Helicobacter pylori vs immune system or antibiotics

Abstract

Helicobacter pylori (H. pylori) infection has often no clinical signs and is one of the most common bacterial infections. All infected subjects have histology of active chronic gastritis. In some cases patients develop peptic ulcer and minority of them develop gastric cancer. Gastric cancer is multifactorial disease, thus various progressions of H. pylori infection and disease are dependent on the host genetic factors, the characteristics of the individual’s immune response, environmental factors, and different bacterial virulence factors of the individual bacterial strains. Eradication of the bacteria plays a crucial role in the treatment of these cases however antibiotic therapy does not always help. Bacteria often develop resistance to antibiotics so we recommend that not only screening for H. pylori also the strain determination should have some diagnostic value, especially in the patients who already developed gastritis. Furthermore, for such patients assessment of disease progression (atrophic or metaplastic gastritis) could be followed by polymorphism determination. Until now we cannot predict the disease based only on single polymorphism. Bacteria successfully neutralize the responses of the immune systems using different enzymes or even components of the host immune response. However, the influence of immune system and its components could represent new ways of treatments and could help to eradicate the infection.

Key Words: Helicobacter pylori; Resistance to antibiotics; Immune response; Genetic factors; Bacterial eradication

Core tip: Combination of Helicobacter pylori (H. pylori) and host-associated risk factors do not always allow evaluation of gastric carcinoma. We have learnt that the assessment of patients with H. pylori infection and its strain is very important and concluded that eradication of bacteria has essential meaning. We recommend that not only screening for H. pylori also the strain determination should have some diagnostic value, especially in the patients who already developed gastritis. Furthermore, for such patients assessment of disease progression could be followed by polymorphism determination. Conclusions indicate that host cytokine genotypes, host immune response, as well as H. pylori strains could be important for greater risk for developing gastric cancer.

INTRODUCTION

Helicobacter pylori (H. pylori) is 3-5 μm Gram-negative microaerophilic bacterium. It colonizes the gastric mucosa and metaplastic gastric epithelium of duodenum. It has characteristic spiral morphology with more flagella at one pole and is capable of moving in the protective gastric mucus layer. It has enzymes catalase, oxidase and degrades urea. While living in extremely unfavorable environment of low pH in the stomach, the protection for survival is provided by the clearance of gastric mucus and secretion of proteases that degrade additional mucus, and urease that produces ammonia, which helps to raise the pH in the vicinity of bacteria[1,2].

Epidemiology

H. pylori infection results in chronic active gastritis, and 20% of infected also develop ulcers of the stomach or duodenum. In some cases infection leads to stomach cancer and MALT lymphoma. Although H. pylori is not invasive bacteria, the mechanisms of mucosal inflammation and tissue damage and the onset of the disease are a combination of bacterial and host factors[2]. H. pylori is a human pathogen, and its reservoir is the human stomach. It colonizes cardio, corpus and antrum of the stomach. The transmission of H. pylori from the stomach of one human to another is not yet fully clear. The transfer is most common within families and during childhood. In all likelihood, there are two routes of transmission; the oral-oral route and the fecal-oral route. Fecal-oral route is associated with the ability of bacteria to survive outside its primary environment. For this pathway certain conditions must be met, namely the rapid passage through the intestine, most often in the case of diarrhea, inadequate sanitation and sewage disorder. Furthermore, contamination of drinking water by sewage is also possible. Such conditions are usually found in developing countries where the prevalence of H. pylori infection is greater than in developed countries. Oral-oral route is associated with regurgitation of gastric juice and thus passage of bacteria in the mouth and the transmission of H. pylori in close contact to another person[3,4]. H. pylori infect more than half of the world’s population. This bacterium can be left in the gastric mucosa for a long time, without causing disease symptoms including rare spontaneous disappearance from the stomach[3]. The highest infection rate is 54% of the age group 60 to 69 years. In the age group 0-19 years, 10% of those living are infected, and in the age group between 20 and 49 years 29% of the population is infected with H. pylori[5].

