Helicobacter pylori colonization of the human stomach is associated with chronic gastritis and an increased risk of peptic ulcer disease (PUD), gastric adenocarcinoma and gastric mucosa-associated lymphoid tissue lymphoma 123. While some H. pylori-infected individuals remain asymptomatic, others develop severe gastric disease. Strain-dependent factors may account for differences in clinical outcome, in particular factors that modulate interactions between H. pylori and human gastric cells, such as outer membrane proteins (OMP) 456. Recently, the OMP coding gene homB was associated with an increased risk of PUD in Portuguese children and young adults (age < 40 years) 7. Moreover, in vitro assays showed that HomB contributes to the proinflammatory characteristics of H. pylori and is involved in bacterial adherence, these two phenomena being more pronounced when homB is present in two copies in a given strain, compared to one copy only 7. The homB 90%-similar gene, designated homA, was found to be associated with non-ulcer dyspepsia (NUD) in that same population 7.

In this study, we investigated gastric disease association with homB and homA, as well as the H. pylori virulence factors cagA, vacA and babA, in a panel of H. pylori clinical strains isolated from patients from East Asian and Western countries, presenting different gastric diseases, namely NUD and PUD. The correlation between those bacterial factors was also evaluated.

The presence of homB and homA in the H. pylori clinical strains was determined by PCR. Table 1 summarizes the characteristics of the study population. PCR products, corresponding to either homA, homB or both genes were obtained for all the 415 strains tested. The presence of both genes in the same genome was detected in 43 strains (10.4%) (36 PUD strains and 7 NUD strains). These strains were excluded from the analysis related to clinical outcome. Thus, a total of 372 strains were included. They comprised 197 strains isolated from PUD patients (66.3% male; 50.3 ± 14.5 years) and 175 strains isolated from NUD patients (53.7% male; 51.1 ± 13.4 years).

Using a large panel of H. pylori strains (n = 372) isolated from patients from East Asian and Western countries, it was possible to confirm the association of homB with PUD and homA with NUD, previously observed with H. pylori strains (n = 84) isolated from Portuguese patients 7. Considering the distribution according to geographical region, homB was found to be significantly associated with PUD in strains from Western countries. However, when considering each country individually, only a tendency was observed probably due to the small number of strains tested in each case. The most common H. pylori strain circulating in the East Asia was extremely virulent, harboring homB, cagA, and babA genes and the vacA s1 genotype, regardless of the clinical outcome. Consequently no association with a specific disease was found, confirming the results from previous studies 89. Indeed, exposure to risk factors must be heterogeneous to find an association, and this is not the case in Asia. In addition, other environmental factors, e.g. diet, and possibly host genetic factors, may contribute to this evolution 10.

The previously reported significant association of homB with PUD in young adults (age < 40 years, 32 patients) 7 was confirmed in the present study with a higher number of patients (n = 90).

Polymorphism in copy number of H. pylori OMPs may contribute to increase the fitness of the strain and also its virulence 41112. Indeed, the homB two-copy genotype was associated with an increased rate of in vitro interleukin-8 secretion as well as an increased in vitro adherence 7. Furthermore, it was the genotype most frequently found in strains from young adults with PUD, while homA single-copy was the most frequent in NUD strains, in agreement with previous data 7. Globally, these data suggest that in some populations, the severity of H. pylori-associated disease in younger subjects may be closely related to the virulence of the strain, irrespective of the contribution of host and/or environmental factors which play a major role in adults. On the other hand, the present study demonstrates that there is a marked geographical specificity regarding homB/homA copy number, particularly evident between East Asian and Western strains, but also amongst Western countries, suggesting that copy number of the homB/homA OMP coding genes also plays a role in adaptation to the human host.

Several H. pylori genes encoding OMP display allelic variation, as is the case of babA, babB 13, hopQ 14 and hopZ 15. In all of these cases, a conserved profile of gene segmentation is observed, with a variable region which defines the existence of at least two highly conserved allelic variants. Regarding homB and homA, no information on allelic variation is available to date. Further sequence analysis of these coding regions using H. pylori strains with different geographical background would allow assessing the existence of allelic variation and to evaluate whether different alleles could be associated with a specific clinical outcome and/or reflect a dissimilar geographical origin.

The cagA-positive and vacA s1 genotypes were independently associated with PUD in Western strains, but not babA. Previous publications reported a significant association between the presence of babA and PUD in Western strains 1617, contrasting with the present result. This discrepancy may be explained by the very heterogeneous Western study group with regard to the geographical origin of the strains, and also because of a possible absence of PCR amplification due to diversity within babA 1718.

homB was found to co-exist with the most virulent genotypes, while homA was more frequently found in strains lacking these genotypes, in agreement with previous results 7. Thus, it is likely that the phenotype resulting from the expression of cagA, vacA s1 and homB genes confers a biological advantage to the strain, with the cumulative action of each factor contributing at the same time to the fitness of the strains in vivo and to a more pronounced pro-inflammatory response. Another hypothesis would be that homB is linked to PUD only because of its association with other virulence factors. However, its role in H. pylori-associated inflammation and in bacterial adherence supports the hypothesis that homB contributes to disease development 7.

Globally, these results suggest that homB and homA seem to be good candidates for the pool of H. pylori factors involved in the determination of clinical outcome.

(PUD): Peptic ulcer disease; (GU): gastric ulcer; (DU): duodenal ulcer; (NUD): non-ulcer dyspepsia; (OMP): outer membrane protein; (OR): odds ratio; (CI): confidence interval.

The authors declare that they have no competing interests.

MO carried out the experimental design of the study, statistical analysis and co-drafted the manuscript; RC, YY and DQ carried out bacterial cultures and PCR; FM co-drafted the manuscript; LM supervised the study and AM supervised the study and co-drafted the manuscript. All authors read and approved the final manuscript.