BINDING TO PROTEIN A OF IMMUNOGLOBULIN-G AND OF FAB AND FC FRAGMENTS

Abstract

Protein A (pA) [from Staphylococcus aureus] may fix to the Fab region of Ig[immunoglobulin]G outside the antigen-binding site. pA-reactive Fab fragments were isolated from specific anti-egg albumin and specific anti-measles virus antibodies. A probable significance of this Fab reactivity in the precipitation reaction between IgG and pA is discussed. Reactive IgG from human, guinea pig, rabbit and porcine normal sera all showed similar avidity towards pA. Slight differences between IgG subclasses were observed. The avidity of pA-reactive Fab and Fc fragments isolated from normal porcine IgG was highest in the latter.