The pathogenesis and virulence factors

H. pylori has adapted to live between the protective layer of mucus and epithelial cells of the gastric mucosa. The bacterium develops in neutral pH, and is changed to coccoid shape at a pH below 4 or above 8. The gastric mucosa can be damaged directly or indirectly by influencing on the homeostasis of acid secretion[6].

The inner part of the H. pylori cell membrane, which is situated at the cytoplasmic membrane, consists of peptidoglycan. On the outer side the outside membrane with anchored lipoproteins is located, which are sometimes covalently bound to the peptidoglycan. The main surface components of Gram-negative bacteria are lipopolysaccharides (LPS), which protect the bacteria from the environment[3]. The basis represents the lipid A of LPS, which allows the biological activity of the endotoxin[3,7]. H. pylori has enzyme urease on the outer and inner membrane, which can be excreted in the neighborhood through the membranes of dead cells. It degrades urea to ammonia and bicarbonate, and thus neutralizes the acid environment. The bacterium is able to attach on epithelial cells of the gastric mucosa and moves as a spiral through the mucus in the stomach. The enzymes protease, lipase and phospholipase allow to cleavage the glycoprotein of mucous gel into a more hydrophobic structure, which can cause diffusion of hydrogen ions and possible damage to the mucosa. Ammonia can react with hypochlorous acid of neutrophils resulting in cytotoxic compounds such as monochloramine and hydroxylamine[7].

Genetic information for vacuolization cytotoxin (Vac A) have all H. pylori, approximately 50% of them produce 67 kDa protein, which causes the formation of vacuoles in epithelial cells of the gastric mucosa. Cytotoxin-associated gene A (Cag A) is the genetic makeup of the 127 kDa protein, which is present in all strains. Bacteria that produce CagA cause pronounced secretion of IL-8 from epithelial cells, resulting in increased mobilization of neutrophils and a higher level of active chronic gastritis. Neutrophils cannot effectively phagocyte bacteria and at quicker rupture of the neutrophils free oxygen radicals are released, which further failures the mucous membrane. Patients infected with Cag A-positive strains have increased risk for the development of duodenal ulcers and gastric cancer[6,8].

H. pylori has a protein which causes the attachment of neutrophils to the endothelial cell lining of the stomach and is called HP-NAP (H. pylori neutrophil-activating protein). Different degrees of attachment of neutrophils were observed, which are caused by different activities of this protein in various strains of H. pylori, which indicates different levels of expression of this protein as similar to protein Vac A. HP-NAP is located in the cytosol of bacteria and is released during lysis. It binds to the outer surface of the outer membrane, similar as urease. The majority of patients infected with H. pylori produce a specific antibody to HP-NAP. Vaccination of mice with the protein HP-NAP provided protection against infection with H. pylori. Protein plays an important role in the immune response to infection with the bacterium. HP-NAP is chemotactic for monocytes and neutrophils, and causes increased expression of β2-integrins on neutrophils and monocytes. HP-NAP works through activation of NADPH oxidase in neutrophils and thereby induces the production of reactive oxygen intermediates Reactive oxygen intermediates. HP-NAP represents a virulence factor that is associated with the pathogenic effects of the H. pylori to the site of infection[9].

H. pylori affect the homeostasis of gastric acid secretion through changes in paracrine hormone control system for gastrin and acid secretion. Normally, the release of gastrin leads to acid secretion and lowering the pH below 3 promoting cells D to somatostatin secretion, which in paracrine route inhibits the release of gastrin, and consequently acid secretion. Proteins and fatty food in the duodenum via cholecystokinin stimulate the secretion of somatostatin and thereby inhibit further secretion of acid. Patients with duodenal ulcer and infected with H. pylori, have increased sensitivity of the parietal cells to gastrin. These patients, when stimulated with food or with gastrin, secrete larger amounts of stomach acid than healthy people. After removal of bacteria, secretion of gastrin normalizes, the amount of acid is reduced by 50%, and completely normalizes only after one year. Infected patients have also reduced secretion of bicarbonate into the duodenum. After removal of the bacteria this is also normalized[6].

