Multiple interleukin-1 activities in luteal phase human plasma

Correlation of IL-1 levels in the human circulation with various physiological and pathological conditions has been hampered by substances in whole plasma or serum which interfere with the in vitro lymphocyte activation assay. Chromatography over G-50 separates most of the interfering factors from IL-1 activity found in the 4-15 kD molecular weight range. Using this method, IL-1 activity was found consistently in plasma from women in the luteal phase of their menstrual cycle. This investigation provides further evidence that the activity is attributable to IL-1 by demonstrating that whole plasma injected into rats reduced their plasma iron levels and that plasma fractions which activated thymocytes also caused fever when injected into mice.