The objective of this study is to investigate the role of the gut microbiota in the systemic priming of immune effector cells. Twelve healthy male volunteers, 18-35 years of age, will be treated with broad spectrum antibiotics (ciprofloxacin, vancomycin, metronidazole) for seven days, in order to deplete the gut microbiota. Blood and faeces will be sampled before, 24 hours and 6 weeks after the 7-day period of antibiotics. Main study endpoints include laboratory parameters for inflammatory responses, functional assays (ex vivo stimulation assay) and gut microbiota composition.