Effects of ageing on generation of ED2(high) major histocompatibility complex class II+ macrophages during cold stress

The effects of cold stress (5 degrees C, 24 h) were investigated on the fun ction 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 exa mined. The proportion of cells with a high density of ED2 (ED2(high) cells) , expressing major histocompatibility complex (MHC) class II molecules, was significantly increased in peritoneal cells during cold stress in young, b ut not in old, rats. Antigen-presenting function was significantly higher i n ED2(high) cells than in cells with a low density of ED2 (ED2(low) cells), thereby indicating that ED2(high) cells are at a functionally high level. While serum corticosterone concentration in old rats increased markedly aft er 3 h of cold stress, that in young rats did not vary substantially, and w as followed by a significant decrease in both groups of rats after 24 h of cold stress. Administration of dexamethasone to young rats completely inhib ited the increase of ED2(high) cells caused by cold stress. Meanwhile, the proportion of ED2(high) cells in young rats was significantly increased by adrenalectomy. Furthermore, nuclear translocation of a large amount of the GC receptor was observed in ED2(low) cells. These results suggest that cold s stress enhances immune function in young rats, but not in old rats, and t hat the generation of ED2(high) cells are partly regulated by circulating G C level.