Protection against
pneumococcal disease is thought to be mediated primarily by
antibodies that are opsonic [Musher DM, Chapman AJ, Goree A, Jonsson S, Briles D, Baughn RE. Natural and
vaccine-related immunity to Streptococcus pneumoniae. J Infect Dis 1986;154(2):245-56]. Pneumococcal capsular
polysaccharide (CPS) is immunogenic and induces type-specific protective immunity. For convenience, the protective capacity of serum
antibodies is often evaluated by the measurement of antibody titers in an ELISA test. The pneumococcal capsular
polysaccharide (CPS) used in ELISA contains several impurities; these include about 5% by weight of teicholic
acid (CWPS) and the cholin
binding protein,
pneumococcal surface protein A (PspA) [Sorensen UB, Henrichsen J. C-
polysaccharide in a
pneumococcal vaccine. Acta Pathol Microbiol Immunol Scand C 1984;92(6):351-6; Yu J, Briles DE, Englund JA, Hollingshead SK, Glezen WP, Nahm MH. Immunogenic
protein contaminants in
pneumococcal vaccines. J Infect Dis 2003;187(6):1019-23]. All individuals have
antibodies to CWPS possible as a result of early exposure to pneumococci, Streptocuccus mitis and Streptocuccus oralis [Bergstrom N, Jansson PE, Kilian M, Skov Sorensen UB. Structures of two cell wall-associated
polysaccharides of a Streptococcus mitis biovar 1 strain. A unique teichoic
acid-like
polysaccharide and the group
O antigen which is a C-
polysaccharide in common with pneumococci. Eur J Biochem 2000;267(24):7147-57. [4]]. The concentration of the CWPS
antibodies in non-immunized individuals often exceeds the concentration of the serotype-specific pneumococcal
antibodies. Therefore, the pneumococcal ELISA requires an adsorption step to remove the unprotective CWPS
antibodies [Konradsen HB, Sorensen UB, Henrichsen J. A modified
enzyme-linked
immunosorbent assay for measuring type-specific anti-pneumococcal capsular
polysaccharide antibodies. J Immunol Meth 1993;164(1):13-20. [5]; Concepcion N, Frasch CE. Evaluation of previously assigned antibody concentrations in pneumococcal
polysaccharide reference serum 89SF by the method of cross-standardization. Clin Diagn Lab Immunol 1998;5(2):199-204. [6]; Kayhty H, Ahman H, Ronnberg PR, Tillikainen R, Eskola J. Pneumococcal
polysaccharide-meningococcal outer
membrane protein complex
conjugate vaccine is immunogenic in infants and children. J Infect Dis 1995;172(5):1273-8. [7]; Koskela M. Serum
antibodies to
pneumococcal C polysaccharide in children: response to acute pneumococcal
otitis media or to vaccination. Pediatr Infect Dis J 1987;6 (6):519-26. [8]]. Recently a new pneumococcal CPS ELISA was recommended with an extra serum absorption step with 22F CPS to remove
antibodies against an extra unknown common cross-reactive component. The aim of this study was to characterize the active component in the 22F
capsule. A non-capsulated pneumococci was prepared from a 22F capsulated pneumococci. The cell wall
polysaccharide (CWPS2) purified from this pneumococci has a better adsorption potential than 22F
capsule in the pneumococci ELISA. Structure characterization of the commercial available CWPS and CWPS2 was done by nuclear magnetic resonance (NMR). The NMR results showed that commercial CWPS had one phosporylcholine per
sugar repeat while the CWPS2 had two phosporylcholine per
sugar repeat explaining an immunological difference between the two variants of CWPS. In addition the LicD2 gene responsible for the attachment of the second cholin in the CWPS tetra
sugar repeat was inactive in the strain used for purifying the commercial CWPS but active in the strain expressing CWPS2.