Lipopolysaccharides from periodontal pathogens prime neutrophils for enhanced respiratory burst: differential effect of a synthetic lipid a Precursor IV_A(LA‐14‐PP)

When neutrophils are incubated with bacterial lipopolysaccharide (LPS), they become primed for enhanced release of superoxide anion (O₂⁻) in response to stimulation by FMLP. We investigated the human neutrophil‐priming activity of LPS from the periodontal pathogens, Porphyromonas gingivalis (Pg), Prevotella intermedia (Pi) and Actinobacillus actinomycetemcomitans (Aa) in comparison with that of LPS from Escherichia coli (E. coli). The optimum conditions for LPS to prime neutrophils were assessed for every LPS and found to be as follows: Neutrophils were incubated with LPS in the presence of 10% heat‐inactivated plasma and 1 mM EDTA at 37°C for 30 min and then stimulated with 1 μM FMLP at 37°C for 7 min. Under these conditions, half‐maximum priming was observed at 6.2 ng/ml Pg‐LPS, 45 ng/ml Pi‐LPS, 1.5 ng/ml Aa‐LPS and 1.5 ng/ ml E. coli‐LPS. The priming activity of each LPS was neutralized by polymyxin B. Anti‐CD14 monoclonal antibody inhibited priming by all LPS. The priming by Aa‐LPS and E. coli‐LPS was inhibited by LA‐14‐PP, a synthetic lipid A precursor IV_A, but that by Pg‐LPS and Pi‐LPS was not. Priming by tumor necrosis factor alpha was not affected by polymyxin B, anti‐CD14 antibody or LA‐14‐PP. Gelation of Limulus amebocyte lysate occured at 10 pg/ml Pg‐LPS, 30 pg/ml Pi‐LPS, 3 pg/ml Aa‐LPS and 3 pg/ml E. coli‐LPS. Thus LPS from different periodontal pathogens primed neutrophils with different efficacy. The difference in the sensitivity to LA‐14‐PP among the four LPS tested raises the possibility that the mechanism of host response to Pg‐LPS or Pi‐LPS may be different from that to Aa‐LPS or E. coli‐LPS.