Major histocompatibility complex class II inhibits fas antigen-mediated gastric mucosal cell apoptosis through actin-dependent inhibition of receptor aggregation.

Escape from normal apoptotic controls is thought to be essential for the development of cancer. During Helicobacter pylori infection, the leading cause of gastric cancer, activation of the Fas antigen (Fas Ag) apoptotic pathway is responsible for early atrophy and tissue loss. As disease progresses, metaplastic and dysplastic glands arise which express Fas Ag but are resistant to apoptosis and are believed to be the precursor cells for adenocarcinoma.

Coinfection modulates inflammatory responses and clinical outcome of Helicobacter felis and Toxoplasma gondii infections.

The host immune response plays a critical role in determining disease manifestations of chronic infections. Inadequate immune response may fail to control infection, although in other cases the specific immune response may be the cause of tissue damage and disease. The majority of patients with chronic infections are infected by more than one organism yet the interaction between multiple active infections is not known, nor is the impact on disease outcome clear.