Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/1998
Publication Date: N/A
Interpretive Summary: Bacterial infections of the mammary gland cost US dairymen $2 billion annually. Antibiotics are only partially effective and their effectiveness is decreasing with the development of resistant strains. Use of antibiotics necessitates discarding the milk for several days due to the potential danger to the public of antibiotic contaminated milk and development of antibiotic resistant bacteria. To minimize and hopefully eliminate the use of antibiotics, researchers have sought means of enhancing the cow's natural defense mechanisms. This requires an in-depth knowledge of the relationship of mammary gland defense mechanisms to the whole animal. As in any bacterial invasion of the body, the blood supplies the cellular and humoral factors needed to combat the invading organism. The presence of large numbers of white blood cells (neutrophils) in the mammary gland has been shown to protect the cow from bacterial infection. However, milk quality control requires that milk contain cell counts far bellow the protective level. Understanding the mechanism(s) of neutrophil migration from blood into milk will aid in the development of methods to effect rapid movement of neutrophils into the mammary gland in response to invading bacteria. This study identified a substance in the milk (C5a)and surface components of neutrophils (CD11b/CD18) and cells lining the blood vessels and the lumen of the mammary gland (integrins) essential to the transport of neutrophils from blood to milk. These data fill an important gap in our understanding of stimuli effecting neutrophil movement from blood to milk and will aid in the developing means of enhancing cow response to bacterial invasion of the mammary gland.
Technical Abstract: Neutrophil recruitment from the blood stream into the mammary gland is important during bovine mastitis. In vivo neutrophils migrate into the extracellular matrix and then across mammary endothelium in the apical- to-basolateral direction into the infected mammary gland lumen. Therefore, we investigated the mechanisms required for chemoattractant-stimulated neutrophil transmigration through a monolayer of primary mammary endothelium, through a collagen type I matrix and through a monolayer of primary mammary epithelium. Complement factor C5a induced a time-dependent neutrophil migration across all three barriers. The relative rank order of hindrance to neutrophil diapedesis for the three barriers was: epithelium > endothelium > collagen type I matrix. Neutrophil migration across collagen type I was partially inhibited by mAb to CD18, that recognizes the beta chain of the beta-2 integrins, but no inhibition was observed by mAb to CD11b, the alpha chain of the beta-2 integrins. Neutrophil migration across mammary endothelial cells was almost completely CD18-dependent diapedesis across mammary epithelial cells was dependent more on CD11b. These results provide evidence for different CD11b/CD18-dependent mechanisms of C5a-stimulated neutrophil diapedesis across the blood/milk barrier.