EFFECTS OF SODIUM CONCENTRATION ON HUMAN NEUTROPHIL BACTERICIDAL FUNCTIONS

What are the ionic requirements for neutrophil (PMN) function and how might altered electrolyte concentrations contribute to airway disease? The in vitro killing of Pseudomonas aeruginosa by human peripheral wh ite blood cells (WBCs) was progressively compromised as Na+ concentrat ion was lowered from 124 to 62 mM; at 62 mM Na+, bactericidal activity was 28.8 +/- 7.4% (SE) of normal. In contrast, Cl- concentration affe cted killing only when lowered to 8 mM. We examined phagocytosis and o xidative metabolism in response to P. aeruginosa or particles opsonize d with either immunoglobulin G (IgG) or complement (C'). Phagocytosis of P. aeruginosa and of IgG-coated particles was Na+-dependent (31.2 /- 3.1 and 58.6 +/- 14.2% of normal, respectively, at 62 mM Na+). Howe ver, no effect on uptake of C'-coated particles was observed, and the respiratory burst at 70 mM Na+ was normal regardless of stimuli. Thus low Na+ concentration compromises select PMN functions. These results may help explain why airways of cystic fibrosis (CF) patients become c olonized with bacteria such as P. aeruginosa. Perhaps the low concentr ation of Na+ reported for some CF respiratory secretions inhibits bact ericidal functions of PMNs, predisposing these patients to airway infe ctions.