In vitro suppression of immunoglobulin allotype synthesis by Fab and F(ab′) 2 fragments of anti-allotype antibody

Abstract

The F(ab′) 2 and Fab fragments were prepared from IgG containing antiallotype antibody (Ab) specific for the kappa light chains (i.e., anti-b4) and were tested for their ability to suppress b4 allotype production in vitro. Spleen cells from a b 4b 5 heterozygous rabbit were incubated for 24 hr with the F(ab′) 2 or Fab fragments and then washed and cultured for an additional 4 days. The tissue culture supernatant fluids were analyzed for the b4 and b5 allotypes by a radioimmunoassay. The results clearly indicated that both types of IgG fragments can suppress the production of the b4 allotype. Thus, neither the Fc fragment nor the bivalency of the intact Ab molecule is essential for suppressing activity. This makes it highly unlikely that the allotype suppression in vitro occurs as a result of cell death. When equivalent amounts of the IgG, F(ab′) 2, or Fab anti-b4 preparations, as determined by their antigen binding capacity, were compared for their relative efficiencies in the induction of b4 allotype suppression, the IgG and F(ab′) 2 were found to be equally efficient, while the Fab fragment was less efficient than the bivalent Ab preparations.