Microtiter plates were coated with various purified human complement proteins or BSA as a negative control and incubated with 20 µg/ml SMSB3 (A) or SMSB4 (B). Bound serpins were detected using specific polyclonal antibodies against SMSB3 and SMSB4. Shown are means ± SEM of n = 3 independent experiments. The statistical significance of differences between BSA and the rest of the data groups was estimated using one-way ANOVA. *, p<0.05; **, p<0.01; ***, p<0.001. Grey, serine proteases; black, other complement factors. C Direct binding of complement factors from NHS to SMSs. Increasing concentrations of NHS were added to wells coated with SMSB3 (▾, black), SMSB4 (•, grey) or BSA as a negative control (○, white) and bound complement factors were detected by specific antibodies. Shown are means ± SEM of n = 3 independent experiments measured in duplicates. NHS was tested from 0–100%. Positive controls were used for complement proteins, where no binding to the SMSs was detectable confirming strong immunodetection of the complement factor on 1% NHS coating.