Recently we found that certain antibiotics which are markedly concentrated by human polymorphonuclear leukocytes (PMN) failed to kill susceptible, intraphagocytic Staphylococcus aureus, even though cellular drug levels were quite high. The possibility that specific antibiotics might adversely affect phagocyte antibacterial function was considered. Thus, we studied the effects of multiple antibiotics and adenosine, a known modulator of the PMN respiratory burst response, on neutrophil antibacterial function. At nontoxic concentrations, these drugs had no effect on degranulation in stimulated PMN. Adenosine was a potent inhibitor of formyl-methionyl-leucyl-phenylalanine (FMPL)-stimulated superoxide and hydrogen peroxide generation in PMN but produced less inhibition of microbial particle-induced respiratory burst activity. Three of the tested antibiotics, all of which reach high concentrations in phagocytic cells, had a marked modulatory effect on the PMN respiratory burst. Clindamycin, which enters phagocytes by the cell membrane adenosine (nucleoside) transport system, had only a modest effect on FMLP-mediated superoxide production but inhibited the microbial particle-induced response by approximately 50%. Roxithromycin and trimethoprim were efficient inhibitors of PMN superoxide generation stimulated by FMLP and concanavalin A (also inhibited by erythromycin) but had less effect on zymosan-mediated respiratory burst activity. Antibiotics which entered phagocytes less readily had no effect on the respiratory burst response in PMN. These results, as well as those of experiments with inhibitors of cell membrane nucleoside receptors, indicated that the antibiotic effect is mediated through intraphagocytic pathways. The possibility that antibiotic-associated inhibition of the PMN respiratory burst response might alter leukocyte antimicrobial and inflammatory function deserves further evaluation
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