Persistence of Chlamydia trachomatis infections: bacterium and host based?

Reversible inhibition of Chlamydia trachomatis infection in epithelial cells due to stimulation of P2X(4) receptors

Bacterial infections of the mucosal epithelium are a major cause of human disease. The prolonged presence of microbial pathogens stimulates inflammation of the local tissues, which leads to changes in the molecular composition of the extracellular milieu. A well-characterized molecule that is released to the extracellular milieu by stressed or infected cells is extracellular ATP and its ecto-enzymatic degradation products, which function as signaling molecules through ligation of purinergic receptors. There has been little information, however, on the effects of the extracellular metabolites on bacterial growth in inflamed tissues. Millimolar concentrations of ATP have been previously shown to inhibit irreversibly bacterial infection through ligation of P2X(7) receptors. We show here that the proinflammatory mediator, ATP, is released from Chlamydia trachomatis-infected epithelial cells. Moreover, further stimulation of the infected cells with micromolar extracellular ADP or ATP significantly impairs the growth of the bacteria, with a profile characteristic of the involvement of P2X(4) receptors. A specific role for P2X(4) was confirmed using cells overexpressing P2X(4). The chlamydiae remain viable and return to normal growth kinetics after removal of the extracellular stimulus, similar to responses previously described for persistence of chlamydial infection.

A candidate gene approach of immune mediators effecting the susceptibility to and severity of upper gastrointestinal tract diseases in relation to Helicobacter pylori and Epstein-Barr virus infections

This review focuses on immunogenetic aspects of diseases of the upper gastrointestinal tract in which infectious agents may play a role in the aetiopathogenesis, such as Helicobacter pylori, Epstein-Barr virus (EBV) and HIV. Gastric adenocarcinoma is a common cancer all around the world, with declining incidences in Europe and high incidences in Asia and central and south America. Together with gastric atrophy and peptic ulcer disease, gastric adenocarcinoma belongs to the commonest upper gastrointestinal tract diseases. These diseases are multifactorial and factors such as smoking and dietary habits contribute to the pathogenesis. More recently, scientists have turned their eyes on the host. Functional polymorphisms in the genes regulating the host immune system may contribute to the susceptibility to and progression of disease. In multifactorial and polygenetic diseases, candidate gene studies of single nucleotide polymorphisms (SNPs) detect small to moderate relative risks. Unfortunately, only a few functional SNPs have been identified. The candidate gene approach can be seen as a useful first step in exploring causal pathways between genetic determinants and complex diseases such as those mentioned above. To date, little is known about the immunogenetics of upper gastrointestinal tract diseases. We review the literature on H. pylori, EBV and gene polymorphisms that affect key immune mediators influencing the pathogenesis of the inflammatory response, such as the genes that code for the IL-1 family, TNF-alpha, lymphotoxin alpha, and IL-10. IL-1, IL-10, lymphotoxin alpha and TNF-alpha polymorphisms increase the risk of upper gastrointestinal pathogenesis in H. pylori-infected patients, whereas IL-1 and TNF-alpha polymorphisms confer risk in EBV-infected patients.