Bactericidal activity of fractionated granule contents from human polymorphonuclear leukocytes: role of bacterial membrane lipid

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Abstract
Granule contents from human polymorphonuclear leukocytes were prepared by extraction with 0.2 M acetate, pH 4. A buffer extract fraction (peak D) obtained by Sephadex G-100 column chromatography demonstrated distinct antimicrobial activity toward Acinetobacte sp. independent of added H2O2 or Cl-. The protein of this fraction had an apparent molecular weight of 9,000 and demonstrated time and dose dependence that was more active against stationary-growth cells than mid-log-phase cells. The bactericidal activity of the fraction was most active at 37 degrees C, with only slight activity demonstrated at 22 degrees C and no activity at 4 degrees C. Boiling the granule fraction for 30 min did not affect the antimicrobial activity. However, pronase or trypsin pretreatment of the peak D fraction reduced its antimicrobial activity. When the membrane lipid composition of Acinetobacter sp. was altered by growth on specific n-alkane carbon sources, the susceptibility to the granule fraction was also altered. Resistance to the activity of the granule fraction increased as the carbon chain length of the growth substrate increased. Liposomes formed from Acinetobacter sp. lipid extracts and containing glucose were made leaky with the addition of the granule fraction (boiled and not boiled), suggesting a membrane-disruptive activity of the granule protein against Acinetobacter sp. membranes.