Johannes G. Kusters

Pathogenesis of Helicobacter pylori Infection

SUMMARY Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the worlds population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacteriums ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the hosts immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori.

Regulatory T cells contribute to the impaired immune response in patients with chronic hepatitis B virus infection

Chronic hepatitis B virus (HBV) infection is characterized by a weak immune response to HBV. Regulatory T cells (Treg) can suppress the function of effector T cells and may thus be key players in this impaired immune response. Changes in the functionality or number of Treg could explain the decreased antiviral response in chronic HBV patients. To investigate the role of Treg in chronic HBV infection, we compared the proportional frequency and functionality of Treg in peripheral blood of 50 chronic HBV patients, 23 healthy controls, and 9 individuals with a resolved HBV infection. A higher percentage of Treg, defined as CD4, CD25, CD45RO, and cytotoxic T‐lymphocyte–associated antigen 4–positive cells, was detected within the population of CD4+ cells in peripheral blood of chronic HBV patients compared with healthy controls and individuals with a resolved HBV infection. Accordingly, chronic HBV patients displayed a higher FoxP3 messenger RNA level than healthy controls. Depletion of CD25+ cells from peripheral blood mononuclear cells (PBMC) of chronic HBV patients resulted in an enhanced proliferation after stimulation with HBV core antigen. Reconstitution of these depleted PBMC with CD4+CD25+ Treg resulted in a dose‐dependent reduction of both HBV‐specific proliferation and interferon γ production. In conclusion, chronic HBV patients harbor an increased percentage of Treg in peripheral blood compared with controls. Treg have an immunosuppressive effect on HBV‐specific T helper cells. The presence of HBV‐specific Treg could contribute to an inadequate immune response against the virus, leading to chronic infection. (HEPATOLOGY 2005;41:771–778.)

HELICOBACTER PYLORI AND ANTIMICROBIAL RESISTANCE: MOLECULAR MECHANISMS AND CLINICAL IMPLICATIONS

Helicobacter pylori is an important human pathogen that colonises the stomach of about half of the worlds population. The bacterium has now been accepted as the causative agent of several gastroduodenal disorders, ranging from chronic active gastritis and peptic ulcer disease to gastric cancer. The recognition of H pylori as a gastric pathogen has had a substantial effect on gastroenterological practice, since many untreatable gastroduodenal disorders with uncertain cause became curable infectious diseases. Treatment of H pylori infection results in ulcer healing and can reduce the risk of gastric cancer development. Although H pylori is susceptible to many antibiotics in vitro, only a few antibiotics can be used in vivo to cure the infection. The frequent indication for anti-H pylori therapy, together with the limited choice of antibiotics, has resulted in the development of antibiotic resistance in H pylori, which substantially impairs the treatment of H pylori-associated disorders. Antimicrobial resistance in H pylori is widespread, and although the prevalence of antimicrobial resistance shows regional variation per antibiotic, it can be as high as 95%. We focus on the treatment of H pylori infection and on the clinical relevance, mechanisms, and diagnosis of antimicrobial resistance.

Functional impairment of myeloid and plasmacytoid dendritic cells of patients with chronic hepatitis B

Dendritic cells (DC) play an important role in the induction of T‐cell responses. We hypothesize that the hampered antiviral T‐cell response in chronic hepatitis B patients is a result of impaired dendritic cell function. In this study, we compared the number, phenotype and functionality of two important blood precursor DC, myeloid DC (mDC) and plasmacytoid DC (pDC), of chronic hepatitis B patients with healthy volunteers. No differences in percentages of mDC and pDC in peripheral blood mononuclear cells were observed between chronic hepatitis B patients and healthy controls. The allostimulatory capacity of isolated and in vitro matured mDC, but not of pDC, was significantly decreased in patients compared to controls. Accordingly, a decreased percentage of mDC expressing CD80 and CD86 was observed after maturation, compared to controls. In addition, mDC of patients showed a reduced capacity to produce tumor necrosis factor α after a stimulus with synthetic double‐stranded RNA and interferon γ. Purified pDC from patients produced less interferon α, an important antiviral cytokine, in response to stimulation with Staphylococcus aureus Cowan strain I than pDC isolated from controls. In conclusion, mDC and pDC are functionally impaired in patients with chronic hepatitis B. This might be an important way by which hepatitis B virus evades an adequate immune response, leading to viral persistence and disease chronicity. (HEPATOLOGY 2004;40:738–746.)

Grading of dysplasia in Barrett's oesophagus: Substantial interobserver variation between general and gastrointestinal pathologists

Aims:  To determine interobserver variation in grading of dysplasia in Barretts oesophagus (BO) between non‐expert general pathologists and expert gastrointestinal pathologists on the one hand and between expert pathologists on the other hand.

