Putative consequences of exposure to Helicobacter pylori infection in patients with coronary heart disease in terms of humoral immune response and inflammation

INTRODUCTION

Pathogens, including Helicobacter pylori (Hp), have been suggested to contribute to the development of coronary heart disease (CHD), although the evidence still remains insufficient. The study was focused on the exposure of CHD patients to Hp and resulting anti-Hp heat shock protein B HspB antibody production in relation to the level of serum lipopolysaccharide binding protein (LBP) as a marker of inflammation.

MATERIAL AND METHODS

One hundred seventy CHD patients and 58 non-CHD individuals participated in this study. Coronary angiography confirmed the atheromatic background of CHD. The panel of classical risk factors included: arterial hypertension, diabetes, total cholesterol, low-density lipoprotein (LDL)/high-density lipoprotein (HDL) cholesterol, triglycerides, obesity and nicotinism. The Hp status was estimated by (13)C urea breath test and serology. Immunoblot and ELISA were used for screening the sera samples for anti-Hp HspB immunoglobulins (Igs) and LBP.

RESULTS

Coronary heart disease patients were exposed to Hp more frequently than non-CHD individuals. This was associated with increased levels of specific anti-Hp IgG2 and IgA as well as total IgA. Hp infected CHD and non-CHD donors produced anti-Hp HspB IgG cross-reacting with human Hsp 60. In CHD patients the LBP level was significantly higher in comparison to non-CHD donors. This was related to the severity of the disease. Type I Hp strains stimulated higher LBP levels than less pathogenic type II isolates.

CONCLUSIONS

Lipopolysaccharide binding protein secreted in excess together with anti-Hp HspB, cross-reacting with human Hsp60, may increase the risk of vascular pathologies in Hp-exposed CHD patients.

Structural modifications of Helicobacter pylori lipopolysaccharide: An idea for how to live in peace

In this review, we discuss the findings and concepts underlying the “persistence mechanisms” of Helicobacter pylori (H. pylori), a spiral-shaped, Gram-negative rod bacterium that was discovered as a gastric pathogen by Marshall and Warren in 1984. H. pylori colonizes the gastric mucosa of nearly half of the human population. Infections appear in early childhood and, if not treated, persist for life. The presence or absence of symptoms and their severity depend on multiple bacterial components, host susceptibility and environmental factors, which allow H. pylori to switch between pathogenicity and commensalism. Many studies have shown that H. pylori components may facilitate the colonization process and the immune response of the host during the course of H. pylori infection. These H. pylori-driven interactions might result from positive or negative modulation. Among the negative immunomodulators, a prominent position is occupied by a vacuolating toxin A (VacA) and cytotoxin-associated gene A (CagA) protein. However, in light of the recent studies that are presented in this review, it is necessary to enrich this panel with H. pylori lipopolysaccharide (LPS). Together with CagA and VacA, LPS suppresses the elimination of H. pylori bacteria from the gastric mucosa by interfering with the activity of innate and adaptive immune cells, diminishing the inflammatory response, and affecting the adaptive T lymphocyte response, thus facilitating the development of chronic infections. The complex strategy of H. pylori bacteria for survival in the gastric mucosa of the host involves both structural modifications of LPS lipid A to diminish its endotoxic properties and the expression and variation of Lewis determinants, arranged in O-specific chains of H. pylori LPS. By mimicking host components, this phenomenon leaves these bacteria “invisible” to immune cells. Together, these mechanisms allow H. pylori to survive and live for many years within their hosts.

Antigen-specific lymphocyte proliferation as a marker of immune response in guinea pigs with sustained Helicobacter pylori infection

Helicobacter pylori (H. pylori) bacteria are human pathogens causing symptomatic gastritis, peptic ulcer or gastric cancer. Little is known about the kinetics of immune responses in H. pylori infected patients because the initial moment of infection has not been identified. Various animal models are used to investigate the immune processes related to H. pylori infection. In this study we checked whether H. pylori infection in guinea pigs, mimicking natural H. pylori infection in humans, resulted in the development of specific immune responses to H. pylori antigens by measuring the proliferation of lymphocytes localized in mesenteric lymph nodes, spleen and peripheral blood. The maturity of macrophages and cytokines, delivered by monocyte-macrophage lineage or lymphocytes, were considered as mediators, which might influence the lymphocyte blastogenic response. The obtained results showed the activation of T cells localized in mesenteric lymph nodes by H. pylori antigens in H. pylori infected guinea pigs four weeks postinfection. The blastogenic activity of lymphocytes was shaped by their interaction with antigen presenting cells, which were present in the cell cultures during the whole culture period. Moreover, the balance between cytokines derived from adherent leukocytes including interleukin 8--IL-8 as well as interferon gamma--IFN-γ, and transforming growth factor beta--TGF-β delivered by lymphocytes, was probably important for the successful proliferation of lymphocytes. The H. pylori specific lymphocytes were not propagated in peripheral blood and spleen of H. pylori infected animals. The modulation of immunocompetent cells by H. pylori antigens or their different distribution cannot be excluded.

