Colonization of the mucosa of the stomach and the duodenum by Helicobacter pylori is the major cause of acute and chronic gastroduodenal pathologies in humans. Duodenal ulcer formation strongly correlates with the expression of an antigen (CagA) that is usually coexpressed with the vacuolating cytotoxin (VacA), a protein that causes ulceration in the stomach of mice. However, the relationship between these two virulence factors is unknown. To define whether CagA and VacA are coexpressed in all clinical isolates and their relationships, we collected 43 clinical isolates of H. pylori and studied their genetic and phenotypic properties. Based on this analysis, most of the strains could be classified into two major types. Type I bacteria had the gene coding for CagA and expressed the CagA protein and the vacuolating cytotoxin. Type II bacteria did not have the gene coding for CagA and did not express either the CagA protein or the vacuolating cytotoxin. Type I and type II bacteria represented 56 and 16%, respectively, of the 43 clinical isolates, while the remaining 28% had an intermediate phenotype, expressing CagA independently of VacA or vice versa. This finding shows that although it is present in most cytotoxic strains, CagA is not necessary for the expression of the vacuolating cytotoxin.

We show that solid and liquid media, supplemented only with cyclodextrins and free of blood and its derivatives, support the growth of Helicobacter pyloyi. These media can be used for primary isolation of the bacteria from biopsy samples, routine laboratory growth, and large-scale industrial fermentation.

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Colonization of human gastric mucosa with cytotoxic strains of the bacterium Helicobacter pylori is associated with peptic ulcer and with chronic gastritis. Since little is known about the T-cell response to H. pylori, we investigated the CD4 ؉ T-cell response both in peripheral blood mononuclear cells (PBMCs) and at the site of infection. First, we compared the bulk PBMC proliferative response to the bacterium in individuals with and without symptoms of gastroduodenal disease. We found that the PBMCs from virtually all individuals proliferate in response to heat-inactivated bacteria. Second, we cloned H. pylori-specific CD4 ؉ T lymphocytes from the PBMCs of three patients and from both the gastric mucosa and PBMCs of a fourth patient. We have found that CD4 ؉ T-cell clones specific for H. pylori from peripheral blood samples and gastric mucosae of infected patients are major histocompatibility complex class II restricted and discriminate between several cytotoxic and noncytotoxic bacterial strains. Moreover, they are polyclonal in terms of T-cell receptor usage and major histocompatibility complex restriction. Our results demonstrate that the T-cell response to the whole bacterium in PBMCs does not correlate with antibody response, infection, or disease. However, H. pylori-specific CD4 ؉ T cells are detectable, at the clonal level, in both the periphery and gastric mucosa of infected patients. Localization of these cells at the site of disease suggests they are effectors of the immune response to the bacteria.