Effects of Cold Stress, Corticosterone and Catecholamines on Phagocytosis in Mice: Differences between Resting and Activated Macrophages

OBJECTIVE: We subjected mice to acute cold stress and studied the effect on phagocytosis by peritoneal macrophages mediated by 3 types of phagocytic receptors: Fcgamma, complement receptors 3 (CR3) and mannose and beta-glucan receptors. METHODS: Mice were subjected to a cold stress condition (4 degrees C for 4 h), and then peritoneal macrophages were harvested and phagocytosis assays performed in vitro. RESULTS: We found a striking difference between resting and lipopolysaccharide (LPS)-activated macrophages (by intraperitoneal injection of LPS 4 days before the stress experiment): for resting macrophages cold stress caused a decrease in phagocytosis mediated by Fcgamma or mannose receptors, while for activated macrophages we observed an increase in phagocytosis by the 3 types of receptors. These effects were associated with an increase in plasma concentrations of corticosterone and catecholamines following the cold stress. In order to verify whether these hormone changes could account for the observed effects on phagocytosis, we performed in vitro assays by incubating macrophages harvested from nonstressed animals with these hormones for 4 h at 37 degrees C and measuring their phagocytic capacity. The following experiments were done: (a) with resting (nonactivated) macrophages; (b) with macrophages previously activated in vitro by incubation with LPS; (c) with macrophages previously activated in vivo by intraperitoneal injection of mice with LPS, 4 days before harvesting the cells. We found that for resting macrophages, corticosterone decreased phagocytosis mediated by Fcgamma and mannose and beta-glucan receptors, but catecholamines had no effect. For macrophages activated either in vivo or in vitro, catecholamines caused an increase in phagocytosis (excluding mannose receptors) while corticosterone had no effect. CONCLUSION: The above findings suggest that stress can regulate phagocytosis in different ways, depending on the kind of phagocytic receptor involved, the level of stress hormones and the physiological state of the macrophages.