The immune response to vaccination with Bacillus Calmette-Guerin (BCG), the only tuberculosis vaccine available, has not been fully characterized. We used multiparameter flow cytometry to examine specific T cell cytokine production and phenotypic profiles in blood from 10-week old infants, routinely vaccinated with BCG at birth. Ex vivo stimulation of whole blood with BCG for 12 hours induced expression of predominantly IFN-γ, IL-2 and TNF-α in CD4+ T cells, in 7 distinct cytokine combinations. IL-4 and IL-10 expression were detected in CD4+ T cells at low frequencies, and only in cells that did not co-express Type 1 cytokines. Specific CD8+ T cells were less frequent than CD4+ T cells, and produced mainly IFN-γ and/or IL-2, and less TNF-α, IL-4 and IL-10. Importantly, many mycobacteria-specific CD4+ and CD8+ T cells did not produce IFN-γ. The predominant phenotype of BCG-specific Type 1 T cells was that of effector cells, i.e., CD45RA–CCR7–CD27+, which may reflect persistence of M. bovis BCG in infants until 10 weeks of age. Among 5 phenotypic patterns of CD4+ T cells, central memory cells were more likely to be IL-2+, and effector cells more likely to be IFN-γ+. We concluded that neonatal vaccination with BCG induces T cells with a complex pattern of cytokine expression and phenotypes. Measuring IFN-γ production alone underestimates the magnitude and complexity of the host cytokine response to BCG vaccination, and may not be an optimal readout in studies of BCG and novel tuberculosis vaccination.

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Vaccination with Mycobacterium bovis bacille Calmette-Guerin (BCG) has variable efficacy in preventing tuberculosis. Both BCG strain and route of administration have been implicated in determining efficacy; however, these variables are not considered in current clinical recommendations for vaccine choice. We evaluated antigen-specific immunity after percutaneous or intradermal administration of Japanese BCG or intradermal administration of Danish BCG. Ten weeks after vaccination of neonates, percutaneous Japanese BCG had induced significantly higher frequencies of BCG-specific interferon- gamma -producing CD4(+) and CD8(+) T cells in BCG-stimulated whole blood than did intradermal Danish BCG. Similarly, percutaneous vaccination with Japanese BCG resulted in significantly greater secretion of the T helper 1-type cytokines interferon- gamma, tumor necrosis factor- alpha , and interleukin-2; significantly lower secretion of the T helper 2-type cytokine interleukin-4; and greater CD4(+) and CD8(+) T cell proliferation. Thus, BCG strain and route of neonatal vaccination confer different levels of immune activation, which may affect the efficacy of the vaccine.

Salmonella enterica serovar Typhimurium invasion genes are necessary for bacterial invasion of intestinal epithelial cells and are thought to allow salmonellae to enter and cross the intestinal epithelium during infection. Many invasion genes are encoded on Salmonella pathogenicity island 1 (SPI1), and their expression is activated by HilA, a transcription factor also encoded on SPI1. We have studied the role of Salmonella invasion genes during infection of mice following intragastric inoculation. We have found that strains containing a mutation in hilA or invG were recovered from the intestinal contents, intestinal tissues, and systemic tissues at a lower frequency than their parental wild-type strain. In contrast, a strain in which SPI1 is deleted was recovered from infected mice at a frequency similar to that of its parental wild-type strain. The ⌬SPI1 phenotype indicates that S. enterica does not require invasion genes to cross the intestinal epithelium and infect systemic tissues. This result has forced us to reconsider the long-held belief that invasion genes directly mediate bacterial infection of the intestinal mucosa and traversion of the intestinal barrier during infection. Instead, our results suggest that hilA is required for bacterial colonization of the host intestine. The seemingly contradictory phenotype of the ⌬SPI1 mutant suggests that deletion of another gene(s) encoded on SPI1 suppresses the hilA mutant defect. We propose a model for S. enterica pathogenesis in which hilA and invasion genes are required for salmonellae to overcome a host clearance response elicited by another SPI1 gene product(s).