Development and applications of a radioimmunoassay (RIA) for the in vitro and in vivo quantification of murine IL-1 beta.

A specific, precise, and accurate radioimmunoassay (RIA) for murine interleukin-1 beta (mIL-1 beta), with a sensitivity of 250 pg/ml, has been established. Although mIL-1 beta shares structural homology and multiple biological properties with mIL-1 alpha, this RIA did not detect mIL-1 alpha or other murine cytokines such as TNF and IL-6. Recombinant mIL-1 beta, freshly added in different concentrations to murine plasma, was recovered from 88 to 104%, and intra- and interassay coefficients of variation never exceeded the 10% value. Parallel analysis showed that murine plasma and cell or organ supernatants did not affect the test. This characteristic allowed mIL-1 beta analysis directly in the nonmanipulated biological specimens. In murine macrophage supernatants collected after 24 h of in vitro stimulation with LPS, nanogram fractions of IL-1 beta were detected by RIA. These values corresponded to approximately 50% of the total IL-1 detected by the LAF bioassay. In spleen, liver, and lung, IL-1 beta appeared at significant levels (110 ng/g of lung, 638 ng/g of spleen, and 78 ng/g of liver) as early as 1 h after LPS administration, reached the plateau 1-2 h later, and then slowly but progressively decreased. In plasma and brain, nanogram fractions of IL-1 beta were detectable by 4 h post-LPS. Thereafter, IL-1 beta levels progressively increased to reach the value of 44 ng/g in the brain and 2 ng/ml in plasma 8 h after LPS treatment.