Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/25/2009
Publication Date: N/A
Technical Abstract: An impediment to the development of efficacious vaccines for bovine tuberculosis has been the failure to demonstrate strong associations between immune function and protective immunity. Cytokine gene expression in response to Mycobacterium bovis (M. bovis) infection was evaluated to identify correlates of immunity. Peripheral blood mononuclear cells (PBMC) were isolated and stimulated with either purified protein derivative of M. bovis (PPD), a recombinant fusion protein comprised of 6 kDa early secretory antigenic target and 10 kDa culture filtrate antigen (rESAT6:CFP10), or PBS. After a 16 h incubation period, total leukocyte RNA was isolated and gene expression evaluated using reverse-transcriptase real-time PCR. In addition, gene expression adjacent to gross lesion in the retropharyngeal lymph node (LN) was analyzed. Pathology was evaluated at necropsy. Expression of IFN-gamma, TNF-alpha, iNOS and IL 4 by PBMC increased in response to infection, whereas, IL 10 expression decreased. Differences in gene expression between PBMC from infected and uninfected animals was greatest at 30 dpi. Infected animals were divided into two groups based on pathology. Cells from animals in the high pathology group expressed more IFN-gamma, TNF-alpha, iNOS, IL 4 and IL-5 than did animals in the low pathology group at early time points. Expression of these cytokines correlated with pathology 30 dpi. IL 10 gene expression decreased with time in PBMC from animals in the high pathology group. At 85 dpi, animals in the high pathology group expressed 2-fold less IL 10 mRNA than did animals in the low pathology group and the uninfected controls. At this time point, IL 10 gene expression inversely correlated with pathology. IFN-gamma and iNOS gene expression were significantly greater in tissues from infected animals compared to tissues from uninfected animals. The pathological outcome of M. bovis infection of cattle may be established early after infection since expression of both the TH1 and TH2 cytokines correlated with pathology 30 dpi but not at later time points. In addition, more robust immunological responses were associated with increased pathology. These results suggest that early immune responses play a critical role in establishing the pathological outcome.