HOMOLOGOUS PRIMING IN CHEMOTACTIC PEPTIDE-STIMULATED NEUTROPHILS

The kinetics and dose-dependence of activation of human neutrophils ex posed to sequential additions of the chemotactic peptide n-formyl-meth ionyl-leucyl-phenylalanine (fMLP) have been investigated by multiwell microplate assays. Treatment of neutrophils with medium-high doses (fr om 10(-8) to 5 x 10(-7) M) of fMLP caused activation of superoxide ani on (O2-) production, but prevented further activation by a subsequent addition of an optimal dose (from 10(-7) M to 5 x 10(-7) M) of fMLP. T hese findings represent an example of cell desensitization, or adaptat ion. However, neutrophils treated with low, sub-stimulatory doses (fro m 10(-10) to 5 x 10(-9) M) of the peptide and then treated with optima l doses of fMLP exhibited an O2- production that was two to three-fold higher than that induced by the same optimal doses on untreated cells . A similar phenomenon of homologous priming of the oxidative metaboli sm of neutrophil has not previously been described or characterized. P riming was maximal after about 30 min of incubation with fMLP, which d iffered from desensitization, which required only a few minutes. Homol ogous priming was not confined to O2- production, but was also observe d with the release of the granule enzyme, lysozyme. Low doses of fMLP were also capable of triggering an increase of intracellular free Ca2 and of fMLP membrane receptors, which are possible mechanisms respons ible for priming.