Low responsiveness to immunization with immunoglobulin E/antigen and immunoglobulin G/antigen complexes in H-2Ab mice

Immunoglobulin (Ig)E and IgG antibodies specific for 2,4, 6-trinitrophenyl (TNP) are able to enhance the carrier-specific antibody response to TNP-conjugated soluble proteins such as bovine serum albumin (BSA). We have recently reported that mice carrying the MHC class II Ab molecule are low responders to immunization with IgE/antigen complexes and now show that H-2Ab mice are also low responders to IgG/antigen complexes. In addition, we found that spleen cells from naive low- and high-responder mice captured IgE/antigen complexes exclusively on B cells, and that the binding was completely inhibited by monoclonal antibodies (MoAbs) against the low-affinity receptor for IgE (FcepsilonRII or CD23). The IgG/antigen complexes were targeted both to B cells and macrophages. The binding of IgG/antigen to B cells primarily seemed to be dependent on the low-affinity receptor for IgG (FcgammaRII or CD32), although some influence of complement receptor 2 (CR2 or CD21) was seen. Capture of IgG/antigen complexes on macrophages was partially blocked by MoAbs against FcgammaRII/III. There was no difference in expression of FcepsilonRII, FcgammaRII/III, CR1, CR2, and CR3 between low- and high-responder strains, thus excluding low levels of these FcRs and CRs as a reason for low responsiveness in H-2Ab mice.