Identification of a genetic marker of Helicobacter pylori strains involved in gastric extranodal marginal zone B cell lymphoma of the MALT-type

Abstract

Background and aims: Gastric extranodal marginal zone B cell lymphoma of the mucosa associated lymphoid tissue (MALT)-type (MZBL) is a rare complication of Helicobacter pylori infection. Currently, no bacterial factor has been associated with the development of this disease. Our aim was to identify genes associated with lymphoma development.

Methods: We used subtractive hybridisation as a tool for comparative genomics between H pylori strains isolated from a patient with gastric MZBL and from a patient with gastritis only.

Results: When gastric MZBL strains were compared with gastritis strains, two open reading frames (ORFs) were significantly associated with gastric MZBL: JHP950 (74.4% v 48.7%, respectively; p = 0.023) and JHP1462 (25.6% v 2.6%, respectively; p = 0.004). The prevalence of JHP950 was 48.8% (p = 0.024) in duodenal ulcer strains and 39.3% (p = 0.006) in gastric adenocarcinoma strains, which makes this ORF a specific marker for gastric MZBL strains. In contrast, the prevalence of JHP1462 was 16% (p = 0.545) and 35.7% (p = 0.429) in duodenal ulcer and adenocarcinoma strains, respectively. These ORFs were present in reference strain J99 but not in reference strain 26695. JHP950 is located in the plasticity zone whereas the other, JHP1462, is located outside. Both encode for H pylori putative proteins with unknown functions.

Conclusion: Despite its low prevalence, the ORF JHP1462 can be considered a candidate marker for H pylori strains involved in severe gastroduodenal diseases. In contrast, the ORF JHP950 has a high prevalence, and is the first candidate marker for strains giving rise to an increased risk of gastric MZBL strains. Further confirmation in other studies is needed.

Figure 1

Expression of the open reading frames (ORFs) JHP950 and JHP1462 of Helicobacter pylori determined by reverse transcription-polymerase chain reaction (RT-PCR) in the “tester” strain. Lanes M1 and M2 correspond to ΦX174 DNA/HaeIII markers (Eurobio) and to the 1 kb DNA ladder (Promega), respectively. Lanes 1, 4, and 7 correspond to PCR control on genomic DNA. Lanes 2, 5, and 8 correspond to RT-PCR product obtained on RNA extracted from the “tester” strain. Lanes 3, 6, and 9 correspond to PCR results on RNA preparations without the RT amplification step. Lanes 1–3, 4–6, and 7–9 correspond to templates amplified for JHP950, JHP1462, and vacA genes, respectively.

Figure 2

Distribution of the combination of iceA1 allele, sabA functional status, and the open reading frame (ORF) JHP950 according to Helicobacter pylori strains isolated from patients with gastric extranodal marginal zone B cell lymphoma of the MALT-type (gastric MZBL) or gastritis alone.