Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 17, 2003
Publication Date: July 1, 2003
Citation: Lee, J-W., Paape, M.J., Elsasser, T.H., Zhao, Xin. 2003. Recombinant soluble CD14 reduces severity of intramammary infection by escherichia coli. Infection and Immunity. 71:4034-4039.
Interpretive Summary: Coliform bacteria are the most deadly organisms that dairy cows have to confront on a daily basis. These Gram-negative rod shaped bacteria are found throughout the barns where cows live. When cows lie down on contaminated bedding these bacteria gain easy access into the udders of cows. Once inside the warm, nutritious environment of the mammary gland, they quickly multiply and establish an infection before signals can be sent out for recruitment of specialized white blood cells called neutrophils. By the time the neutrophils arrive the invading bacteria have multiplied into the billions, making their elimination by the neutrophils all but impossible. Toxins secreted by the bacteria act as a poison and destroy the neutrophils and the delicate cells that line the inside of the gland. Massive swelling of the gland occurs, toxins leak out into the blood stream and cause fever, depression and sometimes death of the cow. Now scientists at the USDA at Beltsville, Maryland have discovered a unique way of taking advantage of the poisonous toxin secreted by these coliform organisms. They have produced a protein called CD14. When the scientists injected CD14 into the mammary gland at the time of bacterial challenge, the CD14 binds to the toxin produced by the bacteria. This complex then binds to cells and causes them to secrete chemicals that rapidly attract neutrophils to the infection site. Once there, the bacteria are quickly destroyed and the infection is eliminated. The scientists will use CD14 to prevent mastitis caused by coliform bacteria.
Using a bovine intramammary Escherichia coli infection model, the effect of recombinant bovine soluble CD14 (rbosCD14) on milk somatic cell count (SCC), bacterial clearance and cytokine production was investigated. We first determined whether rbosCD14 would increase SCC during a lipopolysaccharide (LPS) challenge. Three quarters of each of 6 healthy lactating cows were injected with either 0.3 ug LPS, 0.3 ug LPS plus 100 ug rbosCD14 or saline. In comparison with quarters injected with LPS alone, the SCC was two fold higher (P < 0.05) in quarters injected with LPS plus rbosCD14 after challenge. We therefore hypothesized that when E. coli invade the mammary gland, sCD14 in milk would interact with LPS and rapidly recruit neutrophils from blood to eliminate bacteria before establishment of infection. To test this hypothesis, two quarters of each of 9 healthy cows were challenged with either 50 CFU E. coli plus saline or 50 CFU E. coli plus 100 ug rbosCD14. Quarters challenged with E. coli plus rbosCD14 had a more rapid recruitment of neutrophils, which was accompanied by a faster clearance of bacteria, reduced concentrations of TNF-a, IL-8 in milk and reduced clinical symptoms than challenged quarters injected with saline. Results indicate that increasing the concentration of sCD14 in milk might be a potential strategy to prevent or reduce severity of infection by coliform bacteria.