Immunolocalization of the complement component C1q in the mucous membrane of the human duodenum (duodenitis II-III degree)

In order to establish the supposed role of the complement system in the regulation of homeostasis and defense reactions in the intestinal epithelium, an immunofluorescent analysis was conducted of localizing the C1q complement component in the inflamed mucosa of the human duodenum (DM) (duodenitis II-III degree) using C1q-specific antibodies. The findings suggest a pronounced presence of the C1q complement component in various DM areas during inflammation, both in the epithelial layer and in the lamina propria, where C1q is localized in the region of the basolateral membrane of enterocytes and some free cells, presumably neutrophils, macrophages and mast cells. A C1q-specific reaction in the epithelial cells and secretory ducts of the duodenal glands indicates a possible secretion of C1q. Co-localization of C1q, cathepsin G and cell adhesion proteins in the DM epithelium implies their interaction in the regulation of tissue metabolism, modification and maintenance of the barrier properties of the intestinal epithelium in normal and with inflammation.

Different Forms of TFF2, A Lectin of the Human Gastric Mucus Barrier: In Vitro Binding Studies

Trefoil factor family 2 (TFF2) and the mucin MUC6 are co-secreted from human gastric and duodenal glands. TFF2 binds MUC6 as a lectin and is a constituent of the gastric mucus. Herein, we investigated human gastric extracts by FPLC and identified mainly high- but also low-molecular-mass forms of TFF2. From the high-molecular-mass forms, TFF2 can be completely released by boiling in SDS or by harsh denaturing extraction. The low-molecular-mass form representing monomeric TFF2 can be washed out in part from gastric mucosa specimens with buffer. Overlay assays with radioactively labeled TFF2 revealed binding to the mucin MUC6 and not MUC5AC. This binding is modulated by Ca2+ and can be blocked by the lectin GSA-II and the monoclonal antibody HIK1083. TFF2 binding was also inhibited by Me-β-Gal, but not the α anomer. Thus, both the α1,4GlcNAc as well as the juxtaperipheral β-galactoside residues of the characteristic GlcNAcα1→4Galβ1→R moiety of human MUC6 are essential for TFF2 binding. Furthermore, there are major differences in the TFF2 binding characteristics when human is compared with the porcine system. Taken together, TFF2 appears to fulfill an important role in stabilizing the inner insoluble gastric mucus barrier layer, particularly by its binding to the mucin MUC6.

Ca2+signaling in porcine duodenal glands by muscarinic receptor activation

The duodenal glands have been thought to play an important role in defense against proximal duodenal ulcer; however, the secretory mechanisms of these glands remain to be determined. In isolated duodenal acinar cells of the pig, we investigated the effects of ACh on intracellular Ca2+concentration ([Ca2+]i) and on membrane currents with fura 2 fluorometry and the patch clamp technique. ACh caused a transient increase in [Ca2+]i, and the increase was markedly inhibited by atropine or 4-diphenylacetoxy- N-methylpiperidine methiodide but not by hexamethonium, pirenzepine, or methoctramine. The expression of mRNA for the M3subtype far exceeded that for either M1or M2as revealed by real-time quantitative PCR and in situ hybridization. The rise in [Ca2+]ievoked by ACh was largely inhibited by thapsigargin but slightly affected by extracellular Ca2+deprivation. Caffeine had no effect on [Ca2+]i. ACh elicited Ca2+-dependent K+currents, a finding similar to the response to inositol 1,4,5,-trisphosphate applied intracellularly. These results suggest the presence of M3receptors linked to Ca2+release in porcine duodenal glands.