Inherent potential for production of tumor necrosis factor-alpha by human intestinal macrophages

Functional macrophages and gastrointestinal disorders

Macrophages (MΦ) differentiate from blood monocytes and participate in innate and adaptive immunity. Because of their abilities to recognize pathogens and activate bactericidal activities, MΦ are always discovered at the site of immune defense. MΦ in the intestine are unique, such that in the healthy intestine, they possess complex mechanisms to protect the gut from inflammation. In these complex mechanisms, they produce anti-inflammatory cytokines, such as interleukin-10 and transforming growth factor-β, and inhibit the inflammatory pathways mediated by Toll-like receptors. It has been demonstrated that resident MΦ play a crucial role in maintaining intestinal homeostasis, and they can be recognized by their unique markers. Nonetheless, in the inflamed intestine, the function of MΦ will change because of environmental variation, which may be one of the mechanisms of inflammatory bowel disease (IBD). We provide further explanation about these mechanisms in our review. In addition, we review recent discoveries that MΦ may be involved in the development of gastrointestinal tumors. We will highlight the possible therapeutic targets for the management of IBD and gastrointestinal tumors, and we also discuss why more details are needed to fully understand all other effects of intestinal MΦ.

TREM-1 Promotes Pancreatitis-Associated Intestinal Barrier Dysfunction

Severe acute pancreatitis (SAP) can cause intestinal barrier dysfunction (IBD), which significantly increases the disease severity and risk of mortality. We hypothesized that the innate immunity- and inflammatory-related protein-triggering receptor expressed on myeloid cells-1 (TREM-1) contributes to this complication of SAP. Thus, we investigated the effect of TREM-1 pathway modulation on a rat model of pancreatitis-associated IBD. In this study we sought to clarify the role of TREM-1 in the pathophysiology of intestinal barrier dysfunction in SAP. Specifically, we evaluated levels of serum TREM-1 and membrane-bound TREM-1 in the intestine and pancreas from an animal model of experimentally induced SAP. TREM-1 pathway blockade by LP17 treatment may suppress pancreatitis-associated IBD and ameliorate the damage to the intestinal mucosa barrier.

Two types of tumor necrosis factor-alpha in bluefin tuna (Thunnus orientalis) genes: Molecular cloning and expression profile in response to several immunological stimulants

Tumor necrosis factor-alpha (TNF-alpha) is a key inflammatory mediator and has also the potential as a prominent biomarker of innate immunity. In this study, we identified and characterized TNF-alpha from bluefin tuna, which is an important cultured species. Two types of TNF-alpha were also cloned incidentally (TNF1 and TNF2). The open reading frame of TNF1 and TNF2 cDNA encoded 247 and 245 amino acids, respectively. The amino acid sequence identity among sea perch, red sea bream, and tiger puffer was 73, 70, 59% for TNF1 and 49, 51, 45% for TNF2, respectively. The identity between TNF1 and TNF2 amino acid sequences of the bluefin tuna was only 43%. The positions of cysteine residues, transmembrane sequence, and protease cleavage site in bluefin tuna TNFs were similar with other reported fish and mammalian TNF-alpha. In a phylogenetic analysis, TNF1 is grouped with other reported Perciformes TNF-alpha. On the other hand, TNF2 is grouped with ayu TNF and is quite distant from the fish TNF-alpha group and lymphotoxin-beta group. While TNF1 mRNA showed no significant difference in all tissues, TNF2 mRNA was expressed significantly higher in the blood than in the gill, intestine, head kidney, spleen, heart, and ovary. In peripheral blood leucocytes (PBL), expressions of TNF2 mRNA were significantly increased by stimulation with lipopolysaccharide, phytohemagglutinin, concanavalin A, pokeweed mitogen, phorbol myristate acetate in vitro, but those of TNF1 were not. Recombinant mature TNF1 and TNF2 proteins significantly enhanced phagocytic activity of PBL. Our results suggest that bluefin tuna possess two types of TNF-alpha homologue, and TNF2 is a potential biomarker for innate immunity.

Specific messenger RNA expression for signal transduction molecules by lipopolysaccharide in intestinal macrophages

Intestinal macrophages are known to display profound inflammatory anergy in response to lipopolysacchraide (LPS). To study the mechanisms of unresponsiveness of intestinal macrophages to LPS, we compared the mRNA expression of molecules associated with signal transduction of intestinal macrophages with those of other tissue macrophages. Also cellular localization of CD14 protein was examined. Intestinal, alveolar and peritoneal macrophages were isolated from rats or mice. The expression of mRNA was assessed by real-time PCR, and cellular localization of CD14 protein was examined by flow cytometry. Cellular responses to LPS were examined by production of TNF and NO. The expression of CD14 mRNA in intestinal macrophages was lower than for peritoneal macrophages but higher than for alveolar macrophages. The mRNA expression of other molecules corresponding to intracellular signal transduction in intestinal macrophages was similar with alveolar and peritoneal macrophages. Despite the presence of CD14 mRNA, proteins of CD14 were not detected on cell surfaces of intestinal macrophages, and induction of TNF or NO responding to LPS were not detected. Flow cytometric analysis demonstrated that CD14 protein was not expressed on the cell surface but was expressed inside intestinal macrophages. The unresponsiveness of intestinal macrophages after LPS exposure is considered to be largely attributed to the lack of CD14 protein on their cell surfaces. However, CD14 protein was expressed inside of the cells, suggesting that post-transcriptional regulation rather than transcriptional suppression may play a dominant role in determining the phenotype of the intestinal macrophages.