Simultaneous measurement of several cytokines using small volumes of biospecimens

The role of host immunity in the development of virus-induced cancers has been difficult to elucidate, in part because of our inability to effectively measure multiple immune parameters using available amounts of biological material. The objective of the present study was to validate the use of a newly developed multiplex assay, the LINCOplex assay, for the simultaneous measurement of multiple cytokines [interleukin/(IL)-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, IFN-gamma, and tumor necrosis factor-alpha]. Supernatants obtained from peripheral blood mononuclear cell cultures stimulated with various different mitogens and antigens (including phytohemagglutinin, influenza, tetanus, HPV16 E6 and E7 peptides, and media alone) were selected for study. In total, 750 specimens obtained from 26 participants were tested in replicate using the 8-plex LINCOplex assay (25 mul of specimen required per well). Every specimen was included in duplicate in a blinded fashion. For some specimens, multiple 2-fold dilutions of the same specimen were included to evaluate the linearity of results. The availability of independently obtained IL-2 and IFN-gamma results from standard single cytokine (simplex) assays allowed for a direct comparison between the LINCOplex results and those obtained from the simplex assays. Spearman correlation coefficients for continuous results, and exact agreement rates and weighted kappa statistics for quartiled variables, were computed to evaluate intra-and interassay agreement. IL-4 levels were consistently below the detectable level of the assay (3 pg/ml) whereas IL-6 and IL-8 levels were consistently above the highest detectable level of the assay (10,000 pg/ml), and these three cytokines were, therefore, not evaluated further. For the remaining five cytokines, excellent intra-assay reproducibility was observed, with Spearman correlation coefficients consistently above 0.90 for all five cytokines. Exact agreement rates ranging from 77.6-90.3% and weighted kappas ranging from 0.81-0.92 were observed. Similar results were observed when analysis was restricted to supernatants obtained from cultures that had been stimulated with HPV16 peptides and when analysis was restricted to supernatants obtained from cultures containing no antigen or mitogen, suggesting that the LINCOplex assay is applicable under conditions where moderate or weak cytokine responses/levels are expected. Linearity of results was observed when dilutions of a single specimen were blindly tested, with the exception of IL-2 and IL-10, where deviations from linearity were sometimes observed. For IL-2 and IFN-gamma, where results from simplex assays were available for comparison, the LINCOplex assay and the simplex assay results agreed well. Spearman correlation coefficients were 0.86 and 0.93 for IL-2 and IFN-gamma, respectively. Exact agreement and weighted kappa values were 68.5% and 0.72 (95% confidence interval, 0.65-0.79), respectively, for IL-2 and 67.3% and 0.73 (95% confidence interval, 0.67-0.80), respectively, for IFN-gamma. These results indicate the applicability of the LINCOplex assay for the simultaneous measurement of multiple cytokines using small amounts of biological material.