Effects of β₂-agonist administration on bacterial phagocytosis by splenic macrophages in Mice

We examined the effects of 6-week daily administration of an anabolic dose of a β₂-agonist clenbuterol (1.0 mg/kg body weight/day) on the phagocytic capacity of splenic macrophages of 5-week-old male C57BL/6 J mice against Escherichia coli. After 24 h of cessation of clenbuterol or vehicle administration, splenic adherent cells were isolated and analyzed by flow-cytometry. The cells were separated into three subpopulations based on their size. The isolated cells included small cells, which expressed markedly higher levels of macrophage receptor with collagenous structure. Furthermore, these cells exhibited higher phagocytic capacity against E. coli when compared to other subpopulations. The phagocytic capacity of the small cells was clearly suppressed after clenbuterol administration. These results suggest that chronic utilization of clenbuterol as a doping drug impairs bacterial clearance mediated by highly phagocytic splenic macrophages.