes are required to protect mice against Mycobacterium tub erculosis, 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 tub erculosis could be detected in infected humans. Using a recombinant vaccini a virus expressing the 38000 MW antigen of M. tuberculosis (rV38) and a con trol vaccinia virus (rVras) we demonstrated that both viruses stimulated IF N-gamma production from freshly isolated peripheral blood mononuclear cells (PBMC) in a 36-hr enzyme-linked immunospot assay. Cell depletion and antib ody blockade established that the bulk of the 38000 MW antigen-specific IFN -gamma, response was mediated by CD8(+), major histocompatibility complex c lass I-restricted T cells, whereas the anti-vaccinia Virus response was pre dominantly mediated by CD4(+) T cells. In further evaluations PBMC from all seven healthy tuberculosis-exposed contacts had a 38 000 MW antigen-specif ic IFN-gamma response, whereas seven patients with untreated sputum-positiv e pulmonary tuberculosis had very low levels of 38 000 antigen-specific IFN -gamma-producing cells. These preliminary observations demonstrate the util ity of recombinant vaccinia Viruses in restimulating freshly isolated CD4() and CD8(+) T cells. The bias towards a higher frequency of IFN-gamma-prod ucing CD8(+) T cells in contacts rather than patients may indicate a protec tive role for CD8(+) cells in human tuberculosis.