DUAL EFFECTS OF FORMYLPEPTIDES ON THE ADHESION OF ENDOTOXIN-PRIMED HUMAN NEUTROPHILS

Neutrophils, treated with sequential additions of bacterial products s uch as endotoxin (E. Coli lipopolysaccharide, LPS) and the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP), undergo to me tabolic activation and express membrane-anchoring proteins that promot e adhesion to serum-coated culture wells. By investigating the dose-re sponse relationships of these phenomena, we have found that: (a) resti ng neutrophils do not produce a significant amount of superoxide (O-2( -)) and show only minimal adhesion to serum-coated plastic surfaces; ( b) fully activatory doses (> 5 x 10(-8)M) of fMLP induce the release o f O-2(-) and a significant increase of the cell adhesion; (c) pretreat ment of the cells for 1 h with LPS augments cell adhesion to serum-coa ted culture wells in the absence of further stimulation and primes the neutrophils to enhanced fMLP-dependent O-2(-) release; (d) addition o f low, substimulatory doses of fMLP (from 10(-10)M to 5 x 10(-9)M) inh ibits and reverses the adhesion of LPS-treated cells, (e) high fMLP do ses (> 10(-7)M) are additive to LPS in promoting adhesion. Phorbol-myr istate acetate(> 10(-9)M) increased adhesion in both normal and LPS-tr eated neutrophils, but low doses of this stimulant did not inhibit adh esion. Low doses (10(-9)M) of fMLP increased intracellular cyclic AMP in both normal and LPS-treated neutrophils, suggesting that stimulus-i nduced rises in cAMP may be the negative signal responsible for down-m odulation of adhesion. Low (5 x 10(-9)M) and high (5 x 10(-7)M) fMLP d oses induced the same increase of expression of CD11/CD18 integrins, i ndicating that the inhibition of adhesion caused by low doses is not d ue to quantitative down-regulation of integrins. These findings may pr ovide an in vitro model of the complex biological events involved in t he regulation of neutrophil adhesion.