anti-Fc Antibody Research Articles

Relationship of Immunoglobulin to Complement Receptors of Human B Cells

Abstract By using the disappearance of the surface Ig from human peripheral lymphocytes as a parameter of modulation, at 37°C it was shown that anti-Fab antibody is a more effective and faster modulator of the surface Ig than anti-Fc, anti-IgM, or anti-IgG antibodies. The C-binding site was demonstrated to be fully independent and distinct from the surface Ig and a stable marker of Ig-bearing cells. The C receptor can be blocked by the addition of fresh C5-sufficient, C5-deficient mouse serum, or fresh autologous human serum, at 37°C before binding to EAC by a mechanism still to be defined. Both IgM and IgG cells possess the C receptor. The relationship of Ig to C receptors and their role in cell activation by the specific antigen is discussed.

Specificity of the Immunosuppression Caused by Passive Administration of Antibody

Abstract Antibody production against Fab and Fc determinants in rabbits immunized with varying doses of human immunoglobulin G (IgG) incorporated in incomplete Freund's adjuvant (ICFA) was determined using an antigen-binding capacity test. The kinetics of antibody formation and the amount of antibody produced against each group of determinants were usually comparable within the range of antigen doses used. Intravenous administration of rabbit hyperimmune anti-Fab or/and anti-Fc antibodies 1 hr before and 7 days after injection of rabbits with IgG in ICFA specifically inhibited antibody production to the corresponding determinants without affecting the immune response to the unrelated determinants inasmuch as kinetics of antibody formation, serum antibody levels and relative avidity of antibodies were concerned. The results suggest that passive antibody may inhibit the antigenic stimulus at the level of antigenic determinants rather than at the level of the whole antigenic molecule.

Studies on the Immunogenicity of Antigen-Antibody Precipitates

Summary Guinea pigs immunized with antibody excess immune precipitates of human γG globulin (HGG) and rabbit or guinea pig anti-Fab or anti-Fc antibody make little antibody to HGG. The small amount of anti-HGG antibody produced in each case was directed against antigenic determinants present in both the Fab and Fc portions of the HGG molecule, and thus bore no reflection on the specificity of the antibody in the complexes. This finding suggests that the suppression is to the whole antigen molecule rather than its individual antigenic determinants. The mechanism of the suppression of antibody formation to complexes comprised of immunogenic components cannot be explained in terms of antigenic competition for antibody-producing cells, nor in terms of “blocking” of antigenic determinants. It was shown that the combination of HGG with specific anti-Fab antibody at the equivalence point hinders only 21% of the Fc antigenic determinant, while in 4-fold antibody excess precipitates 66% of the Fc antigenic determinants are still capable of reacting with homologous antibody. Similarly, equivalence precipitates of HGG with anti-Fc antibody “block” only 16% of Fab determinants, whereas in 4-fold antibody excess precipitates 43% of the Fab determinants are “hidden.” Quantitatively, HGG bound in a 4-fold antibody excess precipitate with either anti-Fab or anti-Fc antibody has approximately 0.5% of the immunogenicity of the uncombined antigen. It thus appears that antigen in antibody excess immune precipitates is non-immunogenic, and that the antibody produced against HGG can be explained in terms of a 0.5% dissociation of the complex in vivo.