Anti-C1q column: ligand specific purification of immune complexes from human serum or plasma. Analysis of the interaction between C1q and immune complexes.

An efficient and reproducible procedure has been developed for the specific isolation of immune complexes. PEG precipitation of EDTA serum or plasma was an essential preliminary step to separate complex-bound from free Clq. PEG had no discernible effect on the molecular weight size of the extracted complexes. Redissolved complexes were incubated with a Sepharose-4B column coated with anti-human Clq antibodies and following removal of unbound material the bound complexes were sequentially eluted with 0.02 M EDTA, 0.5 M NaCl and 1 M propionic acid. Characteristics of the affinity column were established by the purification of ¹²⁵I-labelled BSA-anti-BSA complexes and heat-aggregated IgG (HAGG) incubated in normal human scrum (NHS), EDTA and NaCl eluted complexes were of similar molecular size and contained antigen, specific antibody, as well as human IgM, IgG, albumin, C3, C3c, C3d and Clq. Acid eluted complexes contained the highest yield of specific antigen and antibody and comprised in addition human Clq and C3d. Activation of complement components after Clq made the bond between Clq and immune complexes resistant to 0.5 M NaCl and interfered with the binding between solid phase anti-Clq and complex bound Clq. Using BSA-anti-BSA complexes and HAGG activated in NHS it was apparent that only a minority of the complexed material was isolated via the Clq ligand and this probably applies to the Clq binding assay. Most complexed material could be isolated using an anti-C3 affinity column. [ABSTRACT FROM AUTHOR]