Phenotype analysis of peripheral blood mononuclear cells in periparturient dairy cows.

Impaired immune function during the periparturient period contributes to the increased susceptibility of the cow to infectious disease around the time of calving. Changes in subpopulations of peripheral blood mononuclear cells during the immediate periparturient period can contribute to the observed immunosuppression in cows, but it is not known exactly when and what changes occur. Using a flow cytometer and monoclonal antibodies directed against antigenic markers on mononuclear cells, the populations of CD3, CD4, CD8, and gamma delta T-cell receptor positive cells were examined in eight periparturient Jersey cows during the 2 wk before and 2 wk after parturition. The percentage of cells that were positive for CD3, CD4, and gamma delta T-cell receptor markers exhibited a significant decline before calving and reached a nadir at calving. These percentages did not return to precalving levels until 2 wk after calving. These data are compatible with the hypothesis that declining T-cell populations may contribute to the immunosuppression reported for dairy cows at calving.