Studies on the fate of different 125I-DNP-HSA conjugates in mouse peritoneal cells, spleen and liver in vivo, and mouse peritoneal cells in vitro

Drug-protein conjugates--VIII. The metabolic fate of the dinitrophenyl hapten conjugated to albumin

Dinitrofluorobenzene has been used as a model chemically reactive metabolite to investigate factors which determine the fate of drug-protein conjugates formed in vivo. The disposition of homologous and heterologous albumin conjugated with 3H-dinitrophenyl groups (3H-DNP) has been investigated in the male Wistar rat. After intravenous administration, conjugates were cleared from plasma, predominantly through the liver, and the hapten was excreted into bile and urine as the novel amino acid derivative N2-acetyl-N6-DNP-lysine. It is assumed that the product arises from lysosomal hydrolysis of the conjugate, followed by N-acetylation, since its biliary excretion was significantly reduced in animals pretreated with suramin, an inhibitor of lysosomal proteolysis. The clearance of DNP-albumin conjugates was dependent upon the degree of conjugation; conjugates with an epitope density of greater than 20 had a short (ca. 1 hr) half-life. In a second study, the disposition of DNP-autologous protein conjugates was monitored in the rabbit over 21 days. The plasma concentration-time profile of the serum conjugates indicated that clearance was dependent upon non-immune mechanisms and that intravenous administration of DNP-serum protein conjugates did not elicit an anti-DNP response.

Immunoglobulin A-mediated hepatobiliary transport constitutes a natural pathway for disposing of bacterial antigens

The possibility that hepatobiliary transport of immunoglobulin A (IgA) immune complexes might eliminate bacterial antigens was investigated in mice with pneumococcal type III capsular polysaccharide and C carbohydrate and corresponding monoclonal antibodies. Although all isotypes of antibody caused uptake by the liver, only IgA, but not IgG or IgM, antibodies transported these substances into bile where they were detected in the form of immune complexes and as free antigens. Small doses (10 micrograms or less) of passively administered IgA antibody were sufficient to induce measurable transport of capsular polysaccharide into bile. Transport of C carbohydrate was significantly correlated with the level of naturally occurring IgA antibodies specific for the phosphocholine determinant, but not with IgM or IgG antibodies. These results suggest that the continual process of hepatic uptake of circulating polymeric IgA may function to eliminate bacterial macromolecular products that are not readily susceptible to other mechanisms of disposal.

Clearance and glomerular localization of preformed DNP anti-DNP immune complexes

The in vivo behaviour of well-defined immune complexes in rats was studied using complexes derived from DNP-conjugated bovine thyroglobulin (DNP-BTG) and purified specific goat anti-DNP IgG. Both clearance and glomerular localization were mainly dependent on the nature of the antigen. Soluble immune complexes formed with DNP17-BTG were cleared faster and showed a more marked localization in the glomerular mesangium than complexes formed with DNP3.4-BTG. A slight increase in the antibody to antigen ratio seemed to facilitate mesangial localization of soluble immune complexes. Insoluble immune complexes showed temporary localization as microemboli in the lumina of glomerular and peritubular capillaries. This study thus shows that not only the size and composition of the complexes but also the nature of the antigen within the complex can influence the clearance and organ localization of circulating immune complexes.