Abstract
A role for gamma 8 T cells in protection against mycobacterial infections including Johne's disease (JD) has been suggested. In neonatal calves where the risk to infection with Mycobacterium avium subsp. paratuberculosis (MAP) is high, the majority of circulating CD3(+) lymphocytes are gamma delta TCR+. Bovine y8 T cells are divided into two major subsets based on the surface expression of workshop cluster 1 (WC1). The WC1(+) subset, the predominant subset in periphery, is further divided into WC1.1(+) and WC1.2(+) subpopulations. The ability of gamma delta T cells to produce IFN-gamma prior to CD4(+) alpha beta T cell activation could be crucial to the outcome of MAP infection. In the current study, cattle were naturally infected with MAP and were classified as either in the subclinical or clinical stage of infection. Compared to the control non-infected group, gamma delta T cell frequency in circulating lymphocytes was significantly lower in the clinical group. The observed decline in frequency was restricted to the WC1.2(+) subset, and was not associated with preferential migration to infection sites (distal-ileum). gamma delta T cells proliferated significantly in recall responses to stimulation with purified protein derivative from MAP (PPD-J) only in sub clinically infected cattle. These responses were a heterogeneous mixture of WC1.1 and WC1.2 subsets. Proliferation and IFN-gamma production by the WC1.1(+) gamma delta T cell subset was significantly higher in the subclinical group compared to the control and clinical groups. Our data indicates differences in MAP-specific ex-vivo responses of peripheral WC1(+) gamma delta T cells of cattle with the subclinical or clinical form of JD.