Measurement of CFI bioactivity.

CFI bioactivity can be measured in plasma samples using an adapted assay that uses diluted plasma as the source of CFI. CFI bioactivity is temperature sensitive as heating the samples to 60° C abolishes the ability of the sample to generate iC3b (green symbol). Under the configuration of the assay, one can estimate the concentration of plasma that achieve half the amount of iC3b (i.e., 2.3 nl). We define this volume as 1 mU of CFI bioactivity. CFI bioactivity can be measured by determining the concentration of CFI protein in the same sample with an ELISA and correct the activity values by the amount of protein present in the sample, hence CFI bioactivity per unit of protein.