In this study we investigated the ability of different Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) strains to survive in bovine monocyte-derived macrophages (MDMs) of cows naturally infected with M. paratuberculosis and control cows. We tested the hypotheses that infection status of cows affects macrophage killing ability and that survival of M. paratuberculosis in macrophages is dependent on the strain. Peripheral blood mononuclear cells (PBMC) were obtained from Johne's disease-positive (n = 3) and age and stage of lactation matched Johne's disease-negative (n = 3) multiparious cows. Following differentiation, MDMs were challenged in vitro with four M. paratuberculosis strains of different host specificity (cattle and sheep). Two hours and 2, 4, and 7 days after infection, ingestion, and intracellular survival of M. paratuberculosis strains were determined by fluorescence microscopy. There was no effect of the origin of MDMs (Johne's disease-positive or control animals) on phagocytosis, survival of bacteria, or macrophage survival. In contrast, important strain differences were observed. These findings suggest that some M. paratuberculosis strains interfere more successfully than others with the ability of macrophages to kill intracellular pathogens which may make it important to include strain typing when designing control programs.
Bibliographical noteFunding Information:
We acknowledge the excellent technical support of Suzanne Klaessig. We also wish to thank Kenneth W. Simpson, Nancy A. Lorr, and Wilhelm H. Elmore for provision of laboratory facilities and technical support. Further we would like to thank Judy McAlister for helpful discussions and critical reading of the manuscript. We also gratefully acknowledge the owner of the animals included in this study for his collaboration. Financial support for this work was provided in part by the USDA Agricultural Research Service (Agreement No. 58-1265-3-156) for the Regional Dairy Quality Management Alliance. Funding was also provided by the Johne's Disease Integrated Program (USDA contract 45105). Johne's disease research in SS laboratory is supported by JDIP and USDA-NRI grants.
Copyright 2008 Elsevier B.V., All rights reserved.
- Genetic susceptibility
- Mycobacterium paratuberculosis