Polysaccharide-iron-regulated cell surface protein conjugate vaccine: its role in protection against Klebsiella pneumoniae-induced lobar pneumonia.

Klebsiella pneumoniae has become an important cause of both community-acquired and nosocomial infections. In this study an attempt was made to study the immunogenicity of iron-regulated cell surface proteins (IRCSP) alone or in conjunction with the polysaccharide moiety of lipopolysaccharide (LPS) of K. pneumoniae. The polysaccharide-iron-regulated cell surface protein conjugate (PS-IRCSP) was non-toxic and non-pyrogenic. It was found to be immunogenic and the protection afforded by the conjugate against the challenge strain was observed in a rat lobar pneumonia model. The protection observed with the conjugate was higher than that observed with polysaccharide or IRCSP alone. The conjugate elicited both agglutinating and bactericidal antibodies. Enhanced phagocytosis was observed for the alveolar macrophages obtained from the lungs of animals treated with conjugate compared with macrophages obtained from animals treated with other antigenic preparations.