Peripheral blood and milk leukocytes subsets of lactating Sarda ewes

Leukocytes subpopulations in blood and milk of lactating Sarda ewes were investigated. Animals characterized by a SSC level <500×10 3 cells/mL and a negative bacteriological examination were sampled in early, mid and late lactation. Milk differential cell count evidenced that macrophage represented the main population (42.8%±3.5) followed by lymphocytes (40.2%±3.4) and neutrophils (8,6%±2.1). Flow cytometry analysis showed that lymphocytes subsets in milk were quite different from blood. High CD8 + and low CD4 + lymphocytes percentages determined a CD4/CD8 ratio inversion in milk compared to blood (0.3%±0.03 vs 1.8%±0.08). CD8 + decreased while, conversely, CD4 + increased in late lactation. γδ T cells were more represented in milk (12.6%±1.3) than in blood (6.8%±0.3) and their proportions appeared similar throughout lactation in both compartments. IL-2 receptor was mainly expressed in milk on T cytotoxic lymphocytes. Data obtained in uninfected mammary glands could allow an early discrimination between physiological and pathological changes occurring in ewe milk. Further phenotypical and functional studies on milk leukocytes subsets might help to understand defense mechanisms of the ovine mammary gland against IMI.