Virulence factors CagA and VacA and the development of gastric cancer

Virulence factors CagA and VacA are the most important factors of H. pylori in the development of the disease. The CAG-pathogenetic islands (cagPAI) have the information for the type IV secretory system, which is required for peptidoglycan to enter the cell. CagA phosphorylates cellular proteins, which are known oncogenes[10]. The motive for the phosphorylation of CagA is located within the amino acid motif EPIYA. A larger number of EPIYA-C within CagA damage more cells and more severe course of the disease occurs, especially gastric cancer[11]. CagA after phosphorylation connects to the proteins in the cell, which causes an increase in signal similar to that in the expression of growth factors in the cell. It affects the proliferation and adhesion of cells and the organization of the cytoskeleton[12].

VacA is a protein that forms pores in the cell and causes vacuolization and cell death. It is involved in the presentation of antigen and causes efflux of ions out of the cell due to the impact on the integrity of close connections between cells (tight junction). It is also a potent inhibitor of cell activation of T-lymphocytes in vitro[13,14]. H. pylori has several versions of the protein VacA. Type VacA s1/m1 is the most cytotoxic. Interesting findings are that CagA positive strains has vast majority of s1 type VacA. Vac A has two versions, i1 and i2. Protein VacA s1/m1 i1 is often present in patients with gastric cancer[15].

The immune response to infection

Chronic gastritis is associated with increased local production of IgG, increased infiltration of the mucous membrane with T cells, and increased expression of HLA class II molecules[16,17]. In addition, chronic gastritis is a H. pylori infection associated with other diseases, such as acute gastritis, peptic ulcer on duodenum, lymphoma of gastric mucosa and gastric adenocarcinoma, which is divided into intestinal and less common diffuse type[18]. The development of disease stages can be divided into three entities. Simple gastritis caused by infection with bacteria, acid secretion is normal. Duodenal ulcer occurs when infection with the bacterium occurs, antral gastritis is present, and acid secretion is increased. This type of patient is protected from gastric cancer. H. pylori chronic gastritis in patients with gastric cancer is more intense in the corpus, also more extensive intestinal metaplasia and atrophy of the mucosa are present. There is not enough acid, so intestinal metaplasia might develop, which leads to the intestinal-type of gastric cancer[19,20].

Infection with H. pylori causes an increased concentration of IL-8, IL-1, IL-6 and TNF-α. IL-8 in tissue, which activates neutrophils, results in the epithelial cells, as well as in other cells in the wall of the stomach. Expression is dependent on the adherence and the genotype of the cagA. The immune response Th1 is triggered in case of infection by intracellular pathogens and cancer, immune responses Th2 is characterized in infection by extracellular pathogens. In contrast to the expected reaction in the host with H. pylori infection, Th1 immune response is particular. Bacteria should choose an immune response by stimulating IL-12, which leads to a Th1 response. Thus stimulated immune system cannot overcome the infection. The cellular immune response and the formation of IgG antibodies which can activate complement cause intense inflammation and further damage to the mucosa. Neutrophils which are attracted and activated by IL-8 are an important component in the development of chronic active gastritis. The result of infection with the same strain of H. pylori could be different in the immune response of the different entities[6,21].

Infection of the gastric mucosa, accompanied by a strong neutrophilic infiltration of the mucosa, significantly contributes to the formation of gastritis. Strains of H. pylori, which are capable to activate neutrophils, are more common in patients with peptic ulcer than in patients with chronic active gastritis[9].

H. pylori possess number of factors that contribute to the colonization and to bacterial adherence. BabA binds to antigens of Lewis b blood group, which are on the cells of the epithelium, and can contribute to the adhesion of bacteria. Transgenic mice expressing more Lewis b blood group have had heavier chronic gastritis and have lost several parietal cells[4]. SabA is a protein on the outer membrane of H. pylori and binds to a glycoprotein antigen of Lewis x blood group and facilitates adhesion. Similar role has OipA. OipA is on the membrane of H. pylori is more pronounced in people who already have precancerous changes. Bacteria survive easier in the epithelial cells, since it is difficult to mechanically removed[22].

