Immunogenicity of FaB fragment of protein-315 for BALB/cmice.

Immunogenicity of Protein-315 and its Fab fragment (Fab-315) for isologous and heterologous strains of mice was investigated by comparing the characteristics of the anti-idiotypic response produced in BALB/c and A/J mice. The ability of these anti-idiotypic antisera to compete with DNP-lys for the ligand-binding site of Protein-315 were analyzed by comparing their hapten inhibition curves. The anti-idiotypic responses of BALB/c mice to Protein-315 and to Fab-315 were similar to one another with regard to antibody specificity and sensitivity to inhibition by hapten, suggesting that both forms were equally immunogenic in inbred BALB/c mice. This observation indicates that the Fc portion of Protein-315 is not essential for the induction of anti-idiotypic response. Both BALB/c and A/J mice recognized the same antigenic determinants on Fab-315 since the anti-idiotypic antibodies produced by these animals were indistinguishable with regard to their interaction with Protein-315, Fv-315, and sensitivity to hapten inhibition. On the other hand, the response of A/J mice to Protein-315 was remarkably different from that of BALB/c mice since it was found that Protein-315 seemed to be more immunogenic in A/J mice than in BALB/c mice. The data also indicated that Protein-315 was more immunogenic than Fab-315 in stimulating the anti-idiotypic response in A/J mice. A/J antiserum to Protein-315 was found to have antibodies specific for the ligand-binding site as well as those specific for other antigenic determinations on the Fc portion. These findings suggest that the Fc portion of Protein-315 may either act as a haptenic determinatant to provoke directly the antibody response or as a carrier determinant to enhance the anti-Fab response in A/J mice.