Effects of ageing on generation of ED2high major histocompatibility complex class II+ macrophages during cold stress

The effects of cold stress (5 degrees C, 24 h) were investigated on the function and surface phenotype of peritoneal cells in the monocyte/macrophage lineage from young (8-10-week-old) and old (22-24-month-old) rats. The role of glucocorticoid (GC) in the immunomodulation by cold stress was also examined. The proportion of cells with a high density of ED2 (ED2high cells), expressing major histocompatibility complex (MHC) class II molecules, was significantly increased in peritoneal cells during cold stress in young, but not in old, rats. Antigen-presenting function was significantly higher in ED2high cells than in cells with a low density of ED2 (ED2low cells), thereby indicating that ED2high cells are at a functionally high level. While serum corticosterone concentration in old rats increased markedly after 3 h of cold stress, that in young rats did not vary substantially, and was followed by a significant decrease in both groups of rats after 24 h of cold stress. Administration of dexamethasone to young rats completely inhibited the increase of ED2high cells caused by cold stress. Meanwhile, the proportion of ED2high cells in young rats was significantly increased by adrenalectomy. Furthermore, nuclear translocation of a large amount of the GC receptor was observed in ED2low cells. These results suggest that cold stress enhances immune function in young rats, but not in old rats, and that the generation of ED2high cells are partly regulated by circulating GC level.