The influence of immune system on the success of treatment of H. pylori infection

In addition to H. pylori for the development of the disease we must also consider the immune system. T lymphocytes in the gastric mucosa mostly express IFN-γ, which indicates Th1 immune response[23]. In patients who have weakened immune response despite treatment with antibiotics are not healed. T lymphocytes without additional stimulation with antigens of H. pylori produce smaller amounts of IL-4 than in patients whose therapy was successful with antibiotics[24]. In the patients who received antibiotic therapy and are cured, T lymphocytes, stimulated by antigens of H. pylori, express larger amounts of IFN-γ molecules compared to the patients who do not recover despite receiving treatment against bacteria. In cured patients compared with those which were not cured, an increased expression of IFN-γ and IL-4 was observed, when T-lymphocytes were stimulated with dendritic cells, which have been in contact with H. pylori antigen[25].

One of the possible methods for treatment of H. pylori infection could be in vivo addition of recombinant IFN-γ. In normal humans, the addition of IFN-γ mimics the physiological response to bacterial infection, causing increased expression of FcγRI, which is proportional to the biological activity of IFN-γ on neutrophils and monocytes, which enhances phagocytosis by neutrophils mediated by FcγR. In addition to improved defense in normal humans, recombinant IFN-γ also helps in treating various disorders of immunity[26].

It was also found that IL-12 produced by the antigen-presenting cells (APC), in the H. pylori infection effected naive CD4-T-lymphocytes, which are directed towards a Th1 response through the transcription factor T-bet and STAT4. This suggests that the infection with H. pylori is an important stimulus for the secretion of IL-12[27].

Moreover, IL-18 affects the production of IFN-γ released by T-lymphocytes and NK cells. If the mucosa is infected with H. pylori, the regulation of IL-18 expression is influenced by CagA and OipA. Epithelial cells produce IL-18 under the influence of two virulence factors, while monocytes produce more IL-18 only under the influence of OipA. These data confirm the importance of IL-18 in the development of gastritis due to H. pylori infection[28]. Th17 T cells could also play an important role in infection with H. pylori. It is anticipated that IL-17 plays an important role in mucosal immunity. The expression of IL-17 in the case of H. pylori infection is affected by IL-23. If this path is blocked, the infected mucosa has less IL-17[29,30].

APCs have on their membranes’ receptors that recognize PRR (Pattern Recognition Receptors), which include Toll-like receptors (TLR). These are specific receptors, which are involved in the mechanisms of innate immunity and can trigger a series of defense mechanisms, such as complement activation, phagocytosis and expression of genes associated with inflammation. TLR receptors recognize conserved structure of microorganism, which are relatively stable within certain groups of microbes and are called Pathogen-Associated Molecular Pattern or PAMP[31]. TLRs recognize different molecular components of microorganisms. Examples of ligands are LPS from the cell wall of Gram-negative bacteria, peptidoglycan, lipoproteins and lipopeptide from the cell wall of Gram-positive bacteria. TLRs detect some bacterial proteins such as flagellin, and a foreign nucleic acid. LPS was the first detected ligand for the TLR, which is recognized by TLR-4. TLR-4 is part of the lipopolysaccharide receptor CD14, and for recognition binding of the complex of LPS and LPS binding protein (LBP) to the receptor CD14 is required[32,33].

On the surface of the membrane of Gram-negative bacteria are LPS, which protect bacteria against bile salts, hydrophobic antibiotics and complement activation. LPS after release organize in aggregates. Using protein LBP a complex LPS-LBP is formed. This binds to the membrane protein CD14 (mCD14), which is located on monocytes, or a soluble CD14 protein (sCD14) which is present free in the serum[31]. LPS of H. pylori (Hp LPS) is, compared to the other Gram-negative bacteria, poor immunogen. In addition, Hp LPS as compared to other bacteria binds poorly to the TLR-4 on epithelial cells. TLR-2 and TLR-5 are more important for the innate immune response of epithelial cells on H. pylori[34,35]. Due to the poor immunogenicity of Hp LPS scientists began to look for other receptors, which participated in the initial process of the immune response. They found that an important role play H. pylori peptidoglycans, which are an important link in the development of mucosal immunity. Peptidoglycan enters the epithelial cell using the type IV secretory system, which genetic information is located in cagPAI of H. pylori. Inside the cell it binds to the NOD-like receptor, which ultimately increases the kinase activity of NF-κB, which activates cell proliferation, and then through the other signals the activation of the immune system[35].

