Sensitization with johnin purified protein derivative augments interferon-gamma production in cows infected with Mycobacterium avium subsp. paratuberculosis

摘要

Measurement of secreted IFN-gamma has proven to be a valuable tool for the detection of animals infected with mycobacterial pathogens,including Mycobacterium avium subsp. paratuberculosis. Previous reports have suggested that tuberculin skin testing can influence the performance of the IFN-gamma assay. In the present study, healthy noninfected cows, and cows subclinically and clinically infected with MAP were administered an intradermal injection of johnin purified protein derivative and effects on secreted and intracellular IFN-gamma were observed. Significant increases in secreted IFN-gamma were noted in antigen-stimulated PBMC isolated from subclinically infected cows within 2 days of the skin test. Results for intracellular IFN-gamma were more variable than those noted for secreted IFN-gamma. Stimulation of peripheral blood mononuclear cells with medium only (nonstimulated), pokeweed mitogen, and JPPD resulted in transient elevations in intracellular IFN-gamma, depending upon infection status of the animals and in vitro stimulant. When averaged over each bleeding day of the study, intracellular IFN-gamma was higher within CD4+ and CD8+ subpopulations for infected cows compared to healthy controls throughout the study. When T cell populations were further defined by CD45RO expression, intracellular IFN-gamma was higher for CD8+/CD45RO+ lymphocytes compared to CD4+/CD45RO+ cells. These results indicate that intradermal sensitization of cows in the early stage of infection with antigen will enhance the sensitivity of detection by the IFN-gamma assay. In addition, CD8+ lymphocytes appear to play an important role as a mediator of MAP infection in naturally exposed cattle.