Biological activities associated with the Facb fragment of rabbit IgG

Abstract

Various types of rabbit IgG Fc sub-fragment have been examined for a capacity to fix to heterologous (guinea-pig) skin and to react with rheumatoid anti-IgG-globulins. Facb fragments proved, somewhat surprisingly, to be inactive in both systems; thus resembling pFc′ and tFc′ fragments (derived from the C-terminal end of the Fc region) and in contrast to the active parent Fc fragment. The effect of acid treating whole IgG in a similar way to that employed in preparing Facb fragments was investigated. This treatment per se was found to result in no appreciable loss in biological activity. The demonstration that fragments incorporating the C H 2 or C H 3 structural domains are both inactive suggests the necessity for strict conformational integrity in the expression of at least some biological activities associated with the Fc regions of IgG molecules.