Epigenetic states of genes controlling immune responsiveness in bovine chronic mastitis

Mastitis is a common disease in dairy cows, causing substantial economic losses. The leading cause of elevated milk somatic cell count (SC), which is the best indicator for detecting mastitis, is the invasion of pathogens. A major pathogen responsible for bovine mastitis is Staphylococcus aureus, a member of the coagulase-positive staphylococci. Some strains of coagulase-negative staphylococci can also be a cause of clinical or subclinical mastitis. Our study used bisulfite sequencing PCR (BSP) to detect the methylation status of nine candidate genes (CCL2, HCK, F11R, CD8A, PDIA3, LGMN, HSPA1A, IL18 and NFKBIA). We investigated the mechanisms associated with overexpression of these genes, in the mammary gland secretory tissue of cows diagnosed with mastitis and infected with coagulase-positive or coagulase-negative staphylococci. The results showed no changes at the DNA methylation level between the mastitis (CoPS and CoNS) and control groups (H), except for in the HCK region, where the observed differences between the CoPS and H groups were statistically significant. The low methylation level of the CpG sequence seems not to correspond to the previously observed increased activity of these genes, suggesting that mechanisms other than DNA methylation may control mRNA expression at the analyzed loci.