Immunization of Rabbits with Type II Pneumococcal Polysaccharide. ∗

Abstract

Summary

1. Type II pneumococcal polysaccharide was found to be antigenic in rabbits. 2. Rabbits injected intradermally or intravenously with minute amounts of type II pneumococcal polysaccharide developed an active resistance to intradermal infection with type II pneumococcus. 3. The pooled serum of rabbits injected intradermally with the polysaccharide protected mice against 10,000 LD of pneumococcus type II, but not against pneumococcus type I. 4. The pooled serum of rabbits injected intravenously with the polysaccharide protected mice against almost 10,000 LD of pneumococcus type II. 5. It is suggested that previous failure to immunize rabbits with type-specific polysaccharides may be attributed to the use of excess polysaccharide resulting in “immunological paralysis.” 6. The evidence shows that the mouse-protective antibody is the specific antipolysaccharide which occurs in amounts too small to be detected by quantitative precipitin technics. 7. An attempt to demonstrate univalency of the type-specific mouse-protective antibody failed.