Abstract
Rabbits were selected for their ability to produce structurally restricted anti‐polysaccharide antibodies when immunized with either type III or type VIII pneumococcal vaccines. Close relatives and offspring of these animals also exhibited this trait, indicating that it is inheritable. Within two groups of such restricted responders the trait could be observed with either type of vaccine. No correlation was observed with the magnitude of the immune response and the degree of antibody restriction. Furthermore, there was no correlation of this trait with sex, nor was there any obligate association with any a or b locus allotype. Isoelectric spectra of antibodies produced by individual rabbits showed no gross similarities, although siblings did appear to share components. In several instances, prolonged immunization of nonrestricted responders in these groups resulted in the production of structurally restricted antibodies. However, this was not a general phenomenon. Finally, some rabbits immunized with type III Pneumococcus produced restricted components that did not appear to possess anti‐polysaccharide activity.