Passive cutaneous anaphylaxis with antibody fragments.

Pepsin-digested rabbit antibody (5S) provoked reverse passive cutaneous anaphylaxis in the guinea pig, but was somewhat less effective, mole for mole, than the native antibody. Fixation of guinea pig complement by the pepsin-digested antibody could not be demonstrated either in vitro or in vivo. Splitting of the 5S fragment into two monovalent fragments (3.5S) markedly reduced the capacity to provoke reverse passive cutaneous anaphylaxis.