Exposure to Mycobacterium avium decreases the protective effect of the DNA vaccine pVAXhsp65 against Mycobacterium tuberculosis-induced inflammation of the pulmonary parenchyma

This work investigated the effect of previous Mycobacterium avium exposure on the protective ability of the DNA vaccine pVAXhsp65 against inflammation in the pulmonary parenchyma. BALB/c mice were presensitized with heat-killed M. avium and then immunized with three doses of pVAXhsp65 prior to challenge with Mycobacterium tuberculosis. M. avium sensitization induced high levels of spontaneous IL-5 production that were concomitant with a positive delayed-type hypersensitivity reaction; antigen-specific IFN-γ production was also observed upon splenocyte stimulation. Prior exposure to M. avium resulted in altered cytokine and antibody production induced by immunization with pVAXhsp65; instead of a Th1 response, vaccinated mice previously exposed to M. avium developed a strong Th2 response. This switch to a Th2 response coincided with the loss of the anti-inflammatory effect of pVAXhsp65 vaccination previously observed in the pulmonary parenchyma of mice infected with M. tuberculosis. These results suggest that exposure to environmental mycobacteria can modulate immune responses induced by mycobacterial vaccines other than bacillus Calmette-Guérin.

Neonatal BCG immunization followed by DNAhsp65 boosters: highly immunogenic but not protective against tuberculosis - a paradoxical effect of the vector?

A new tuberculosis vaccine is urgently needed. Prime-boost strategies are considered very promising and the inclusion of BCG is highly desirable. In this investigation, we tested the protective efficacy of BCG delivered in the neonatal period followed by boosters in the adult phase with a DNA vaccine containing the hsp65 gene from Mycobacterium leprae (pVAXhsp65). Immune responses were characterized by serum anti-hsp65 antibody levels and IFN-gamma and IL-5 production by the spleen. Amounts of these cytokines were also determined in lung homogenates. Protective efficacy was established by the number of colony-forming units (CFU) and histopathological analysis of the lungs after challenge with Mycobacterium tuberculosis. Immunization with BCG alone triggered a significant reduction of CFU in the lungs and also clearly preserved the pulmonary parenchyma. BCG priming also increased the immunogenicity of pVAXhsp65. However, boosters with pVAXhsp65 or the empty vector abolished the protective efficacy of BCG. Also, higher IL-5 levels were produced by spleen and lungs after DNA boosters. These results demonstrated that neonatal BCG immunization followed by DNAhsp65 boosters is highly immunogenic but is not protective against tuberculosis.

Immunomodulatory activities associated with β-glucan derived from Saccharomyces cerevisiae

In this study we investigated the effect of beta-glucan derived from Saccharomyces cerevisiae on fungicidal activity, cytokine production and natural killer activity. Spleen and peritoneal cells from female C57BL/6 mice, previously injected (24 or 48 h) with 20 or 100 microg of glucan by i.p. route, were assayed. In vivo beta-glucan administration primed spleen cells for a higher production of IL-12 and TNF-alpha when S. aureus was used as a stimulus. In addition, beta-glucan increased NK spleen cells activity against YAC target cells. Some immunomodulatory activities not yet described for beta-glucan were observed in this work.

Immunomodulatory activities associated with beta-glucan derived from Saccharomyces cerevisiae

In this study we investigated the effect of beta-glucan derived from Saccharomyces cerevisiae on fungicidal activity, cytokine production and natural killer activity. Spleen and peritoneal cells from female C57BL/6 mice, previously injected (24 or 48 h) with 20 or 100 microg of glucan by i.p. route, were assayed. In vivo beta-glucan administration primed spleen cells for a higher production of IL-12 and TNF-alpha when S. aureus was used as a stimulus. In addition, beta-glucan increased NK spleen cells activity against YAC target cells. Some immunomodulatory activities not yet described for beta-glucan were observed in this work.

Down-modulation of lymphoproliferation and interferon-gamma production by beta-glucan derived from Saccharomyces cerevisiae

beta-glucan, one of the major cell wall components of Saccharomyces cerevisiae, has been found to enhance immune functions. This study investigated in vivo and in vitro effects of beta-glucan on lymphoproliferation and interferon-gamma (IFN-gamma) production by splenic cells from C57BL/6 female mice. All experiments were performed with particulate beta-glucan derived from S. cerevisiae. Data demonstrated that both, i.p. administration of particulate beta-glucan (20 or 100 micrograms/animal) and in vitro stimulation of splenic cells (20 or 100 micrograms/ml of culture) decreased lymphoproliferation and IFN-gamma production induced by concanavalin A. These results suggest that beta-glucan can trigger a down-modulatory effect regulating a deleterious immune system hyperactivity in the presence of a strong stimulus.