Comparison of Natural Resistance-Associated Macrophage Protein (NRAMP)1 Expression between Cows with High and Low Milk Somatic Cells Counts

Abstract

Studies using natural resistance-associated macrophage protein (NRAMP) identification indicated that cattle could be selected for immunity. Several studies performed on intracellular organisms such as Mycobacterium, Salmonella, Brucella and Leishmania in human and mouse revealed that resistance against these bacteria was dependent on high activity of NRAMP in macrophages. However, hardly any researches have been done on Staphylococcus aureus in bovine mastitis, which is an intracellular organism and the main cause of bovine mastitis. The objectives of this study were to establish reverse transcriptase polymerase chain reaction (RT-PCR) methods, through which NRAMP mRNA expression could be compared and analyzed between mastitis-resistant and -susceptible cows. NRAMP gene and its expression were investigated using 20 cows (Holstein Friesian) in Korea. Cows were evenly split into two groups, with and without histories of clinical mastitis. Equivalent numbers of cows were randomly selected from each group. Monocytes were isolated from the bovine peripheral blood of each selected cows and activated with lipopolysaccharide (LPS). mRNA was separated from the monocytes and cDNA of NRAMP was synthesized and amplified using RT-PCR with amplification of β-actin as a control. The difference in NRAMP expressions of mastitis-resistant (n=10) and -susceptible (n=10) Holstein cows was analyzed. Results demonstrate that resistant cows produced more NRAMP mRNA than the susceptible ones, and ratios of NRAMP1:β-actin expression were higher in resistant cows with or without LPS activation. Therefore, this study could be applied to select bovine mastitis resistant cows before infection based on the expression of NRAMP1.