Predominant subpopulations of T lymphocytes in the mammary gland secretions during lactation and intraepithelial T lymphocytes in the intestine of dairy cows

Lymphocytes obtained from mammary gland secretions (MGS) during lactation or the dry period of dairy cows were simultaneously analyzed and compared to ileal intraepithelial lymphocytes (IEL) and peripheral blood lymphocytes (PBL) using monoclonal antibodies (mAb) specific for bovine leukocyte differentiation antigens. The T-lymphocytes of MGS during lactation and those in IEL were predominantly CD8+, while T-cells in MGS during the dry period were predominantly CD4+. In addition, the proportion of γ δ T-cells in MGS during lactation and IEL was fairly high. A large percentage of CD8+ cells and T-cells coexpressed the activation molecule, ACT2, yielding a high proportion of ACT2+ CD8 T-cells and ACT2+ γ δ T-cells, in MGS during lactation and IEL. However, both types of cells were found at an extremely low level in MGS during the dry period and in PBL. Thus, the predominant T-cell populations in MGS during lactation are phenotypically similar to those in IEL in the intestine.