SummaryA collection of 20 strains of Helicobacter pylori from several regions of the world was studied to better understand the population genetic structure and diversity of this species. Sequences of fragments from seven housekeeping genes (atpA, efp, mutY, ppa, trpC, ureI, yphC ) and two virulence-associated genes (cagA, vacA) showed high levels of synonymous sequence variation (mean percentage K s of 10-27%) and lower levels of non-synonymous variation (mean percentage K a of 0.2-5.6%). Cluster analysis of pairwise differences between alleles revealed the existence of two weakly clonal groupings, which included half of the strains investigated. All six strains isolated from Japanese and coastal Chinese were assigned to the 'Asian' clonal grouping, probably reflecting descent from a distinct common ancestor. The clonal groupings were not totally uniform; recombination, as measured by the homoplasy test and compatibility matrices, was extremely common within all genes tested, except cagA. The fact that clonal descent could still be discerned despite such frequent recombination possibly reflects founder effects and geographical separation and/or selection for particular alleles of these genes.

Studies of Helicobacter pylori from the West have linked production of vacuolating cytotoxin and a particular signal sequence (s1a) allele of the underlying vacA gene to peptic ulcer disease (PUD). Among Chinese H. pylori, most isolates from both PUD and gastritis patients were toxigenic (35/46 and 29/35, respectively). Polymerase chain reaction and DNA sequencing showed that 95 of 96 isolates carried vacA s1a alleles. In the mid-region, 78 of 96 isolates carried m2; 14 were m1-like but only 87% identical (DNA-level) to classical m1 and were designated m1b; the other 4 were unusual hybrids (m1b-type proximal, m2-type distal). Isolates with m1b and m1b-m2 alleles produced higher levels of vacuolating activity than did isolates with m2 alleles (P < .01). There was no association between any vacA allele and disease. These results suggest that the composition of H. pylori gene pools varies geographically and that other as-yet-unknown polymorphic H. pylori genes are important in PUD.

Helicobacter pylori isolates in the Western world possess the cytotoxin-associated gene A (cagA). cagA-positive H. pylori is found to be associated with peptic ulcer disease (PUD) and gastric adenocarcinoma. To investigate the cagA status of H. pylori isolates from Chinese patients with PUD and chronic gastritis (CG), H. pylori populations from 83 patients, 48 with PUD and 35 with CG, were assessed by two different cagA-specific PCRs, Southern blotting, and colony hybridization. The combined results from PCR, Southern blotting, and colony hybridization indicate a prevalence of cagA-positive H. pylori isolates of 98% (47 of 48) among Chinese PUD patients and 100% (35 of 35) among Chinese CG patients. Amplification with primer sets 1 and 2 yielded 52 and 95% of the 82 cagA-positive Chinese H. pylori, respectively. In contrast, the sensitivity of cagA-specific PCR for cagA-positive H. pylori isolates from Dutch patients with primer set 1 was 92% (112 of 122) and that with primer set 2 was 91% (50 of 55). The prevalence of cagA-positive H. pylori populations in Chinese patients with PUD and CG is almost universally high. Therefore, cagA cannot be used as a marker for the presence of PUD in Chinese patients. Our data further suggest that allelic variation in cagA may exist and that distinct H. pylori genotypes may circulate in China and Western Europe.

CD4+ T cells predominate in salivary gland (SG) inflammatory lesions in Sjögren’s syndrome (SS). However, their antigen specificity, degree of clonal expansion, and relationship to clinical disease features remain unknown. We used multiplex reverse-transcriptase PCR to amplify paired T cell receptor α (TCRα) and β transcripts of single CD4+CD45RA− T cells from SG and peripheral blood (PB) of 10 individuals with primary SS, 9 of whom shared the HLA DR3/DQ2 risk haplotype. TCRα and β sequences were obtained from a median of 91 SG and 107 PB cells per subject. The degree of clonal expansion and frequency of cells expressing two productively rearranged α genes were increased in SG versus PB. Expanded clones from SG exhibited complementary-determining region 3 (CDR3) sequence similarity both within and among subjects, suggesting antigenic selection and shared antigen recognition. CDR3 similarities were shared among expanded clones from individuals discordant for canonical Ro and La autoantibodies, suggesting recognition of alternative SG antigen(s). The extent of SG clonal expansion correlated with reduced saliva production and increased SG fibrosis, linking expanded SG T cells with glandular dysfunction. Knowledge of paired TCRα and β sequences enables further work toward identification of target antigens and development of novel therapies.