Capture antibodies screened for IL-6 capture in combination with four different detection antibodies. Each candidate antibody was used as a capture antibody to assess 125 pg ml–1 human recombinant IL-6. Detection antibodies from commercially available ELISA kits were used to determine which antibody pair would result in the best detection of IL-6 in human serum. The approach was repeated for human plasma samples, with similar results (data not shown). IL-6, interleukin 6; ELISA, enzyme-linked immunosorbent assay; OD, optical density; mAb, monoclonal antibody; det Ab, detection antibody; Det Ab-1, Det Ab-2, Det Ab-3, Det Ab-4