Decay-accelerating factor in guinea pig stomachs following ischemia reperfusion stress

HIF-dependent induction of apical CD55 coordinates epithelial clearance of neutrophils

Sites of inflammation are associated with dramatic shifts in tissue metabolism. Inflammation can result in significant tissue hypoxia, with resultant induction of hypoxia-responsive genes. Given this association, we hypothesized that neutrophil (PMN) ligands expressed on epithelial cells may be regulated by hypoxia. Initial studies confirmed earlier results that epithelial hypoxia enhances PMN transepithelial migration and promotes apical clearance of PMN from the epithelial surface. A screen of known PMN ligands revealed a surprisingly stable expression pattern in hypoxia. However, this screen identified one gene, CD55, as a highly hypoxia-inducible molecule expressed on the apical membrane of mucosal epithelia. Subsequent studies verified the induction of CD55 mRNA and protein expression by hypoxia. Overexpression of CD55 by transfection in nonhypoxic epithelia resulted in a similar pattern of apical PMN clearance, and peptide mimetics corresponding to the PMN binding site on DAF blocked such apical clearance of PMN. Studies directed at understanding molecular pathways of hypoxia inducibility revealed that a approximately 200 bp region of the CD55 gene conferred hypoxia inducibility for CD55. These studies identified a functional binding site for the transcriptional regulator hypoxia-inducible factor (HIF). Taken together, these results identify HIF-dependent induction of epithelial CD55 in the resolution of ongoing inflammation through clearance of apical PMN.

Helicobacter pylori eradication decreases the expression of glycosylphosphatidylinositol-anchored complement regulators, decay-accelerating factor and homologous restriction factor 20, in human gastric epithelium

BACKGROUND

It has previously been reported that there is a strong correlation between the expression of glycosylphosphatidylinositol (GPI)-anchored complement membrane inhibitor in gastric epithelium and the severity of inflammation of gastric mucosa. To investigate the regulation of complement activity in gastric epithelium during Helicobacter pylori (H. pylori)-associated gastritis, the expression of GPI-anchored complement membrane inhibitors, decay-accelerating factor (DAF) and 20-kDa homologous restriction factor 20 (HRF20), and membrane cofactor protein (MCP), which is a transmembrane protein, were evaluated after removal of the H. pylori stimulus. Furthermore, the expression of the complement fragment, C3c, was also investigated.

METHODS

Forty-six patients with epigastric symptoms and endoscopically confirmed peptic ulcer or gastritis who had H. pylori infection of the gastric mucosa were enrolled in the present study. Biopsy specimens were obtained from the gastric antrum and corpus 1 month before and after eradication. Helicobacter pylori infection was determined by the rapid urease test, histology, and culture before eradication, and by histology, culture, and urea breath test after eradication. Gastric biopsy specimens obtained before and after eradication were evaluated for infiltration by neutrophils and mononuclear cells. The expression of complement membrane inhibitors, DAF, HRF20, and MCP and that of the main complement fragment, C3c, was immunohistochemically evaluated.

RESULTS

One month after the eradication of H. pylori, the infiltration by neutrophils and mononuclear cells in the gastric mucosa decreased significantly (P < 0.0001) as compared with that before eradication. The expression of DAF, HRF20, and C3c on gastric mucosal epithelium also significantly decreased in both the antrum and the corpus (P < 0.05) 1 month after eradication. However, no change was observed in the expression of MCP.

CONCLUSIONS

The decrease in the expression of GPI-anchored complement regulator and the complement after removal of a chronic microbial stimulus suggests that the gastric epithelium appears to undergo an aggressive stress of complement during H. pylori infection. Conclusively, DAF and HRF20 may play an important protective role against complement-mediated damage induced by chronic microbial stimuli in such a pathological condition.

Membrane complement regulatory proteins: insight from animal studies and relevance to human diseases

The complement system plays an important role in host defense. However, if not properly regulated, activated complement can also cause significant damage to host tissues. To prevent complement-mediated autologous tissue damage, host cells express a number of membrane-bound complement regulatory proteins. These include decay-accelerating factor (DAF, CD55), membrane cofactor protein (MCP, CD46) and CD59. Recent studies of membrane complement regulatory proteins from various animal species have revealed similarities as well as significant differences from the corresponding human proteins. In this review, we summarize recent advances in this area and contrast the structure, function and tissue distribution of membrane complement regulatory proteins in human and nonprimate mammalian species. We also discuss how the characterization of the animal proteins has provided important clues and might continue to show relevance to the pathogenesis and therapeutics of a number of human diseases.

Gastroduodenal mucosal defense

The gastroduodenal mucosa is a model system of defense with several structural levels and biologic strategies that are closely interrelated with each other to cope with the harmful ingredients of ingested food and the potentially deleterious effects of gastric acid and pepsin. Experimental and clinical research carried out during the review period added to the understanding of each component of the multiple mechanisms of gastroduodenal mucosal protection. In the first place, mucosal integrity is defended by the mucus gel barrier, the epithelial cell barrier, and the immune barrier. The properties of these barriers are maintained by adequate regulation of mucus production, bicarbonate secretion, mucosal microcirculation, and motor activity. These regulatory systems are alarmed by nociceptive neurons and the mucosal immune system which includes chemokine-secreting epithelial cells. The ultimate defense system is rapid repair of the injured mucosa under the control of several growth factors. Progressing insight into the network of mucosal defense not only will improve existing therapies of inflammation and ulceration but also will provide new leads for the management of functional diseases in the gastroduodenal region.