Antigenicity and protective effects of type 3 pneumococcal polysaccharide in rats

The response to type 3 pneumococcal polysaccharide vaccination, the protective effect of type 3 pneumococcal polysaccharide vaccination, and the ability of hemagglutinating antibody to type 3 pneumococcal polysaccharide to cross the blood-brain barrier were studied in rats. Hemagglutinating antibody response to vaccination with type 3 pneumococcal polysaccharide was found to be dependent on the dose and route of inoculation. Intraperitoneal vaccination with type 3 pneumococcal polysaccharide protected the rats from subsequent intraperitoneal challenge with type 3 Streptococcus pneumoniae but had no effect after intracisternal challenge with type 3 S. pneumoniae. In the presence or absence of sterile meningeal inflammation, hemagglutinating antibody could not be found in cerebrospinal fluid of animals vaccinated intraperitoneally with type 3 pneumococcal polysaccharide. These results suggest that type 3 pneumococcal polysaccharide is antigenic in rats and intraperitoneal vaccination with type 3 pneumococcal polysaccharide does not protect against experimental meningitis because antibodies do not cross the blood-brain barrier.