Neutrophil priming by lipopolysaccharide involves heterogeneity in calcium-mediated signal transduction. Studies using fluo-3 and flow cytometry.

Abstract

Bacterial LPS is known to prime neutrophils for enhanced responses to subsequent stimulation by agonists such as FMLP. The purpose of this study was to determine whether priming is due to a uniform enhancement of function in all cells or to a recruitment of previously unresponsive neutrophils. Results from initial experiments confirmed the findings of other investigators and served to validate our methodology. We demonstrated that LPS-primed neutrophils had: 1) augmented superoxide anion production after FMLP or PMA stimulation; 2) increased FMLP-induced f-actin formation; 3) enhanced surface expression of CD11b, CD14, and the FMLP receptor; 4) caused higher baseline concentrations of intracellular calcium ([Ca2+]i); 5) caused greater elevations of [Ca2+]i after FMLP stimulation; and that 6) the priming effect of LPS on superoxide anion production and f-actin polymerization could be blocked by the [Ca2+]i chelator bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid. In subsequent experiments, we determined that at low concentrations of FMLP, LPS augmented the overall responsiveness of a population of neutrophils by causing a subpopulation of cells to become highly responsive and able to generate changes in [Ca2+]i upon low level stimulation. Heterogeneity in calcium-mediated signal transduction among neutrophils may be important in the fine control of the nonspecific immune system in response to weak environmental signals.