Bovine Milk Lymphocytes Display the Phenotype of Memory T Cells and Are Predominantly CD8

Abstract The phenotype of bovine milk lymphocytes was investigated and compared to peripheral blood lymphocytes using monoclonal antibodies specific for bovine leukocyte differentiation antigens and flow cytometry. T Lymphocytes traffic selectively into bovine milk while B lymphocytes represent a minor population in milk by comparison to peripheral blood. The vast majority of T cells in milk express αβ T cell receptors and are predominantly CD8 + . T cells in milk express twofold higher levels of CD2 and fivefold lower levels of CD45R, characteristics associated with memory T cells. Grouping of cows by lactational stage and analysis of lymphocyte subpopulation percentages indicated that CD4 + T cells are present in relatively low numbers in milk of cows in the first 50 days of lactation and have a significant tendency to increase in number as lactation progresses.