Suboptimal C3b/C3bi deposition and defective yeast opsonization. II. Partial purification and preliminary characterization of an opsonic co-factor able to correct sera with the defect.

Using a correction assay a factor essential for normal deposition of C3 fragments on zymosan was identified in fractions of serum obtained by Sephacryl S-300 gel filtration (eluting between IgG and albumin), preparative Pevikon block electrophoresis (eluting in the beta-region) and DEAE-ion-exchange chromatography (eluting immediately post IgG). Active material was also identified in a commercial preparation of transferrin. A combination of DEAE-ion-exchange chromatography and gel filtration was used to partially purify the co-factor. The factor has an approximate relative molecular mass of 70,000-80,000.