Vaccine-induced cytokine responses in a guinea pig model of pulmonary tuberculosis

Guinea pigs exposed to very small numbers of virulent tubercle bacilli by the respiratory route develop a disease which mimics many of the important features of the pathogenesis of human tuberculosis (TB), including the expression of strong protective immunity following vaccination with BCG. In order to elucidate the precise immunological mechanisms of vaccine-induced resistance in this model, both mRNA and protein assays for several guinea pig cytokines and chemokines have been developed. The coordinated expression of cytokine and chemokine mRNA and protein was examined in various leukocyte populations and in inflammatory cells and fluid collected following the induction of tuberculous pleurisy in BCG-vaccinated guinea pigs. Real-time RT-PCR assays revealed that the mRNA levels for IFNγ, TNFα, and IL-8 rose over the first few days of TB pleuritis and then declined over the 9 days of the study. Injection of anti-TGFβ on day 8 following pleurisy induction resulted in significant changes in cytokine mRNA levels and PPD-induced proliferation in pleural effusion lymphocytes taken 24 h later. BCG vaccination induced significantly higher levels of bioactive TNFα protein in the supernatants of alveolar, peritoneal and splenic cells from BCG-vaccinated guinea pigs cultured in the presence of attenuated or virulent mycobacteria. In sharp contrast, following virulent challenge, all three cell types from BCG-vaccinated guinea pigs produced significantly less TNFα. Thus, BCG vaccination appears to modulate the potentially harmful effects of TNFα in this model of pulmonary TB. Levels of mRNA for IL-12p40 were upregulated by exposure of infected and uninfected macrophages to recombinant guinea pig (rgp)TNFα. The intracellular survival of mycobacteria was enhanced when endogeous TNFα activity was neutralized with anti-rgpTNFα antiserum. rgp RANTES (CCL5) upregulated mRNA levels for TNFα, IL-1β, MCP-1 (CCL2), and IL-8 (CXCL8) in alveolar and peritoneal macrophages. These results illustrate the profound effects of prior vaccination with BCG on the cytokine and chemokine responses of distinct cell populations in the guinea pig following exposure to attenuated and virulent strains of M. tuberculosis.