Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2003
Publication Date: 7/1/2003
Citation: Lee, J., Paape, M., Elsasser, T.H., Zhao, X. 2003. Elevated milk soluble CD 14 in bovine mammary glands challenged with E. Coli lipopolysaccharide. Journal of Dairy Science. 86(7):2382-2389. Interpretive Summary: Recognition of LPS by the innate immune system is critical to elicit inflammatory responses. The cellular receptor for interacting with LPS is CD14, a 53-55 kDa glycosylphosphotidylinositl (GPI)-anchored protein expressed on the membrane of monocytes/macrophages and neutrophils. Although expression of CD14 on neutrophils is weak it can be up-regulated by stimulation with cytokines. In addition, a soluble form of CD14 (sCD14) was found in normal human serum, urine, and milk. Shedding of mCD14 from monocytes and neutrophils has been indicated to be the major source of sCD14 in body fluid . The direct binding of LPS to CD14 is considerably low, however, the presence of LPS-binding protein (LBP), an acute phase protein in the serum, accelerates this process dramatically. In response to LPS/LBP complexes, monocytes/macrophages release a spectrum of cytokines, including TNF-a, IL-1, IL-6, and IL-8, to initial host defense. However, overwhelming production of TNF-a is the main causation of multiple organ failure and death as seen in "septic shock" syndromes. The significance of the findings is that the physiology of mammary gland of the cow may be able to be manipulated to defend against disease by altering the amount of naturally occurring CD14.
Technical Abstract: The purpose of this study was to determine whether soluble CD 14 in milk were affected by the stage of lactation, the level of milk somatic cell count (SCC), the presence of bacteria or lipopolysaccharide (LPS)-induced inflammation. First, milk samples from 100 lactating cows (396 functional quarters) were assayed for sCD14 in milk and their correlation with the stage of lactation, SCC levels and the presence of bacteria infection. Soluble CD14 is higher in transitional milk (0-4 days postpartum) and in milk with higher SCC (> 750,000 cells/ml). No differences were found between non-infected and infected quarters. Second, the left front quarter of 6 healthy lactating cows was challenged with 100 mg LPS in order to study the kinetics of sCD14 during a lipopolysaccharide (LPS)-induced inflammation. Milk samples were collected at various time points until 72 h after infusion. Rectal temperature, milk tumor necrosis factor (TNF)-a, and interleukin-8 (IL-8) increased immediately after the challenge. The increase of sCD14, paralleled to that of SCC, peaked at 12 h and started to decline after 24 h. Serum leakage, as characterized by the level of bovine serum albumin (BSA) in milk, reached its peak at 4 h and gradually dropped afterwards. All the parameters remained at their basal levels in the control quarters during this study. Furthermore, in vitro experiments indicated that neutrophils released sCD14 in response to LPS, in a dose-dependent manner. The results indicate that the concentration of sCD14 is significantly increased in milk after LPS challenge, not likely due to serum leakage. Instead, infiltrated neutrophils might be the main source of sCD14 in milk.