Dissociation between tuberculin skin test and in vitro IFN-gamma responses following neonatal BCG vaccination.

The in vitro IFN-gamma response to tuberculin was recently proposed as a correlate of vaccine-induced immunity to tuberculosis. IFN-gamma also plays a central role in the tuberculin skin test (TST), commonly used as a marker of mycobacterial infection. However, the use of TST as a marker of immunity to tuberculosis is limited for reasons ascribed mainly to interference by environmental mycobacteria. We prospectively investigated the relationship between the TST and cytokine responses to BCG in early infancy, a cohort with relatively low exposure to environmental mycobacteria. Neonatal BCG vaccination induced positive TST responses and predominant IFN-gamma responses to tuberculin in most newborns. However, the production of IFN-gamma, IL-5 and IL-13 was similar in TST responders and non-responders, and there was no significant correlation between the size of TST response and cytokine production. These results indicate that the IFN-gamma assay provides different information than TST in BCG-vaccinated newborns and could be a better marker of vaccine-induced immunity.