Phospholipase and lysophospholipase activity of rat eosinophil leukocytes

Previous studies have shown the high lysophospholipase activity of rat eosinophilic leukocytes and used this enzyme to measure the rise in eosinophilic population of peripheral tissues caused by parasitic infections. This report details the methods and results of an investigation showing the presence in the same cells of high phospholipase (PLA) activity. Unfractionated and metrizamide-purified peritoneal eosinophil preparations were assayed using a mixed micelle substrate (6/15 mM lecithin/Triton X-100) at experimentally determined pH (6.4) and ionic strength (I=0.2) optima: the attendant reaction products included free fatty acids and organic P in a 2/1 molar proportion with a correspondent loss in the initial phospholipid concentration. The organic P fragment was further characterized as GPC (glycerylphosphorylcholine) by quantitative precipitation and acid hydrolysis. Estimates of PLA activity averaged 5 μmol/h/106 unfractionated eosinophils and metrizamide-purified eosinophil preparations. Paired tests for PLA and LysoPLA on unfractionated and enriched cell preparations, cytosolic extracts, and chromatographic fractions yielded similar activity ratios, supporting the inference of a close association of the two activities which could also be confirmed for the major tissues of eosinophil production and distribution.