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 IFN gamma, TNF alpha, 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-TGF beta 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 TNF alpha 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 TNF alpha Thus, BCG vaccination appears to modulate the potentially harmful effects of TNF alpha 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)TNF alpha The intracellular survival of mycobacteria was enhanced when endogeous TNF alpha activity was neutralized with anti-rgpTNF alpha antiserum. rgp RANTES (CCL5) upregulated mRNA Levels for TNF alpha IL-1 beta, 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 A tuberculosis. (c) 2005 Elsevier Ltd. All rights reserved.