Interaction of purified leukocidin from Pseudomonas aeruginosa with Bovine polymorphonuclear leukocytes

The interaction of purified leukocidin from Pseudomonas aeruginosa, strain 158, with polymorphonuclear leukocytes of cattle (PMLC) was studied by using 125I-labeled toxin. According to the Scatchard plot, PMLC offered two binding sites for leukocidin: one at the surface of the plasma membrane, and a second one that presumably became accessible to the toxin in the course of the cytotoxic action. Toxin once fixed to PMLC at 37 C could not be detached from the cells by either chemical or mechanical treatment. However, active leukocidin was liberated if it was bound to PMLC at 4 C and the temperature of the cell suspension was subsequently increased to 37 C. In the presence of Ca2+, the velocity of toxin fixation was accelerated and the rate of fixation was increased. Preliminary investigations on the identification of the leukocidin-binding material indicated the leukocidin receptor to be an integral protein of the plasma membrane.