Covalently cross-linked immune complexes prepared with multivalent cross-linking antigens

Abstract

Covalently cross-linked immune complexes were prepared with multivalent antigens, obtained by coupling varying numbers of 4-azido-4-nitrophenyl groups (NAP) on human serum albumin as the carrier molecule (NAPn . HSA). In this system the haptenic group served to bind the antigen to the antibody (antibodies to NAP) and to form covalent bonds upon photoactivation. The covalently cross-linked immune complexes contained around 30% of antibodies that were dissociable from complexes by SDS polyacrylamide gel electrophoresis. A comparable portion of antibody-combining sites were accessible to the free hapten (NAP . lysine) in molar excess by equilibrium dialysis. The stable, covalently cross-linked complexes with NAP7.0 . HSA and NAP12.9 . HSA were prepared and separated into complexes with varying degrees of lattice by sequential steps of gel filtration. Ag1Ab1 complexes were obtained with reasonable homogeneity. Other preparations contained successively higher lattices but were not homogeneous. When these complexes were injected into mice, the increasing lattice of complexes resulted in increasingly rapid removal of the complexes from the circulation. The antigen, independent of lattice, also contributed to removal of complexes from circulation. NAP12.9 . HSA alone was removed from circulation faster than NAP7.0 . HSA, and Ag1Ab1 complexes with NAP12.9 . HSA were removed faster than Ag1Ab1 complexes with NAP7.0 . HSA. The studied system adds covalently cross-linked immune complexes with multivalent antigens to the armamentarium of covalently cross-linked complexes that previously were obtained only with bivalent affinity labels.