Enhancement of the antibody response to protein antigens by specific IgG under different experimental conditions.

Specific stimulation of the antibody response to protein antigens by IgG antibodies was studied in vivo. The response to TNP-coupled keyhole limpet haemocyanin (KLH-TNP) was enhanced by a TNP-specific IgG monoclonal antibody, 7B4, as measured both in ELISA (enzyme-linked immunosorbent assay) and by ELISPOT (enzyme-linked immunospot) method. Enhancement was seen when using both high and low doses of antigen and antibody. The antibody response to TNP-coupled bovine serum albumin (BSA-TNP), but not to TNP-coupled ovalbumin (OA-TNP), tetanus toxoid (TT-TNP) or diphtheria toxoid (DT-TNP), was also efficiently augmented by 7B4. Enhancement was seen when using both high and low coupling ratio of TNP to KLH. The fact that IgG-mediated enhancement is seen under many different experimental conditions suggests that it is a physiologically relevant phenomenon. In order to enhance the response to KLH-TNP and BSA-TNP, 7B4 had to be injected while antigen was circulating in blood. This supports that IgG-mediated stimulation acts by concentrating circulating antigen into lymphoid centres.