To the Editor:
In 2007, the European Respiratory Journal published a letter by Ibrahim [1] in which it was suggested that micro-aspiration of Helicobacter pylori from gastric juice secondary to gastro-oesophageal reflux disease (GORD) may cause or contribute to the development of idiopathic pulmonary fibrosis (IPF) through recurrent lung insult. This hypothesis was derived from the observation that GORD is common in IPF patients [2, 3], while in the general population the prevalence of GORD exceeds that of IPF. Ibrahim [1] postulated that only a small proportion of subjects with GORD develop IPF, probably those with H. pylori in their gastric juice. This theory has not yet been investigated and no data is available in the literature on the relationship between H. pylori infection and IPF.
H. pylori is a Gram-negative, spiral bacterium. There are two major groups of H. pylori microorganisms: type I, which expresses the vacuolating cytotoxin VacA and the cytotoxin-associated gene CagA and is responsible for mucosal damage, inducing local inflammatory response; and type II, which expresses neither of these proteins and does not determine any injury [4]. Type I strains, which have the chromosomal insertion called Cag, are endowed with increased inflammatory function that may determine further augmentation of local and systemic cytokines [5].
H. pylori infection is very common all over the world and does not seem to have sex or racial prevalence. CagA H. pylori strains play a role in gastroduodenal ulcers and the development of gastric cancer. H. pylori infection was recently demonstrated to protect against gastro-oesophageal reflux disease and reflux esophagitis [6], to be associated with several extragastric disorders [7] and to play a role in respiratory disorders, such as chronic bronchitis and lung cancer [4, 8, 9]. A protective function in bronchial asthma, rhinitis and T-helper cell type 2 (Th-2) driven disorders in general has been proposed [10].
In order to contribute to the analysis of H. pylori infection in IPF, we designed a pilot study that included serological analysis. We evaluated serum-prevalence of total anti-H. pylori antibodies (anti-HP Ab) and anti-CagA antibodies (anti-CagA Ab) in a population of IPF patients. 45 patients with IPF (33 males, mean age 66.2±10.2 years, 12 out of 45 had a histologically confirmed diagnosis and 33 out of 45 had a definite high-resolution computed tomography (HRCT) diagnosis) monitored at the Regional Referral Center for Sarcoidosis and other Interstitial Lung Diseases at Siena University (Siena, Italy), were enrolled, consecutively, in the study. Inclusion criteria were: 1) a documented history of IPF of >1 year; 2) diagnosis of IPF performed according to American Thoracic Society/European Respiratory Society/Japanese Respiratory Society/Asociación Latinoamericana del Tórax guidelines [11]; 3) regular follow-up with chest HRCT (almost one a year); 4) pulmonary function tests (PFTs) performed according to guidelines (almost every 6 months). Patients with malignancies and pulmonary hypertension were excluded.
The results were compared with a population-based sample of 797 age- and sex-matched controls with a comparable socioeconomic background (Siena Osteoporosis Cohort) [12], obtained from primary care registers of Siena residents.
All participants gave their written informed consent to the study that was approved by the local ethics committee.
Serum IgG antibodies to H. pylori were analysed in all patients and controls by ELISA having a sensitivity and specificity of 96% (Diesse Diagnostica Senese, Monteriggioni, Italy); serum anti-CagA IgG antibodies were determined by ELISA with a sensitivity of 95% and a specificity of 90% (CagA-IgG; Genesis Diagnostics Ltd., Cambridgeshire, UK). Cut-off values of 6.2 IU·mL−1 for anti-HP antibodies and 5.5 IU·mL−1 for anti-CagA antibodies were based on previous studies [5].
Statistical analysis was performed using GraphPad Prism version 4.0 for Macintosh, p <0.05 was considered significant. Differences between the two groups were studied by Mann–Whitney test; analysis of variance was done by Kruskal–Wallis test, while Fisher's exact test or the Chi-square test was applied to evaluate prevalence by contingency tables. All data was expressed as mean±sd.
table 1 reports the prevalence of anti-HP Ab and anti-CagA Ab in the IPF population together with demographic data, functional test parameters at baseline and at 1-year follow-up, bronchoalveolar lavage (BAL) cell pattern, CD8:CD4 ratio, and 6-month and 1-year mortality rates.
