Relationship between blood lymphocyte phenotype, DRB1 (MHC class II) gene polymorphism and somatic cell count in ewe milk

The aim of the study was to analyse the variability of the leukocyte population and lymphocyte subpopulation in peripheral blood in ewes of different age and mammary gland health status and with different genotype in DBR1 (MHC II) gene. Blood samples were collected 3 times from 24 ewes of Polish Heath Sheep at the age of 6, 12 and 24 months. Milk samples were collected from ewes at the age of 24 months, during their first lactation period. The status of the mammary gland was established according to the number of somatic cell count (SCC) in 1 ml of milk, with 300 000 cells/ml established as a maximum for a healthy gland. Consequently, all the ewes were divided into two groups with cell count <300 000 (healthy = H) and > 300 000 (mastitic = M). A statistically significant increase in number of neutrophils, eosinophils, monocytes, CD2+ and CD4+ lymphocytes and statistically significant decrease in the number of CD19+, WC1-N2+ and CD8+ lymphocytes and MHC II+ cells in older animals (24 months of age) were observed. Additionally, 24 month old ewes of the H group being at the age of 6 months showed higher percentage of CD2+, CD19+ (P <= 0.05), CD8+ (P <= 0.05) lymphocytes as well as MHC II+ cells (P <= 0.01) comparing to the ewes of the same age from M group. Also not significant increase in CD4+ and WC1-N2+ lymphocyte number was found. Analysis of microsatellite polymorphism of DRB1 gene fragment identified the presence of 8 alleles. One of them, of 526 bp length, was of particular interest as it was most frequently found in group H ewes. Moreover, its presence was associated with several times higher percentage of CD2+, CD8+, CD19+ lymphocytes and MHC II+ cells in peripheral blood, when compared to other alleles.