Selective losses of large immune complexes during density gradient ultracentrifugation and an approach for prevention of these losses.

Substantial amounts (12.3-40.0%) of model immune complexes became nonspecifically adsorbed to centrifuge tubes during sucrose density gradient ultracentrifugation, and the adsorbed complexes were therefore unavailable for subsequent detection by the C1q solid-phase assay. The adsorption was greater for heavier immune complexes; thus detection of large-latticed complexes was impaired more than detection of small-latticed complexes. Loss of complexes could be prevented by incorporation of 0.05% polyoxyethylene (20) sorbitan monolaurate (Tween 20) into sucrose density gradient solutions and precoating tubes with gelatin. Tween 20 did not alter the immune complex lattice and did not prevent detection of immune complexes by the C1q solid-phase assay. Similar selective losses of immune complexes occurred when serum specimens from 2 patients with circulating immune complexes were analyzed by sucrose density gradient ultracentrifugation; the nonspecific adsorption of serum immune complexes which occurred during ultracentrifugation could be prevented by precoating centrifuge tubes with gelatin and incorporating 0.05% Tween 20 into sucrose gradients.