Immune responses to mucosal infection: the Helicobacter pylori paradigm

Fighting a losing battle: vigorous immune response countered by pathogen suppression of host defenses in the chytridiomycosis-susceptible frog Atelopus zeteki

The emergence of the disease chytridiomycosis caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd) has been implicated in dramatic global amphibian declines. Although many species have undergone catastrophic declines and/or extinctions, others appear to be unaffected or persist at reduced frequencies after Bd outbreaks. The reasons behind this variance in disease outcomes are poorly understood: differences in host immune responses have been proposed, yet previous studies suggest a lack of robust immune responses to Bd in susceptible species. Here, we sequenced transcriptomes from clutch-mates of a highly susceptible amphibian, Atelopus zeteki, with different infection histories. We found significant changes in expression of numerous genes involved in innate and inflammatory responses in infected frogs despite high susceptibility to chytridiomycosis. We show evidence of acquired immune responses generated against Bd, including increased expression of immunoglobulins and major histocompatibility complex genes. In addition, fungal-killing genes had significantly greater expression in frogs previously exposed to Bd compared with Bd-naïve frogs, including chitinase and serine-type proteases. However, our results appear to confirm recent in vitro evidence of immune suppression by Bd, demonstrated by decreased expression of lymphocyte genes in the spleen of infected compared with control frogs. We propose susceptibility to chytridiomycosis is not due to lack of Bd-specific immune responses but instead is caused by failure of those responses to be effective. Ineffective immune pathway activation and timing of antibody production are discussed as potential mechanisms. However, in light of our findings, suppression of key immune responses by Bd is likely an important factor in the lethality of this fungus.

Antigastric autoantibodies in Helicobacter pylori infection: role in gastric mucosal inflammation

The aim of the study was to ascertain whether there is an association between the presence of serum parietal cell autoantibodies (PCA) and: (1) Helicobacter pylori infection; (2) the presence and degree of gastritis and intestinal metaplasia; and (3) the H. pylori infecting strain. Gastric mucosal biopsies were obtained from 49 consecutive patients in order to assess and grade gastritis, make a histological diagnosis, and culture and genotype H. pylori. H. pylori infection was present in 26 patients (group 1), had been present in 17 patients (group 2), and the remaining 6 (group 3) had never had the infection. The infecting strain was cagA positive in 21 of 26 group 1 patients. Positive PCA results were found in 84%, 76%, and 14% of patients in groups 1, 2, and 3, respectively. PCA results were correlated with anti-H. pylori antibody titers (P<0.05). In group 2 patients, PCA were associated with the degree of antral gastritis (Fisher's exact test P<0.05). cagA status was not associated with the presence of PCA (chi2=0.68, NS). The frequency of positive findings for PCA in group 2 was higher in patients with (90%) than in those without (50%) intestinal metaplasia.

IN CONCLUSION

(1) H. pylori infection is associated with the production of PCA, which, after eradication of the infection, persist and might contribute to the persistent antral chronic gastritis and intestinal metaplasia; (2) the gastric lesions associated with infections sustained by the more-virulent H. pylori strains do not appear to be due to the induction of antigastric autoantibodies.

Characteristics of gastric-vein lymphocytes with regard to the immune response to Helicobacter pylori

BACKGROUND

Between peripheral blood and tissue-infiltrating lymphocytes there is an intermediate compartment, the blood of the organ-draining vessels, which could show unusual features. The aim of the present study was to analyse the characteristics of the lymphocytes from the stomach-draining vessels and the cytokine secretion by these lymphocytes. The CagA-mediated lymphocyte activation in Helicobacter pylori-infected subjects and the humoral response to this antigen were evaluated and correlated with clinical data.

METHODS

We studied lymphocyte proliferation either with mitogens or with the CagA antigen and cytokine production and IgG anti-CagA by means of an enzyme-linked immunosorbent assay in peripheral blood and gastric-vein blood obtained during surgical intervention.

RESULTS

We showed higher proliferative response and cytokine production in lymphocytes from the gastric vein. The mitogenic response to the CagA antigen was highly specific but poorly sensitive for the H. pylori infection in both the compartments. The overall cytokine profile in our patients affected by non-ulcer disease was of the Th0 type.

CONCLUSIONS

Gastric-vein-derived lymphocytes seem to show unusual features, as they behave like peripheral blood lymphocytes but show higher responses to all the tested stimuli. It is possible that the interaction of the lymphocytes with the mucosal environment could activate the synthetic mechanisms, making the cells more 'responsive' to the stimulation. The CagA antigen is able to induce a specific T-lymphocyte response and is therefore a valid candidate antigen for the development of a vaccine.

Immune responses of specific-pathogen-free mice to chronic Helicobacter pylori (strain SS1) infection

A model permitting the establishment of persistent Helicobacter pylori infection in mice was recently described. To evaluate murine immune responses to H. pylori infection, specific-pathogen-free Swiss mice (n = 50) were intragastrically inoculated with 1.2 x 10(7) CFU of a mouse-adapted H. pylori isolate (strain SS1). Control animals (n = 10) received sterile broth medium alone. Animals were sacrificed at various times, from 3 days to 16 weeks postinoculation (p.i.). Quantitative culture of gastric tissue samples from inoculated mice demonstrated bacterial loads of 4.0 x 10(4) to 8 x 10(6) CFU per g of tissue in the animals. Infected mice had H. pylori-specific immunoglobulin M (IgM) and IgG antibodies in serum (at day 3 p.i.) and IgG and IgA antibodies in their gastric contents (weeks 4 and 16 p.i.) and saliva (week 16 p.i.). Mucosal IgM antibodies were not detected. Histological examination of the gastric mucosae from control and infected mice revealed mild chronic gastritis, characterized by the presence of polymorphoneutrophil cell infiltrates and submucosal lymphoid aggregates, in infected animals at 16 weeks p.i. Differences in the quantities of IgG1 and IgG2a subclass antibodies detected in the sera of mouse strains (Swiss, BALB/c, and C57BL/6) infected by H. pylori suggested that host factors influence the immune responses induced against this bacterium in the host. In conclusion, immune responses to H. pylori infection in mice, like those in chronically infected humans, appear to be ineffective in resolving the infection.