Dendritic cells (DC) play an important role in directing the immune response. H. pylori is presented to other immune cells, especially T lymphocytes, and is involved in their activation. In what way DC focus the immune response is not yet fully understood. We know that the response of DC depends on the virulence factors of H. pylori and the host immune competence[16]. DC can direct differentiation of T lymphocytes into Th1 subsets, with the consequent emergence of severe gastritis, or subsets Th2, which causes lighter inflammation. Th2 response, in the case of H. pylori infection, is less frequent than Th1. The differentiation in regulatory T-lymphocytes is also possible, which limits the immune response and thereby prevents the formation of more severe forms of inflammation, what helps H. pylori to survive[17,36]. DCs which present antigens of H. pylori, strongly activate T-lymphocytes, influence on the production of cytokines and initiate an inflammatory process. H. pylori LPS (Hp LPS) stimulate DC via TLR[37]. TLR are less important for the immune response in the case of epithelial cells, however the APC use TLR for the immune response[38]. DC, together with the cytokines and costimulatory molecules, affect other inflammatory cells, especially the T lymphocytes. Measurement of the immune response in case of infection with H. pylori could help to assume in which patients standard therapy with antibiotics are more likely to be ineffective[25].

The influence of host factors on the development of gastric cancer

Several host genetic factors are important for the progression and development of gastric cancer. Single nucleotide polymorphisms or point mutations in genes for cytokines affect gastric acid secretion and innate immune response[39-42]. Polymorphisms in genes may influence the level of the cytokine production, and consequently influence the disease outcome[43].

IL-1β is mainly secreted in response to H. pylori infection. It has a proinflammatory activity and strongly inhibits gastric acid secretion[44]. Inhibition of acid secretion leads to the spread of bacteria from the antrum to the corpus, and consequently the development of corpus predominant gastritis which further leads to the development of gastric cancer[45,46]. Three polymorphisms were described in the IL-1B gene at positions -31, -511 and +3954 from the transcription start site[45,47]. IL-1B-31*C and IL-1B-511*T alleles are associated with hypochlohydria or decreased acidity in the stomach in response to the H. pylori infection[45]. IL-1β receptor antagonist polymorphism (IL-1ra) has also been associated with the level of IL-1β secretion. Genotype IL-1RN*2 is associated with higher secretion of IL-1β, most probably through the reduction of its receptor antagonist IL-1ra[47,48].

TNF-α as a central mediator of the immune response has several polymorphisms in the promoter region of TNF-A gene of which -308*G > A was associated with increased production of TNF-α in response to the infection, and increased risk of gastric cancer[49-51]. El-Omar et al[52] and Machado et al[53] found that patients with this polymorphism have almost two-fold increased risk of gastric cancer.

At the position +896, in exon 4 of the TLR-4 gene a functional polymorphism has been described. This A > G transition results in an alteration of the extracellular domain of TLR-4, that causes hyporesponsiveness to LPS, reduced epithelial TLR-4 density and exaggerated inflammatory cytokine response[54]. A recent studies have reported an association of TLR-4 gene polymorphisms with gastroduodenal diseases such as gastric atrophy, hypochlorhydria and noncardia gastric cancer[55-58].

Furthermore, our results on Slovenian population showed that males were more predominant to develop gastric cancer than females. Meanwhile females had 2-fold greater probability to develop chronic gastritis[59]. We also proved that IL-1B-511*C homozygote allele was most frequent in chronic gastritis group (58.8%). Such results were not found in any other study. According to our findings, individuals carrying the IL-1B-511*T/T allele, both homozygotes and heterozygotes, compared to control group showed an increased OR for gastric cancer. Moreover, no indications that the infection with H. pylori in a given inflammatory genotype could result in an inflammatory response, and then gastritis or cancer could be found[59]. TLR-4 or TNF-A polymorphism did not play a role in the development of gastric premalignancies. The results were comparable to those by Garza-Gonzales et al[55] and confirmed in review by Figueiredo et al[60] for TLR-4. Meanwhile, in 2015 Trejo-de la et al[61] suggested that 2848G > A polymorphism in TLR-9 increased the risk for the development of duodenal ulcer.

