Reactivity of FI-deficient patient’s serum with goat anti-human FI. Proteins in NHS, FI-depleted serum, and the Pt. serum, all at a final dilution of 1:100 in 4× LDS sample buffer (either nonreduced or reduced with 10% ß-mercaptoethanol), were separated on a 4–12% Bis-Tris gel and probed with goat polyclonal anti-FI antibody followed by ALP-conjugated anti-goat IgG. Asterisks highlight detection of FI (combined heavy and light chains in nonreduced samples, heavy and light chains in reduced samples) in NHS and absence in FI-depleted serum and the patient’s serum. A third parallel section of the membrane (nonreduced samples) was probed with the secondary antibody (ALP-conjugated anti-goat IgG) only. All sections of the blot were exposed to substrate for the same length of time. MW, molecular weight marker (kDa); Pt. serum, patient’s serum. Source data are available for this figure: SourceData F3.