Fixation of human or rat C3b on human or rat C-reactive protein (CRP) onto an enzyme-linked immunosorbent assay (ELISA) plate. ELISA plates were coated with human (a) or rat (b) CRP at 10 µg/ml (⋄), or with buffer (▴), and incubated with increasing volumes (0 to 3·33 µl) of human or rat plasma. Then, C3b/c fixation on CRP was detected with specific monoclonal antibody (mAb), as described in the Materials and methods. This figure is representative of three experiments, with similar results obtained on each occasion.