Isolation and characterization of structurally homogeneous antibodies from antipneumococcal sera.

Antibodies of sufficient homogeneity for sequence studies were readily obtained in high concentrations from rabbits immunized with pneumococcal vaccines. By taking advantage of slightly differing immunologic specificity for Type III and Type VIII capsular polysaccharides, an antibody with unique electrophoretic mobility could be isolated from serum containing several distinct antibody components by using appropriate cross-reacting immunoadsorbents. A unique sequence for the N-terminal 11 amino acid residues of the light chain of the antibody was found, in contrast to several sequences in the antibody mixture from which this component was isolated. The sequence of a nonimmune light chain pool demonstrates even greater heterogeneity. Chymotryptic peptide maps of the antibody light chain show two unique cysteine-containing variable region peptides not seen in maps of nonimmune light chain pool of the same allotypic specificity as that of the antibody light chain. The experimental approach described here may provide further insight into the structure-function relationship of several homogeneous antibodies of closely related specificity for the same polysaccharide antigen.