Deactivation of human neutrophil chemotaxis by chemoattractants: effect on receptors for the chemotactic factor f-Met-Leu-Phe.

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Abstract
Normal human peripheral blood PMN were exposed to varying concentrations of partially purified chemotactic complement fragments (C5fr) and a chemotactic peptide N-formyl methionylleucylphenylalanine (f-Met-Leu-Phe). This exposure resulted in a decreased chemotactic response termed deactivation of chemotaxis. Deactivation was found to be nonpreferential for the deactivating stimulus when high concentrations of either f-Met-Leu-Phe (10(-6) M) or C5fr (20 micrograms/ml) were used. When PMN were incubated with lower concentrations of C5fr (10 micrograms/ml), there was preferential deactivation towards C5fr. Similarly, preferential deactivation of chemotaxis was observed when PMN were incubated with 10(-6) M f-Met-Leu-Phe, but this was transient and cells were nonpreferentially deactivated 60 min after the initial exposure to f-Met-Leu-Phe. The availability of receptors for tritiated f-Met-Leu-Phe was examined by Scatchard analyses and measurement of reversible f-Met-Leu-[3H]Phe binding to C5fr and f-Met-Leu-Phe-deactivated PMN. When PMN f-Met-Leu-Phe receptors were studied immediately after exposure to concentrations of C5fr causing either preferential or nonpreferential deactivation, there was increased receptor availability compared with control PMN. In contrast, PMN deactivated with high concentrations of f-Met-Leu-Phe 10(-6) M) had a transient decrease in the number of receptors followed 1 hr later by an increase in the number of receptors. This was similar to the functional correlate of preferential deactivation of chemotaxis immediately after incubation with f-Met-Leu-Phe followed by nonpreferential deactivation in these same PMN. The data indicate that preferential deactivation of chemotaxis may be associated with a preferential decrease (down-regulation) of chemoattractant receptors and that nonpreferential deactivation is associated with an increase in chemoattractant receptors.