Antigen-specific lymphocyte proliferation as a marker of immune response in guinea pigs with sustained Helicobacter pylori infection

Helicobacter pylori (H. pylori) bacteria are human pathogens causing symptomatic gastritis, peptic ulcer or gastric cancer. Little is known about the kinetics of immune responses in H. pylori infected patients because the initial moment of infection has not been identified. Various animal models are used to investigate the immune processes related to H. pylori infection. In this study we checked whether H. pylori infection in guinea pigs, mimicking natural H. pylori infection in humans, resulted in the development of specific immune responses to H. pylori antigens by measuring the proliferation of lymphocytes localized in mesenteric lymph nodes, spleen and peripheral blood. The maturity of macrophages and cytokines, delivered by monocyte-macrophage lineage or lymphocytes, were considered as mediators, which might influence the lymphocyte blastogenic response. The obtained results showed the activation of T cells localized in mesenteric lymph nodes by H. pylori antigens in H. pylori infected guinea pigs four weeks postinfection. The blastogenic activity of lymphocytes was shaped by their interaction with antigen presenting cells, which were present in the cell cultures during the whole culture period. Moreover, the balance between cytokines derived from adherent leukocytes including interleukin 8--IL-8 as well as interferon gamma--IFN-γ, and transforming growth factor beta--TGF-β delivered by lymphocytes, was probably important for the successful proliferation of lymphocytes. The H. pylori specific lymphocytes were not propagated in peripheral blood and spleen of H. pylori infected animals. The modulation of immunocompetent cells by H. pylori antigens or their different distribution cannot be excluded.

[Animal models for the study of Helicobacter pylori infection]

The Gram-negative bacillus Helicobacter pylori is widely recognized as a major etiologic agent responsible for chronic active gastritis, peptic ulcers, the development of gastric cancer and mucosa-associated lymphoid tissue (MALT lymphoma). Still, little is known about the natural history of H. pylori infection, since patients usually after many years of not suffering from symptoms of the infection are simply asymptomatic. Since the research investigators carried out on human models has many limitations, there is an urgent need for the development of an animal model optimal and suitable for the monitoring of H. pylori infections. This review summarizes the recent findings on the suitability of animal models used in H. pylori research. Several animal models are useful for the assessment of pathological, microbiological and immunological consequences of infection, which makes it possible to monitor the natural history of H. pylori infection. Preclinical investigations on animal models are an essential stage of research which enrich the knowledge on treatment and prevention strategies.

Helicobacter pylori-driven modulation of NK cell expansion, intracellular cytokine expression and cytotoxic activity

During Helicobacter pylori (Hp) infections, innate immune cells may be positively or negatively modulated by Hp compounds or by Hp-induced cytokines. We have shown previously that the natural cytotoxic activity of PBMC was lower in Hp-infected [Hp(+)] than Hp-uninfected individuals [Hp(-)]. Here, we asked whether the Hp-modulated cytotoxic amplitude is associated with changes in the number of NK cells, their activation or intracellular cytokine expression. Flow cytometry immunophenotyping of PBMC was performed with regard to the surface receptors CD3, CD56 and CD25, and intracellular cytokine expression of IL-2, IFN-γ and IL-10 after in vitro stimulation with Hp glycine acid extract (GE), Hp LPS or standard Escherichia coli LPS. Hp GE-driven enhancement of lymphocyte cytotoxic activity was associated with the expansion of CD3(-)CD56(+)CD25(+) NK cells and the up-regulation of IFN-γ and/or IL-2 synthesis, up to the higher level in Hp(-) than in Hp(+), while Hp LPS-mediated decrease in lymphocyte cytotoxicity was accompanied by the lack of CD3(-)CD56(+)CD25(+) NK propagation, the inhibition of pro-inflammatory cytokine expression and intense expansion of IL-10-producing NK cells. Thus, the cytotoxic and cytokine activities of NK cells were dependent on the type of antigenic challenge and the Hp status, that is, NK cells could be modulated positively by Hp GE Ags and negatively by Hp LPS.