Serum IgG antibodies against H. pylori proved positive in 18 out of 45 patients with IPF (prevalence 40%), 10 of whom were also positive to anti-CagA serum antibodies (55%). The population-based control group showed a H. pylori infection prevalence of 51.4% (410 out of 797), 206 of whom were positive to anti-CagA serum antibodies (50.2%).
Prevalence of H. pylori infection was not significantly different in patients and the general population (OR 0.62, 95% CI 0.43–1.16; p = 0.16,), and the same was found for infection by CagA-positive H. pylori strains (OR 1.23, 95% CI 0.47–3.20; p = 0.81). No significant difference between antibody titres of anti-HP Ab (p = 0.06) and anti-CagA Ab (p = 0.06) was found.
IPF patients testing positive for H. pylori showed significantly lower values of forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1) and total lung capacity (TLC) than those testing negative for H. pylori (p = 0.016, p = 0.026, and p = 0.037, respectively) (table 1). No statistically significant difference was found for DLCO, although the number of patients unable to perform the test due to severe lung impairment and oxygen-therapy was higher in H. pylori-positive (44.4%) IPF patients than the H. pylori-negative IPF patients (25.9%), suggesting their worse respiratory condition, although the difference was at the limits of significance (p = 0.07).
6-month follow-ups recorded the death of 18 out of 45 IPF patients giving a mortality rate of 40%. There was a statistically significant difference in the mortality rate of the two subgroups: 11 (61.1%) out of 18 H. pylori-positive patients died versus 7 (28%) out of the 25 H. pylori-negative patients who died (two patients were lost to follow-up) (p = 0.05). 1-year mortality rate was higher in the H. pylori-positive group when compared with the H. pylori-negative group (66.6% versus 37%, respectively; p>0.05).
1-year follow-up PFTs were available in six H. pylori-positive patients (12 died) and 15 H. pylori-negative patients (10 died and two were lost to follow-up), showing a significant decrement in FVC in both groups (p<0.05). The decrement was significantly greater in H. pylori-positive patients when compared with the H. pylori-negative patients (-11% versus -5.3%, respectively; p<0.05). Follow-up of DLCO was available in only four H. pylori-positive patients and 12 H. pylori-negative patients and the decrease was not significant in either group (-12.6% versus -6%, respectively; p>0.05).
No statistical differences in therapy and in BAL features were found between H. pylori-positive and H. pylori-negative IPF patients (data not shown).
No differences were observed in the prevalence of H. pylori-CagA positivity between patients and controls and no correlations were found between total anti-HP Ab or anti-CagA Ab and the clinical variables analysed.
In this pilot study, the prevalence of H. pylori infection in IPF patients was comparable to that of the general population and H. pylori antibodies were associated with a more severe disease (i.e. H. pylori-positive IPF patients had significantly lower FEV1, FVC and TLC than H. pylori-negative patients). Interestingly, in the literature, GORD is reported to be highly prevalent in IPF patients and has been hypothesised as a potential cause of the disease [2, 3]. The role of H. pylori in the development of IPF has been postulated but never demonstrated [1].
In our study, the H. pylori-positive subgroup of IPF patients showed a more severe disease phenotype with higher rates of mortality and PFT decline, suggesting a possible role of this bacterium in disease progression. The theory put forward by Ibrahim [1] is interesting and our study suggests the potential role of H. pylori in IPF progression. At a recent International Conference (6th WASOG Conference, held in Paris, June 6–7, 2013), Hogaboam [13] reported positive H. pylori staining in lung biopsy specimens from severe IPF patients, sustaining the involvement of H. pylori in this disease. No other literature is available in this field of research.
The next step for our study will be direct determination, such as faecal H. pylori antigens or H. pylori determination in BAL (i.e. DNA PCR or culture), in a wide population of IPF patients. The effects of IPF pharmacological treatments on H. pylori infection remain to be established.
Footnotes
Conflict of interest: None declared.
- Received June 19, 2013.
- Accepted September 19, 2013.
- ©ERS 2014
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