Increased urine interleukin-1 levels in aging

Our laboratory previously noted an increase in thymocyte mitogenic activity in the urine of many elderly patients. The present study was performed to verify this finding and to determine if this activity was actually due to an increase in interleukin-1 (IL-1). IL-1 levels were measured in the urine of 33 healthy, ambulatory, elderly subjects (ages 83-95 years), using both a murine thymocyte bioassay, measuring activation by the incorporation of tritiated thymidine and an MTT dye reduction assay. There was a significant increase in urine IL-1 in 85% of elderly individuals. In the MTT dye reduction assay, mean elderly urine IL-1 levels were 0.88 U/ml, in comparison with a young control group (ages 23-37 years) in which urine IL-1 levels were very low (mean IL-1 < or = 0.05 U/ml). Urine levels of IL-1 beta were also measured by using a sensitive immunoassay (ELISA) and were found to be significantly increased in the elderly (mean = 57.4 pg/ml), compared to the young (mean = 2.5 pg/ml). In contrast, IL-2 levels in urine were very low, with no difference between the young and the elderly. Mean urine protein and creatinine levels did not differ significantly between young and old, and did not account for the increase in urine IL-1 levels. Although its immunologic significance is not yet understood, this striking increase in IL-1 is an unusual and interesting finding that merits further investigation.