Role of the Fc Fragment in the Regulation of the Primary Immune Response

Abstract

SPECIFIC antibody, passively transferred, has the capacity to inhibit the production of the specific immune response (reviewed in ref. 1), and may even terminate a response². There have been several reports dealing with the ability of F(ab′)₂ antibody (the antibody fragment which has the two antigen-binding sites but lacks the Fc fragment) to suppress the primary immune response (refs. 3–5, and F. J. Dixon, quoted in ref. 1). The specificity of this type of immunosuppression is best explained in terms of antigen–antibody binding so that the antigenic site is masked, and so it was not surprising that F(ab′)₂ was found to induce antibody-mediated suppression of the immune response. In an initial attempt at preparing F(ab′)₂ antibody, however, we found that all the suppressive activity in the F(ab′)₂ preparation could be explained on the basis of contaminating whole 7S antibody. We report here the results of experiments in which the 5S F(ab′)₂ antibody digested by pepsin and remaining undigested 7S antibody were separated on sucrose gradients and their activities in suppressing the primary antibody response tested separately.