Isolation of C1q-binding immune complexes by affinity chromatography and desorption with a diaminoalkyl compound.

The applicability of affinity chromatography to the isolation of C1q-binding immune complexes (IC) in sera was explored. Purified human C1q was covalently coupled to agarose or adsorbed to IgG-agarose resins. Sera containing preformed virus-antibody complexes or rheumatoid arthritis (RA) sera were passed through the columns and C1q-bound IC, eluted off with 1,4-diaminobutan at mild basic conditions, were analysed by immunodiffusion, crossed immunoelectrophoresis, gel filtration and electron microscopy. Under conditions of antibody treatment which caused almost 100% inhibition of virus plaque formation, about 30% of formed 14C-labelled equine arteritis virus-antibody complexes was bound specifically to and desorbed from C1q-IgG agarose columns. Studies with RA-sera indicated the presence of both IgM-IgI and intermediate size IgG, C1q-binding, complexes in 3 out of 5 tested seropositive sera. In two sera only intermediate size IC were demonstrable. The results obtained in these two IC model systems suggested that the described methods could be useful for isolation of C1q-binding IC in general.