Isopycnic ultracentrifugation of immune complexes.

Isopycnic ultracentrifugation is frequently applied for preparative isolation of macromolecules. Using bovine serum albumin (BSA)-anti-BSA antibody complexes as a model system, isopycnic banding of complexes was observed in CsCl, Nycodenz, and sucrose gradients. In CsCl gradients, free antigen or antibody could not be separated from the immune complexes. Variations in antigen to antibody ratio from equivalence and in the amount of complement present during complex formation resulted in zone broadening and banding at slightly lower densities in Nycodenz. This was not observed in sucrose. Serum immune complexes were isolated from patients with rheumatoid arthritis or ankylosing spondylitis. Banding of in vivo-formed immune complexes was observed more frequently in sucrose than in Nycodenz.