Treatment of H. pylori infection

In addition to the immune response, which is difficult to influence, an appropriate antibiotic therapy is important. Infection with H. pylori is most effectively cured with a proton pump inhibitor (PPI) and a combination of two antibiotics. We mainly use metronidazole and clarithromycin or clarithromycin and amoxicillin or amoxicillin and metronidazole. Certain strains of H. pylori became resistant to metronidazole and clarithromycin. However, with antibiotics we cannot eradicate H. pylori in about 10% of patients in whom the bacterium is not resistant to selected antibiotics[62-64]. If we want to successfully treat the H. pylori infection, we need to know the primary resistance of H. pylori to antibiotics. Less developed regions have a very high resistance to clarithromycin and metronidazole, in the case of metronidazole ranging up to 100%[64]. Indications for treatment and methods of treatment are set out in national and international guidelines. The success of the treatment decreases with age, and the 7-d treatment in the United States is between 57% and 73%. The reasons for the decline in the performance of treatment are mainly the creation of resistance of H. pylori to antibiotics and poor patient compliance with the treatment[65-67]. In Slovenia the performance of traditional 7-d treatment regimen OMC (proton pump inhibitor such as PPIs, omeprazole 2 × standard dose, metronidazole 2 × 400 mg, clarithromycin 2 × 250 mg) and OAC (PPIs, 2 × standard dose amoxicillin, 2 × 1000 mg, clarithromycin 2 × 500 mg) was last checked 10 years ago. In 1997 and 1998, the effectiveness of treatment with the scheme OMC was 82.6% and in the group treated with the scheme OAC 82%[68-70].

Globally the decline in the success of the treatment of H. pylori infection with a regimen that last 7 d was detected. The success of treatment is between 57% and 73%. In Europe the resistance to clarithromycin is in the range between 1% and 21.3%, metronidazole between 14.4% and 38%. In Slovenia in 2000 H. pylori was resistance to clarithromycin 3.7%, and to metronidazole 18.5%[71,72]. It was determined that there is still adequate resistance to clarithromycin between 15 and 20%. When a certain area exceeds this limit, it is necessary to think about replacing clarithromycin with another drug or control the sensitivity of each H. pylori isolate and adjust therapy to antibiogram. In 2010 in our group of Slovenian isolates we found 18.6% resistance to metronidazole and 17.5% resistance to clarithromycin. We have found that combined resistance to metronidazole and clarithromycin is 4.1%. Resistance to amoxicillin and tetracycline were not detected. Resistance to ciprofloxacin is 3.1%[73].

It is not always the fault of bacterial resistance to antibiotics for failed eradication. As mentioned above, in about 10% we fail to eradicate bacteria in the stomach, despite adequate sensitivity[72-74], and although patients followed doctor’s instructions about taking antibiotics after repeated therapy failed to remove bacteria. With a better understanding of the mechanism of the immune response during infection and treatment we could explain why some patients despite antibiotic therapy do not react appropriately and the problems due to repeated infections persist and do not lead to eradication of bacteria[64,74].

Cathepsins

For this type of protease has long been thought that their application is restricted to the final degradation of proteins in lysosomes, but it was subsequently proved to be involved in several very important cellular processes. It is considered that cathepsins are involved in intra- and extracellular protein decomposition, processing pro-peptides and hormones, apoptosis, transformation of bone tissue, reproductive processes and the processes of differentiation, in addition, increased motility and invasion in the cells. Cysteine cathepsins are involved in various effector mechanisms of acquired and innate immune response and are essential for an effective immune response. Cathepsins are also indispensable for differentiation, adhesion and migration of immune cells, regulation of cytokines, induction of apoptosis, and many other processes[75]. Disturbed regulation of their enzymatic activity is associated with cancer, and their manipulation is shown as an option for the development of new drugs[76,77]. Cathepsins are important targets for the development of new molecules for the diagnosis, prognosis and therapy of cancer[78,79].

