Structural and Antigenic Relationships Between Avian Immunoglobulins

Abstract

Hydrolysis with papain of chicken IgG (C-IgG), pheasant IgG (P-IgG) and quail IgG (Q-IgG) produced fragments with sedimentation coefficients of 3.5S. Approximately 40% to 50% of the IgG was converted to dialyzable peptides. Digestion of C-IgG pseudoglobulin preparations with 1% pepsin at pH 4.5 for 18 hr, in the absence of a reducing agent, produced Fab′ (3.4S) fragments. Digestion of C-IgG with pepsin at pH 5.0 produced a small amount of 5.4S fragments, Fab′ and undigested IgG. Chicken pseudoglobulin and euglobulin IgG appeared to have different susceptibilities to digestion with pepsin. Digestion of P-IgG with 1% pepsin, at pH 4.5, resulted in 5.4S fragments and undigested IgG, whereas digestion with 2% pepsin yielded mainly 5.4S and a small amount of Fab′. The F(ab')₂ fragment contained no Fc determinants, but compared to papain-produced Fab it had additional antigenic determinants. Digestion of Q-IgG with 1% pepsin, pH 4.5, produced about 60% Fab′ and 40% 5.4S fragments. With respect to the kinds of fragments formed, Q-IgG was intermediate between C-IgG and P-IgG. Large amounts of dialyzable peptides were formed from the three immunoglobulins by peptic digestion.