Study of T-lymphocyte subsets of healthy and Mycobacterium avium subsp. paratuberculosis-infected cattle

The relative contributions of T-lymphocyte subsets to host defense in cattle infected with Mycobacterium avium subsp. paratuberculosis is reported. The subsets were purified with appropriate monoclonal antibodies and a magnetic bead column separation system, and their purity was verified by flow cytometry. Biological activity of each subset, expressed as lymphoproliferation and gamma interferon (IFN-gamma) production, was measured in response to phytohemagglutinin (PHA) and an M. avium antigen preparation (A-PPD). IFN-gamma was measured by antibody capture enzyme-linked immunosorbent assay. The results showed a correlation between proliferation and IFN-gamma production in response to A-PPD but not to PHA. In response to PHA, CD4(+) lymphocytes were the most prolific producers of IFN-gamma. CD8(+) lymphocytes produced IFN-gamma to a lesser extent, whereas gamma delta(+) T lymphocytes produced little or no IFN-gamma. Differences observed between the amount of IFN-gamma produced by CD4(+) versus CD8(+) cells and CD4(+) versus gamma delta(+) cells were significant (P < 0.01), but those between peripheral blood mononuclear cells (PBMC) and CD4(+) T cells were not. Similar responses to A-PPD were observed except that PBMC produced higher levels of IFN-gamma than did CD4(+) T cells. These data for cattle are similar to observations made for other animal species, where CD4(+) cells are the major type of T lymphocytes producing IFN-gamma. They further suggest that whatever the role gamma delta(+) T cells may play in paratuberculosis, it is not likely to be mediated by IFN-gamma production.