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Updated: Mar 16, 2026
Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Published on: February 24, 2014
Structural validation and immunogenic characterization of Streptococcus pneumoniae serotype 22A capsular
Xiongyan Meng1, Huimin Yang1, Yannan Xue1
1School of Pharmaceutical Sciences, Key Laboratory of Tropical Biological Resources of Ministry of Education, Hainan University, Haikou 570228, China.
Abstract:
Streptococcus pneumoniae serotype 22A is a significant contributor to invasive pneumococcal disease (IPD) in selected regions and is closely related to the vaccine-included serotype 22F. The repeating unit (RU) structure of serotype 22A capsular polysaccharide (CPS) was reported in a patent. In this study, we performed a comprehensive structural validation combining chemical derivatization, high-resolution MS, and NMR spectroscopy to confirm the RU structure, O-acetylation pattern, as well as its immunological characterization relative to 22F. The RU of 22A CPS was confirmed as: [→3)-β-D-Galf-(1 → 2)-α-L-Rhap-(1 → 4)-β-D-GlcAp-(1 → 4)-(α-D-Galp-(1 → 3))-β-L-Rhap-(2-OAc)(1 → 4)-β-D-Glcp-(1→]n. It is highly similar to that of 22F, with the key difference being a side chain α-d-galactopyranose in 22A versus α-d-glucopyranose in 22F. O-acetylation was also identified as an important structural feature. Immunogenicity was assessed using 22A and 22F CPS-CRM197 conjugates in rabbits. Both vaccines elicited robust antibody responses. Glycan microarray analysis revealed cross-reactive binding between 22A and 22F, while also demonstrating that O-acetyl group is a key contributing factor for antibody recognition. These findings provide the detailed structural characterization of 22A CPS, establish its distinction from 22F, and highlight the roles of side chain sugar and O-acetylation in immunogenicity, offering guidance for pneumococcal vaccine design.
Insights
Streptococcus pneumoniae serotype 22A structural characterization reveals key differences from serotype 22F, particularly a side chain sugar and O-acetylation. These features are crucial for understanding pneumococcal disease and designing effective vaccines.
Area of Science:
- Microbiology
- Immunology
- Structural Biology
Background:
- Streptococcus pneumoniae serotype 22A causes invasive pneumococcal disease (IPD) and is structurally similar to vaccine antigen 22F.
- Previous reports on the repeating unit (RU) structure of 22A capsular polysaccharide (CPS) were limited.
Purpose of the Study:
- To comprehensively validate the RU structure of 22A CPS.
- To elucidate the O-acetylation pattern and compare immunogenicity with 22F CPS.
- To guide the development of novel pneumococcal vaccines.
Main Methods:
- Chemical derivatization
- High-resolution mass spectrometry (MS)
- Nuclear Magnetic Resonance (NMR) spectroscopy
- Immunogenicity assessment in rabbits
- Glycan microarray analysis
Main Results:
- The RU structure of 22A CPS was confirmed, differing from 22F CPS by a side chain α-d-galactopyranose instead of α-d-glucopyranose.
- O-acetylation was identified as a significant structural feature of 22A CPS.
- Both 22A and 22F CPS-CRM197 conjugates induced robust antibody responses in rabbits, with cross-reactivity observed.
- The O-acetyl group was found to be critical for antibody recognition.
Conclusions:
- Detailed structural characterization of 22A CPS distinguishes it from 22F.
- Side chain sugar and O-acetylation play vital roles in the immunogenicity of pneumococcal serotypes.
- Findings provide essential data for designing next-generation pneumococcal vaccines.
