Specific binding of HNP-1 to C1q. A fixed concentration of HNP-1^Biotin was incubated with increasing concentrations of either unlabelled HNP-1 (▪) or Protamine (▴) for 30 minutes at 4°C, and then added to microtiter wells that were coated with 1 μg C1q. After incubation, bound HNP-1^Biotin was detected as described. The optical density was measured and compared with binding of HNP^Biotin that was not preincubated. The percentage inhibition of binding induced by HNP or protamine is depicted.