ABSTRACT
Polysaccharides play an important role in the virulence of several encapsulated bacteria as they contain antiphagocytic properties in the absence of specific antibodies. Encapsulated bacteria like Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae, Salmonella typhi, Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae are common causes of diseases like pneumonia, meningitis, otitis media, septic shock, arthritis, typhoid fever, urinary tract infections and abscess formation. Vaccination with encapsulated bacteria resulted in many cases in the induction of anti-polysaccharide antibodies and, as was already demonstrated in the early twenties, antibodies against polysaccharides confer protection against bacterial infection. 1 A serious disadvantage of polysaccharides as vaccine components is their immunological classification as thymus independent type 2 (TI-2) immunogens. 2 , 3 This group of immunogens is characterized by induction of low avidity IgM abtibodies and the absence of immunological memory after immunization. The major handicap of these immunogens is, however, their inability to induce an immune respone early in the ontogeny. This is of great concern as, in particular, young individuals are affected by infections with encapsulated bacteria. 4 , 5
