Fig. 6.

CRP binds IL-6 without interfering with its biological activity. (a) IL-6 is coimmunoprecipitated with CRP. Recombinant human IL-6 (500 ng) was incubated with an anti-CRP polyclonal antibody conjugated to Protein A-Sepharose in the absence (lane 2) or in the presence of 5 µg of human purified CRP (lane 3). Lane 1 shows recombinant human IL-6. The immunoprecipitates were subjected to SDS-PAGE and Western Blotting, and the presence of IL-6 was revealed with a mAb to hIL-6. MWM, molecular weight markers. (b) CRP does not affect the biological activity of IL-6 on XG-1 cells. A control human serum was preincubated with rhIL-6 (100 pg/ml) for 1 h at 37°C in the absence or in the presence of human purified CRP (100 µg/ml) and then tested on the XG-1 cells. Results are expressed as mean + SE, represent by the vertical bars, of triplicate determinations. (c) CRP does not affect the binding of the IL-6/sIL-6R complex to gp130. rhIL-6 (5 ng/ml) was added to a normal control serum in the absence or in the presence of exogenous CRP (100 µg/ml) and then tested in the IL-6/gp130 binding activity assay. Results are expressed as mean + SE, represent by the vertical bars, of triplicate determinations.