Purification, Specificity, and Hypervariable Region Sequence of Anti-Pneumococcal Polysaccharide Antibodies Elicited in a Single Rabbit

Four homogeneous antibodies to type VIII pneumococcal polysaccharide (S8) were isolated from the serum of a single rabbit (3322) by affinity chromatography on an S8 immunoadsorbent by utilizing gradient elution with cellobiose and NaCl. The binding properties of these antibodies were determined by a radioimmunoassay with 125I-bovine γ-globulin-S8. Cellobiose (a disaccharide unit of S8) was the immunodominant group of each of the four antibodies, but each antibody bound to this disaccharide with different relative affinities. The amino acid sequences (positions 0–40) of three of the four antibody light chains were each different both in framework and first hypervariable region sequences. The fourth antibody light chain has a blocked amino terminus. These findings indicate that antibodies elicited by a relatively simple antigen and examined at one time during the course of immunization in a single rabbit may exhibit common specificities for an oligosaccharide determinant, yet have different binding affinities for that determinant as well as different primary structures in the complementarity (hypervariable) regions and framework regions.