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Fragmented CagA protein is highly immunoreactive in Japanese patients
Kazuki Yamada1, Toshiro Sugiyama, Hiroshi Mihara
1Department of Gastroenterology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
Helicobacter
|April 21, 2012
Summary
A new assay using Japanese strain-derived high-molecular-weight cell-associated proteins (JHM-CAP) improves accuracy for detecting H. pylori in East Asian populations. This is due to a unique 100-kDa CagA fragment that Japanese patients strongly react to.
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- The high-molecular-weight cell-associated proteins (HM-CAP) assay, widely used for serological immunoassay, shows reduced accuracy with sera from East Asian populations, including Japan.
- This reduced performance is attributed to differences in antigen composition between US and East Asian isolates.
Purpose of the Study:
- To develop and evaluate a modified enzyme immunoassay using Japanese strain-derived HM-CAP (JHM-CAP) to improve diagnostic accuracy in Japanese adults and children.
- To identify the specific antigen responsible for the enhanced performance of the JHM-CAP assay.
Main Methods:
- Immunoblot analysis and peptide mass fingerprinting were employed to identify the distinctive 100-kDa protein in JHM-CAP antigens.
- Mascot Search against the Helicobacter pylori database was used for peptide sequence identification.
- Confirmation was achieved through immunoblotting with specific antibodies and serum inhibition assays.
Main Results:
- A distinctive 100-kDa protein, identified as a fragment of CagA from Japanese isolates, was present in JHM-CAP but absent in US-derived HM-CAP.
- Fragmentation of CagA occurred during antigen preparation of Japanese isolates, a process not observed with US isolates under identical conditions.
- Sera from Japanese patients exhibited strong reactivity to this fragmented CagA protein, likely due to exposed epitopes.
Conclusions:
- The 100-kDa protein is a fragment of Helicobacter pylori CagA, specific to Japanese clinical isolates.
- Japanese patients, including children, demonstrate a strong immune response to exposed epitopes on this fragmented CagA, explaining the improved diagnostic accuracy of the JHM-CAP assay.
