Estimation of variability in the assay of human interleukin-1

The variability in measurements of the interleukin-1 (IL-1) responsiveness of human monocyte (M phi)-depleted mononuclear cells (MDC) and in IL-1 production of human M phi has been estimated. Subjects were grouped so that inter- and intra-donor biological variability were evaluated, as well as day-to-day and basic intrinsic test-to-test methodological variability. IL-1 responsiveness was measured by the co-mitogenic effect of unstimulated and LPS-stimulated IL-1 standards on the PHA-induced proliferation of MDC. IL-1 production was measured by the enhancing effect of unstimulated and LPS-stimulated M phi-culture supernatants on PHA-stimulated allogeneic MDC. The variability of the IL-1 responsiveness of MDC was influenced mainly by biological factors, and this variability was effectively reduced by calculating the difference between the response of unstimulated and stimulated cultures, or by using cryopreserved MDC originating from a single stock of cells. In contrast, IL-1 production from both unstimulated and LPS-stimulated M phi was subjected to less biological and methodological variability, and this variability was not reduced by the above mentioned procedures. The results indicate that when assaying IL-1 production in clinical investigations involving longitudinal or comparative studies, a test system consisting of cryopreserved MDC from one stock of cells should be used. Alternatively the difference between the IL-1 activity from unstimulated and LPS-stimulated cultures should be calculated, since these procedures enhance the reproducibility of the measurements.