MENSTRUAL-DEPENDENT AND GENDER-DEPENDENT VARIATIONS IN CIRCULATING IL-1 AGONISTS, ANTAGONISTS, AND BINDING-PROTEINS

This study tested the hypotheses that sex-related differences in circu lating binding proteins for interleukin-1 beta (IL-1 beta) exist and t hat these binding proteins affect immunoassays for IL-1 beta and IL-1R a, I-125-labeled IL-1 beta was added to human plasma samples, then chr omatographed. The percentages of total radioactivity eluting in a high -molecular-weight peak were 21.0 + 0.8 for men (n = 6), 19.1 +/- 0.9 f or follicular phase women (n = 6), and 18.0 +/- 0.8 in luteal phase wo men (n = 6; men vs, women, P = 0.032; follicular vs. luteal, P = 0.035 ), and correlated with plasma sIL-1RII concentrations (r = 0.647, P = 0.001). Plasma IL-1 beta immunoreactivity did not correspond to concur rent cellular secretion rates due, in part, to interference in the IL- 1 beta assay by sIL-1RII, Correspondence between plasma IL-1Ra levels and cellular secretion rates was observed only after serial dilutions of the samples, These results indicate that plasma IL-1 beta binding c apacity differs between men and women and that sIL-1RII is a major con tributing factor. Furthermore, relating plasma IL-1 isoform immunoreac tivity to functional measures (tracer binding) or concurrent release b y isolated cells can lead to insights about assay interferences that m ay exist in plasma.