Human anti-F(ab')2 antibodies and pepsin agglutinators react with Fv determinants.

Affinity-purified human IgG anti-tetanus antibody was subjected to papain and then pepsin digestion, and residual fragments retaining antibody activity were re-isolated by adsorption and elution from Sepharose-tetanus toxoid columns. Both Fab' and Fv fragments isolated by gel filtration showed strong reactivity with anti-F(ab')2 antibodies. Failure of tetanus toxoid to completely block reactivity of anti-F(ab')2 antibody with anti-tetanus Fv fragments indicates that these antibodies react with framework antigens within variable antibody regions.