Quasispecies Development of Helicobacter pylori Observed in Paired Isolates Obtained Years Apart from the Same Host

Helicobacter pylori isolates show greater genetic diversity than other bacterial species studied, but the basis for this phenomenon is unknown. Whether detectable genomic mutation appears within an H. pylori population during persistent colonization was investigated. Paired H. pylori populations obtained across 7- to 10-year intervals from 13 patients were characterized by use of methods including polymerase chain reaction (PCR) genotyping for cagA, vacA, iceA, recA, and IS605; random arbitrarily primed DNA (RAPD)-PCR and amplified fragment length polymorphism (AFLP) analysis; and ELISA, to determine Lewis phenotypes. Genotyping, including recA sequence analysis, revealed that initial and follow-up populations represented the same population in 11 patients (85%). Nevertheless, distinct dissimilarities were shown within each of these 11 pairs by both RAPD-PCR and AFLP analyses. During follow-up, Lewis-y levels, but not Lewis-x levels, decreased significantly. The changes detected by RAPD-PCR and AFLP indicate that genetic drift occurs within H. pylori populations over the course of years of colonization of a single host.

Location of antigenic sites defined by neutralizing monoclonal antibodies on the S1 avian infectious bronchitis virus glycopolypeptide

Neutralizing monoclonal antibodies directed against five antigenic sites on the spike (S) S1 glycopolypeptide of avian infectious bronchitis virus (IBV) were used to select neutralization-resistant variants of the virus. By comparing the nucleotide sequence of such variants with the sequence of the IBV parent strain, we located five antigenic sites on the amino acid sequence of the S1 glycopolypeptide. The variants had mutations within three regions corresponding to amino acid residues 24 to 61, 132 to 149 and 291 to 398 of the S1 glycopolypeptide. The location of three overlapping antigenic sites on the IBV spike protein was similar to the location of antigenic sites on the spike protein of other coronaviruses.

Accurate Prediction of Macrolide Resistance in Helicobacter pylori by a PCR Line Probe Assay for Detection of Mutations in the 23S rRNA Gene: Multicenter Validation Study

ABSTRACT Helicobacter pylori strains from 299 patients were tested in six laboratories in different countries. Macrolide susceptibility of the strains was determined by agar dilution (17.4%) or the epsilometer test (82.6%). Mutations in the 23S ribosomal DNA (rDNA) that are associated with macrolide resistance were analyzed by PCR and reverse hybridization (PCR-line probe assay [LiPA]). This method identifies A2115G, G2141A, A2142G, A2142C, A2142T, A2143G, and A2143C mutations in the 23S rDNA. vacA s-region (s1a, s1b, s1c, and s2) and m-region (m1, m2a, and m2b) genotypes andcagA status were also determined using another PCR-LiPA system. Of the 299 strains investigated by MIC testing, 130 (43.5%) were resistant and 169 (56.5%) were susceptible to clarithromycin. Of the 130 resistant strains, 127 (97.7%) contained 23S rDNA mutations, whereas 167 (98.8%) of the 169 susceptible strains contained wild-type sequences. The predominant mutations were A2143G (45.2%) and A2142G (33.3%). Twenty-eight (19.8%) strains contained multiple 23S rDNA mutations. Only five resistant strains contained the A2142C mutation (three of these in combination with the A2142G mutation), and the A2115G, G2141A, A2142T, and A2143C mutations were not found. MICs of clarithromycin for the A2142G mutant strains were significantly higher than MICs for the A2143G strains. Although there was no significant association between 23S rDNA mutations and the vacA andcagA status, clarithromycin-susceptible strains more often contained mixed vacA genotypes, indicating the presence of multiple H. pylori strains. In conclusion, our data confirmed the very strong association between 23S rDNA mutations and macrolide resistance and showed that the PCR-LiPA permits accurate and reliable diagnosis of macrolide resistance in H. pylori.

Effect of frequent consumption of a Lactobacillus casei-containing milk drink in Helicobacter pylori-colonized subjects.

Background : Several studies have reported inhibitory effects of lactic acid bacteria on bacterial pathogens.

The Helicobacter pylori Homologue of the Ferric Uptake Regulator Is Involved in Acid Resistance

ABSTRACT The only known niche of the human pathogen Helicobacter pylori is the gastric mucosa, where large fluctuations of pH occur, indicating that the bacterial response and resistance to acid are important for successful colonization. One of the few regulatory proteins in the H. pylori genome is a homologue of the ferric uptake regulator (Fur). In most bacteria, the main function of Fur is the regulation of iron homeostasis. However, in Salmonella enterica serovar Typhimurium, Fur also plays an important role in acid resistance. In this study, we determined the role of the H. pylori Fur homologue in acid resistance. Isogenic fur mutants were generated in three H. pylori strains (1061, 26695, and NCTC 11638). At pH 7 there was no difference between the growth rates of mutants and the parent strains. Under acidic conditions, growth of the fur mutants was severely impaired. No differences were observed between the survival of the fur mutant and parent strain 1061 after acid shock. Addition of extra iron or removal of iron from the growth medium did not improve the growth of the fur mutant at acidic pH. This indicates that the phenotype of the fur mutant at low pH was not due to increased iron sensitivity. Transcription of fur was repressed in response to low pH. From this we conclude that Fur is involved in the growth at acidic pH of H. pylori; as such, it is the first regulatory protein implicated in the acid resistance of this important human pathogen.