Özet:
It has been known for a long time that passively administered antibodies (Abs) or
immune complexes regulate the immune response to their specific antigen (Ag). IgG
may sometimes suppress the humoral immune response against soluble antigens. The
exact mechanism behind this phenomenon has not been understood yet and the
requirement for the Fc part is still a matter of controversy. The present study was
undertaken to clarify whether there is a true IgG-mediated Fc-dependent suppression
of the immune response. Antigen and monoclonal antibody (mAb) used in this study
were recombinant human interferon gamma (r-hIFN-g) and mouse monoclonal
antibodies specific for human IFN-g [anti-hIFN-g mAb (CAy-IFNg38)] respectively.
An intact IgG-free preparation of Fab plus various Fc fragments was prepared from
papain-digested CAy-IFNg38. Ag/IgG and Ag/Fab complexes were prepared at
various molar ratios. Keeping the Ag doses constant, mice were immunized either
with Ag, Ag/IgG or Ag/Fab complexes. Primary immunization and the boosting were
performed with the samples in complete and incomplete Freund’s adjuvants
respectively. Specific antibody levels were measured by an ELISA. Immunization
performed with Ag/Fab complexes even at a molar ratio of 1:1.36 did not result in
marked suppression of the response when compared to that of Ag only-immunization.In contrast, Ag/IgG complexes resulted in nearly 90% suppression of the antibody
response. Our observations suggest that Fc part of IgG molecule plays a crucial role in
suppression of the in vivo antibody response against the Ag when complexed with
intact IgG.
