Setting: Immune response induced by BCG vaccination seems to reflect the development of T-cell immunity and monocyte activation. Participants were recruited from a large prospective study in infants from a suburb in Santiago, Chile.
Objective: To determine whether newborn BCG immunization changes the innate ability of cultured monocyte-macrophages to ingest and kill virulent mycobacteria in the absence of lymphocytes.
Design: The study population consisted of 15 three-month-old, tuberculin-positive infants immunized with BCG (Japanese) at birth, 13 randomly-selected, age-matched tuberculin-nonreactive infants in whom BCG immunization was postponed until one year of age, and five BCG-immunized, tuberculin-reactive adults. Adherent cells were cultured for 48 h. Monocyte-macrophage viability and number and viability of intracellular Mycobacterium tuberculosis bacilli were assessed after an additional 2 h and 4 and 7 days of incubation.
Results: There was no difference in the mean number of adherent cells present after 48 h among the three study groups. Adherent cells from BCG-immunized infants and adults had a significantly higher viability after 7 days in culture than adherent cells from non-immunized infants. The percentage of cells ingesting M. tuberculosis and the number of bacilli per cell after 2 h and 4 days was significantly higher in immunized infants and adults than in non-immunized infants. However, there was no evidence for increased killing of mycobacteria by cells from immunized infants and adults.
Conclusion: These results suggest that BCG vaccination increases monocyte viability and the uptake of M. tuberculosis without enhancing the ability to kill ingested M. tuberculosis in the absence of lymphocytes.