Immune complex-mediated enhancement of antibody responses without induction of delayed-type hypersensitivity

Immunoglobulin (Ig)G and IgE antibodies enhance the humoral response in viv o to soluble antigens with which they form complexes. In vitro, antigen is targeted to B cells by IgE antibodies and to macrophages and dendritic cell s (DCs) by IgG, thus leading to increased antigen presentation to specific T cells. Possibly these mechanisms are also responsible for antibody-mediat ed enhancement in vivo. We now address the question of whether IgG- and/or IgE-antigen complexes can prime for delayed-type hypersensitivity (DTH), a reaction known to require primed T helper (Th)1 cells. Mice were immunized with IgG-anti-2,4,6-trinitrophenyl (TNP)/BSA-TNP or IgE-anti-TNP/BSA-TNP. M ice given BSA-TNP alone or BSA-TNP in complete Freund's adjuvans (CFA) were used as controls. DTH and IgG-anti-BSA levels were measured after subseque nt challenge with BSA. A potent BSA-specific antibody response was induced by IgE- or IgG-complexed antigen as well as by CFA/antigen but DTH-reaction s were only observed in mice immunized with CFA/antigen. Both IgE and IgG e nhanced the production of BSA-specific IgG1, IgG2a and IgG2b, although the most pronounced enhancement was seen in the production of IgG1. These findi ngs suggest that Th2 cells rather than Th1 cells are involved in the immune response to IgG- and IgE-immune complexes.