Kinetics of Macrophage Recruitment and Turnover in Peritoneal Inflammatory Exudates Induced by Salmonella or Thioglycollate Broth

Kinetics of peritoneal macrophage turnover during infection of mice with Salmonella enteritidis or following injection with thioglycollate broth or other peritoneal stimulants has been studied. Single intravenous injections of tritiated thymidine were given and the cells were examined by autoradiography. Maximum labelling of small adherent peritoneal macrophages occurred when 3 H‐thymidine was given 1 d after Salmonella and the cells were harvested 1 d later. Labelled cells decreased at later times despite maintenance of high numbers of macrophages in the exudates. Results from experiments in which labelled peritoneal cells were reinjected indicated that small, monocyte‐enriched, labelled cells were not the major source of the large macrophages. Similar labelling at 2 d was observed using heat‐killed Corynebacterium parvum or lipopolysaccharide (LPS) as ip stimulants. Following injection of thioglycollate broth, labelled peritoneal macrophages were only detectable if 3 H‐thymidine was given before the stimulant. These labelled cells remained longer in the peritoneal cavity. Labelling of and numbers of blood monocytes were consistent with the promotion of monocytopoiesis by Salmonella but not by thioglycollate. The response to thioglycollate but not Salmonella was dependent on the age of the mice. Animals injected with thioglycollate 1 d before Salmonella also had decreased resistance to bacteria and low numbers of labelled peritoneal macrophages. We propose that thioglycollate may recruit from a subset of preformed monocytes and temporarily block monocytopoiesis or macrophage bactericidal activity.