Effects of parturition and dexamethasone on DNA methylation patterns of IFN-γ and IL-4 promoters in CD4+ T-lymphocytes of Holstein dairy cows.

This study investigated epigenetic mechanisms by which DNA methylation affects the function of bovine adaptive immune system cells, particularly during the peripartum period, when shifts in type 1 and type 2 immune response (IR) biases are thought to occur. Stimulation of CD4+ T-lymphocytes isolated from 5 Holstein dairy cows before and after parturition with concanavalin A (ConA) and stimulation of CD4+ T-lymphocytes isolated from 3 Holstein dairy cows in mid-lactation with ConA alone or ConA plus dexamethasone (Dex) had significant effects on production of the cytokines interferon gamma (IFN-gamma, type 1) and interleukin 4 (IL-4, type 2) that were consistent with DNA methylation profiles of the IFN-gamma gene promoter region but not consistent for the IL-4 promoter region. ConA stimulation increased the production of both cytokines before and after parturition. It decreased DNA methylation in the IFN-gamma promoter region but increased for IL-4 promoter region. Parturition was associated with an increase in IFN-gamma production in ConA-stimulated cells that approached significance. Overall, DNA methylation in both promoter regions increased between the prepartum and postpartum periods, although this did not correlate with secreted cytokine concentrations. Dexamethasone treated cells acted in a manner consistent with the glucocorticoid's immunosuppressive activity, which mimicked the change at the IFN-gamma promoter region observed during parturition. These results support pregnancy as type 2 IR biased, with increases of IFN-gamma occurring after parturition and an increase in IL-4 production before calving. It is likely that these changes may be epigenetically controlled.