On the trail of regulatory T cells in blood and tissues of Mycobacterium paratuberculosis infected cattle (170.8)

Abstract

Abstract Based on previous observations, it is proposed that induced regulatory T cells (Tregs) form an important aspect of immune responses to Mycobacterium avium subspecies paratuberculosis (MAP) in cattle. Tregs are typically CD4+CD25+ and express the FoxP3 transcription factor. Removal of CD25+ T cells from peripheral blood mononuclear cells (PBMCs) isolated from MAP infected cattle prior to stimulation with MAP antigens enhances production of IFNγ mRNA and reduces production of IL-10 mRNA from remaining cells. To more definitively identify antigen-specific Tregs in MAP infected cattle, we have begun to analyze cell populations using multi-color flow cytometry and intracellular staining. Tregs in tissues have been visualized using multi-color confocal microscopy and immunohistochemical staining. As expected, stimulation of PBMCs from infected cattle with MAP enhances the percent CD3+ cells that are also CD25+ (25%, +/-2.8%), relative to nil stimulated cells (6.4%, +/- 3.8%). Expression of the FoxP3 transcription factor is more variable with some animals showing up regulation following stimulation with MAP (20%-50% of CD25+ cells) relative to nil stimulation (~6%). Thus, in some cattle, CD25+FoxP3+ cells do indeed form a significant proportion of cells responding to MAP antigen stimulation. FoxP3 positive cells are also a significant feature in many lesions associated with MAP infection, although it is not yet known if these cells are antigen specific.