Longitudinal evaluation of CD4+and CD8+peripheral blood and mammary gland lymphocytes in cows experimentally inoculated with Staphylococcus aureus

Staphylococcus aureus is a major pathogen associated with mastitis, a disea se affecting both women and dairy cows. The longitudinal profiles of bovine peripheral blood and mammary gland lymphocyte phenotypes in response to S. aureus-induced mastitis were investigated in dairy cows. Increased percent age of CD4 lymphocytes in the mammary gland between 1 and. 8 days post-inoc ulation, increased milk CD4 protein density per cell between 1-8 days post- inoculation, and a statistically significant negative correlation between p ost-inoculation bacterial counts in milk and blood lymphocyte CD4 protein d ensity were found. Together with blood and milk leukocyte counts, the milk lymphocyte CD4/CD8 ratio and the milk lymphocyte CD4 protein density were m ore informative indicators than milk somatic cell counts and bacteriology f or identification of early vs. late inflammatory phases. These findings sug gest that CD4+ lymphocytes play a protective role in the early stages of S. aureus-induced mastitis.