Studies on the Immunogenicity of Antigen-Antibody Precipitates

Guinea pigs immunized with dinitrophenylated human γG globulin (DNP-HGG) formed precipitating antibody which reacted with the immunizing protein, with DNP coupled to heterologous carriers, and, in many cases, with the carrier (HGG) molecule itself. Delayed hypersensitivity reactions were directed almost exclusively against the DNP-HGG complex. When animals were immunized with the same quantities of DNP-HGG bound in antibody excess immune precipitates to either anti-DNP or anti-carrier (anti-Fc) the humoral responses to both the DNP and the carrier determinants were markedly reduced. On the other hand such precipitates were effective in initiating cell-mediated responses; delayed hypersensitivity skin testing revealed that these animals were indistinguishable in this respect from animals sensitized with “free” DNP-HGG. Animals rendered unresponsive to either the carrier (HGG) or the hapten molecules, by intravenous administration of either HGG or dinitrophenylated bovine serum albumin, produced minimal responses to simultaneous administration of DNP-HGG in complete Freund's adjuvant. In these animals both delayed hypersensitivity reactions and circulating antibody formation were markedly reduced. The results suggest that the “processing” of antigen to initiate cell mediated and humoral responses proceeds, at a very early stage, along different pathways.