Biochemical and Immunological Insights into Capsular Polysaccharide of Streptococcus pneumoniae Serotype 38 (American

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M V N Janardhan Reddy1, Yogeshwar Devarakonda1, Rajendar Burki2

  • 1Department of Biological Sciences, Birla Institute of Technology and Science, Pilani, Hyderabad Campus, Jawahar Nagar, Kapra Mandal, Medchal District, Telangana 500078, India.

ACS Omega
|September 2, 2025
PubMed

Insights

Characterizing nonvaccine pneumococcal serotype 38 polysaccharide reveals unique biochemical and immunological properties. These findings are crucial for developing new vaccines and therapeutics against invasive pneumococcal disease.

Area of Science:

  • Microbiology
  • Immunology
  • Biochemistry

Background:

  • Invasive pneumococcal disease remains a significant global health threat, particularly for vulnerable populations like children and the elderly.
  • Existing vaccines (PPSV23, VAXNEUVANCE, PREVNAR 20) do not cover all serotypes, and nonvaccine serotypes are increasingly implicated in disease and mortality.
  • Characterizing emerging nonvaccine serotypes is critical for advancing pneumococcal disease prevention strategies.

Purpose of the Study:

  • To comprehensively characterize the biochemical and immunological properties of the capsular polysaccharide from prevalent nonvaccine serotype 38 (American type 71).
  • To identify critical quality attributes of serotype 38 polysaccharide that may influence its behavior and potential as a vaccine target.
  • To investigate potential cross-reactivity with other serotypes based on structural and immunological similarities.

Main Methods:

  • Employed advanced analytical techniques including multiangle light scattering (MALS), ion chromatography, and dynamic light scattering.
  • Utilized conventional biochemical methods and SLOTBLOT analysis for detailed characterization.
  • Assessed immunological properties through cross-reactivity studies with existing polyclonal sera.

Main Results:

  • Serotype 38 polysaccharide exhibits a molar mass of 768 kDa and a z-average radius of gyration (Rg) of 90 nm.
  • Composition analysis revealed galactose, N-acetylglucosamine, galacturonic acid, and the amino acid serine; near-zero zeta potential suggests a zwitterionic or uncharged nature.
  • Demonstrated immunological cross-reactivity with serotype 5 and serotype 1 sera, attributed to shared epitopes and similar net charge properties.

Conclusions:

  • Novel biochemical and immunological characteristics of serotype 38 polysaccharide, including amino acid content and charge, have been identified.
  • These unique properties provide valuable insights into the behavior of nonvaccine serotypes.
  • Findings may inform the development of novel therapeutics and more effective vaccines against invasive pneumococcal disease.

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