Can DPC's I. D. Blot™
Help in Assessment of H. pylori Virulence?

At the 2000 General Meeting of the American Society for Microbiology in Los Angeles, Dr. A. Van der Ende et al. (Academic Medical Centre, Amsterdam) presented a study titled "Prevalence and relationship with disease of CagA-positive Helicobacter pylori in primary care patients." The study examined the presence of CagA-specific antibodies in different ethnicities with and without ulcer disease. Patient CagA status was tested with DPC's I. D. Blot™
H. pylori IgG* test (serum samples), along with a CagA PCR assay (cultured biopsy isolates). Preliminary findings suggest a utility for the I. D. Blot assay in assessing H. pylori virulence based on the patient antibody response.

H. pylori-associated disease
Not everyone infected with H. pylori will develop a peptic ulcer. It is not yet fully understood when ulcers develop, or why some individuals develop a duodenal ulcer and others a gastric ulcer. Differences in host, H. pylori strains, ethnicity and environmental factors could play a role.

It is known that H. pylori strains exhibit a significant degree of diversity. The
great variability in the H. pylori genome may explain why not all infected individuals suffer from ulcer. Some H. pylori strains contain particular pathogenic genes such as cytokine-associated gene A (CagA), while others lack these genes. The CagA protein of H. pylori has been found to be associated with more severe clinical manifestations, such as ulcer disease and gastric cancer. Thus, discrimination between potentially virulent strains may be relevant.

H. pylori infections are usually diagnosed by 1) culture of gastric specimens obtained by endoscopy; or 2) noninvasive methods such as serological testing for an antibody response, or radiolabeled urea-based breath tests. Serological tests—mostly immunoassays—have been widely used in epidemiological and diagnostic evaluations. These assays are rapid, easy to perform, and can be automated. Assay sensitivity and specificity are remarkably good.

Despite the availability of these assays, the management of H. pylori infections is still a matter of confusion, particularly among primary care physicians. Moreover, numerous countries lack national guidelines for this rapidly growing area of medicine.

Study findings
Figure 1 depicts the association between CagA-positive status and ulcer disease in a population of primary care patients in Amsterdam. These patients were categorized according to place of birth. Group A patients were born in The Netherlands; group B patients were born elsewhere. Group A exhibited a significant association between CagA-positive status and ulcer disease: a much higher percentage of patients with ulcers were CagA positive than were patients without ulcers. In group B patients, however, no significant association between CagA status and ulcer disease emerged, because nearly identical percentages of patients with and without ulcer disease were CagA positive.

Figure 1. Association between disease and CagA-positive status in H. pylori-infected patients.

The study also found that the prevalence of CagA-positive H. pylori was higher among patients born outside The Netherlands (group B) than among patients born in The Netherlands (group A).

Figure 2 shows the CagA-positive status by CagA PCR assay performed on culture biopsy isolates from patients who were positive by DPC's I. D. Blot
H. pylori IgG test. The CagA PCR assay appeared to be less sensitive than the blot assay for assessing patient CagA status. A possible explanation is the heterogeneous distribution of a mixed population of CagA-positive and CagA-negative H. pylori in the stomachs of the patients. A biopsy taken from a lesion harboring a CagA-negative H. pylori strain would yield a CagA-negative result by PCR. The use of a specific serology immunoblot allows detection of the antibody response against all H. pylori strains.

Figure 2. PCR results for 121 primary care patients with CagA-positive I. D. Blot results.

Conclusion
This study demonstrates that the DPC I. D. Blot H. pylori IgG test is a very useful and simple tool for identifying differences in virulence factors between H. pylori strains. I. D. Blot can also be used as an additional indicator of antibody response when the outcome of an EIA is doubtful. The use of a serological test to identify specific antibodies to CagA or other separate proteins could reduce the need for endoscopy and could be enormously useful in decisions regarding treatment. The study also demonstrates, however, that results may vary among different population groups. This fact should be considered when testing in other geographic areas.

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