Inhibition of polymorphonuclear leukocyte chemotaxis by the mucoid exopolysaccharide of Pseudomonas aeruginosa.

We tested the effect on human polymorphonuclear leukocyte (PMN) chemotaxis of the mucoid exopolysaccharide (MEP) elaborated by Pseudomonas aeruginosa strain P1M recovered from the sputum of a patient with cystic fibrosis (CF). A dose-related inhibition of chemotaxis under agarose was observed when mucoid exopolysaccharide at concentrations of 0.5 to 5.0 mg/ml was incorporated into the agarose. Similar inhibition was observed with the closely related polysaccharide alginic acid, but not with the neutral polymer Ficoll. The exopolysaccharide did not bind or inactivate the chemoattractant substance, nor was it toxic to PMN's. Digestion with alginase did significantly abrogate the inhibitory effect of alginic acid, but not of MEP. There was no difference in chemotaxis in the presence of the exopolysaccharide preincubated with heat-inactivated pooled antisera from CF patients chronically colonized with mucoid P. aeruginosa compared to MEP alone, or MEP preincubated with heat-inactivated pooled normal human sera. Inhibition of chemotaxis may represent yet another pathogenetic property of P. aeruginosa mucoid exopolysaccharide.