Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/16/1998
Publication Date: N/A
Citation: Interpretive Summary: Scientists in the Immunology and Disease Resistance Laboratory, USDA-ARS, Beltsville together with scientists in INRA, France, developed a procedure for quantitating the killing power of neutrophils, a type of white blood cell that protects the body from infection. Using this procedure, the scientists discovered that two compounds called tumor necrosis factor and complement accelerated the rate of killing of Staphylococcus aureus by neutrophils 5 to 10 times. Staphylococcus aureus is an organism that is especially difficult to treat once it invades the mammary gland of cows. Tests are underway to determine if treatment of udders infected with these compounds will be effective in eliminating infections caused by Staphylococcus aureus.
Technical Abstract: An assay which measures the rates of phagocytosis and intracellular killing of Staphylococcus aureus was developed. After short periods of incubation, bacteria and phagocytes are separated by differential centrifugation and viable cell-free and cell-associated bacteria are quantified. Preopsonized bacteria were added to neutrophils at a bacterium-to-neutrophil ratio of 2:1. Incubation was carried out under gentle agitation at 37C and samples were taken after 10 and 20 min. Extracellular bacteria were separated by centrifugation. Washed neutrophil pellets were lysed by mild sonic treatment to release intracellular bacteria. Samples were spread on nutrient agar plates and numbers of viable extracellular and intracellular bacteria determined. Priming of neutrophils with TNF-a or C5a stimulated bactericidal activity. The rate of intracellular killing was accelerated 5 to 10 times as compared to unstimulated cells, with killing half-time of about 2 min when the two priming agents were combined.