The influence of epitope density on the immunological properties of hapten-protein conjugates. II. The in vivo and in vitro metabolism of heavily and lightly conjugated protein.

In earlier experiments we showed that lightly hapten-coupled bovine serum albumin (e.g. DNP—BSA) elicited mainly IgG anti-DNP antibodies and concomitant immunological memory in mice, whereas DNP—BSA induced a primary IgM response, little IgG antibody and poor memory. Although the latter are characteristic of T cell-independent antibody responses, antibody formation to DNP—BSA was found to be highly thymus-dependent. In the present study the metabolism of DNP—BSA and DNP—BSA was investigated. DNP—BSA was rapidly cleared from the bloodstream, but persisted at much higher levels in the liver and spleen than DNP—BSA. DNP—BSA was taken up more efficiently by macrophage cultures than DNP—BSA, but released comparatively slowly. Analysis of culture supernatants showed that macrophages degrade both antigens to the same degree. We conclude that heavy dinitrophenylation decreases the susceptibility of DNP—BSA to degradation by lysosomal proteases, but the relationship between the metabolic behaviour of various DNP—BSA conjugates and their immunogenic properties is at present unclear.