Helicobacter pylori-driven modulation of NK cell expansion, intracellular cytokine expression and cytotoxic activity

During Helicobacter pylori (Hp) infections, innate immune cells may be positively or negatively modulated by Hp compounds or by Hp-induced cytokines. We have shown previously that the natural cytotoxic activity of PBMC was lower in Hp-infected [Hp(+)] than Hp-uninfected individuals [Hp(-)]. Here, we asked whether the Hp-modulated cytotoxic amplitude is associated with changes in the number of NK cells, their activation or intracellular cytokine expression. Flow cytometry immunophenotyping of PBMC was performed with regard to the surface receptors CD3, CD56 and CD25, and intracellular cytokine expression of IL-2, IFN-γ and IL-10 after in vitro stimulation with Hp glycine acid extract (GE), Hp LPS or standard Escherichia coli LPS. Hp GE-driven enhancement of lymphocyte cytotoxic activity was associated with the expansion of CD3(-)CD56(+)CD25(+) NK cells and the up-regulation of IFN-γ and/or IL-2 synthesis, up to the higher level in Hp(-) than in Hp(+), while Hp LPS-mediated decrease in lymphocyte cytotoxicity was accompanied by the lack of CD3(-)CD56(+)CD25(+) NK propagation, the inhibition of pro-inflammatory cytokine expression and intense expansion of IL-10-producing NK cells. Thus, the cytotoxic and cytokine activities of NK cells were dependent on the type of antigenic challenge and the Hp status, that is, NK cells could be modulated positively by Hp GE Ags and negatively by Hp LPS.

Immunophenotype of peripheral blood natural killer cells and IL-10 serum levels in relation to Helicobacter pylori status

Recent findings suggest that NK (Natural Killer) cells may directly modulate the antimicrobial immune responses. In this study, we performed immunophenotypic analysis of peripheral blood NK cells with regard to CD56, CD16, Nkp46, and CD25 markers, as well as IL-10 levels quantification in the sera samples of asymptomatic, H. pylori (Hp)-infected or uninfected individuals, and combined these results with our previous findings on lymphocyte cytotoxic activity. Twenty healthy volunteers [10 Hp(-);10 Hp(+)] were included in the study. The percentages of classic lymphocytes (CD3(+) ) and NK cells (CD3(-) CD56(+) , CD3(-) Nkp46(+) , CD3(-) CD16(+) ) with or without CD25 receptor were evaluated by fluorochrome-conjugated monoclonal antibody staining and flow cytometry analysis. IL-10 quantification was performed by enzyme-linked immunosorbent assay-ELISA. Our study showed elevated levels of IL-10 and higher NK cell numbers of both CD3(-) CD56(+) CD25(+) and CD3(-) Nkp46(+) CD25(+) phenotypes, as well as CD3(+) CD25(+) classic lymphocytes in Hp(+) compared with Hp(-) individuals. No differences between Hp(-) and Hp(+) individuals were found either in total number of classic lymphocytes or NK cell subtypes. Our data suggest that in Hp(+) donors, there is a domination of lymphocytes and NK cells co-expressing CD25 marker, which might be influenced by the regulatory IL-10. This phenomenon may be a result of H. pylori adaptation to a changing environment in vivo leading to a chronic infection and lack of severe gastric pathologies.

Helicobacter pylori antigens as potential modulators of lymphocytes' cytotoxic activity

Helicobacter pylori (H.p) colonizes human gastric mucosa and causes gastric and duodenal ulcer disease or gastric cancer. Various H.p compounds may modulate the host immune response in regards to tolerance of the infection or disease development. The aim of this study was to determine whether H.p lipopolysaccharide (LPS) and glycine acid extract antigens (GE) or E. coli LPS influence the cytotoxic activity of peripheral blood lymphocytes from H.p infected - H.p (+) or uninfected - H.p (-) individuals, in the presence or absence of exogenous interleukin (IL)12. Individual H.p status was defined by the urea breath test. Lymphocytes, stimulated or not with H.p, and control antigens, with or without IL-12, were used as effector cells and epithelial HeLa cells as targets. The cytotoxicity of lymphocytes was expressed as the percentage of dead target cells unable to reduce tetrazolium salt. The supernatants from HeLa/lymphocyte cultures were used for detection of the cellular cytotoxicity markers granzyme B and caspase 8. The natural cytotoxic activity of lymphocytes from H.p (+) was less than that of H.p (-) donors. This may have been due to fewer natural killer cells of CD3(-) CD56(+) Nkp46(+) phenotype in H.p (+) in comparison to H.p (-) subjects. H.p GE and standard E. coli LPS enhanced the cytotoxicity of lymphocytes towards target cells whereas H.p LPS downregulated this activity. The decrease in lymphocyte cytotoxicity in response to H.p LPS correlated with a lack of IL-2 and IL-12 production, inhibition of interferon-γ production, and low IL-10 secretion by mononuclear leukocytes. IL-12 significantly enhanced the natural as well as H.p LPS and H.p GE driven cytotoxic capacity of lymphocytes. In conclusion, H.p LPS may negatively modulate natural cytotoxic activity and cytokine secretion by immunocompetent cells and thus be involved in the maintenance of infection and development of gastric pathologies.