Immunogens capsular polysaccharides

Clearly, further studies will be necessary to sort out the multiple factors involved in the in vivo immune response to C. neoformans carbohydrate-mimetic peptides. Several conclusions may be drawn from the results to date. Peptides that mimic the cryptococcal capsular polysaccharide show specificity, in that each peptide binds with differing affinity to closely related mAbs [140,149]. The pattern of binding to protective and nonprotective mAbs differs between the mimetic peptides and the polysaccharide [140]. Protective efficacy is related to the location of carbohydrate epitopes recognized by these mAbs, within the polysaccharide capsule, but hkely also depends on interactions between mAbs and cellular responses [149]. Peptides have been shown to be functional, immunogenic mimics, but their protective efficacy depends on multiple factors, including the type of Abs elicited and interactions with the cellular immune system. Protective efficacy does not correlate with binding affinity to representative mAbs, but rather depends on the nature of these interactions. 

A similar situation exists with the K5 antigen. Figure 15 shows that this capsular polysaccharide is practically identical with a precursor of heparin. It was in fact shown recently that the K5 polysaccharide is a substrate for the de-N-acetylase which initiates the processing of this precursor to heparin. Structural relatedness may not be the only cause for the very low immunogenicity of a coli capsular antigen, but it appears quite suggestive. 

Campbell, W.N., Hendrix, E., Cryz, S.J., Cross, A.S. Immunogenicity of a 24-valent Klebsiella capsular polysaccharide vaccine and an 8-valent Pseudomnas O-polysaccharide conjugate vaccine administered to acute trauma victims, Clin Infect Dis 23 (1996) 179-181. 

Kanra, G. Yurdakok, K. Ceyhan, M. Ozmert, E. Turkay, F. Pehlivan, T. Immunogenicity and safety of haemophilus influenzae type B capsular polysaccharide tetanus conjugate vaccine (PRP-T) presented in a dualchamber syringe with DTP. Acta Paediatr. Jpn. 1997, 39, 676-680. 

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