The activity of cathepsins is controlled by regulating the synthesis and processing of cathepsins, inhibition of endogenous inhibitors (stefins and cystatins) and pH stability[80]. Conventional cathepsins are lysosomal enzymes which are only active at acidic pH. This has changed the fact that many cathepsins in physiological and pathological conditions diverted from lysosomes into the extracellular space in other cellular organelles or in the cytoplasm and can be active at neutral pH[81].

Cathepsin X and the immune response to infection with H. pylori

Cathepsin X is a lysosomal cysteine protease located in macrophages gathered from gastric mucosa. Patients with H. pylori gastritis had a higher concentration of cathepsin X protein and cathepsin X mRNA levels in gastric mucosa compared to H. pylori negative patients[82]. Cathepsin X was also up-regulated in the gastric mucosa of patients with gastric cancer in contrast to patients without cancer[83].

We tested if the inhibition of cathepsin X influences the successful immune response to a H. pylori infection. We have proved the involvement of cathepsin X in the antigen presentation with TLRs. When THP-1 cells with different strains of H. pylori were stimulated, the addition of the inhibitor of cathepsin X resulted in a higher expression of TLR-4 on the membranes of THP-1 cells. This was especially true in clarithromycin sensitive strains of H. pylori. The expression of TLR-4 and TLR-2 was significantly higher when H. pylori stimulated DCs were cultivated together with cathepsin X inhibitor compared to the dendritic cells stimulated with H. pylori only[84].

The influence of higher expression of TLR-4 on the membranes of THP-1 cells on the production of cytokines IL-1b, IL-8, IL-10, and IL-6 was also tested. The concentrations were lower in the group of H. pylori strains that were resistant to clarithromycin. The same was seen in the THP-1 cells where we added bacteria along with the inhibitor of cathepsin X. It seems that the inhibition of cathepsin X influences the concentrations of cytokines, as well on the TLRs, that are crucial for efficient regulation of immune response to H. pylori. We discovered that strains that are resistant to clarithromycin are less immunogenic than clarithromycin sensitive strains and that they are capable of surviving an immune system attack for a prolonged period of time and as well develop resistance to clarithromycin that further attributes to eradication failure of H. pylori[84].

We have proved that resistance to clarithromycin can be a problem for the eradication since such strains seem to be less immunogenic. We assumed that the inhibition of cathepsin X to control the immune response in the cases with impossible eradication of H. pylori would not be beneficial. The immune response to infection would be delayed and thus could lead to persistence of bacteria and possible disease progression from atrophy, metaplasia to gastric cancer. On the other hand, when gastric cancer is already developed, inhibition of cathepsin X could be helpful since we could influence the process of cell senescence and also influence tumour cell growth.

CONCLUSION

After this review we can conclude that H. pylori are very successful bacteria avoiding host immune response to infection. Furthermore, not only infection itself, but also the immune response is important for the development of gastric cancer. Host cytokine gene polymorphisms represent just one component of complex interactions among host, pathogen, and environmental factors involved in gastric carcinogenesis. Only combination of H. pylori and host-associated risk factors do not always allow evaluation of gastric carcinoma. The disease progression from infection through atrophy to neoplastic transformation depends on other factors, including diet and different pathogenesis of H. pylori strains. Now we have learnt that the assessment of patients with H. pylori infection and its strain is very important and concluded that eradication of bacteria has essential meaning. We recommend that not only screening for H. pylori also the strain determination should have some diagnostic value, especially in the patients who already developed gastritis. Furthermore, for such patients assessment of disease progression (atrophic or metaplastic gastritis) could be followed by polymorphism determination. Altogether, conclusions indicate that host cytokine genotypes, host immune response to infection, as well as H. pylori strains could be important for greater risk for developing gastric cancer. However, we think those parameters alone could not predict the incidence and risk of the disease, only the combination could be of greater value.