Glucagon-like peptide-2 enhances intestinal epithelial barrier function of both transcellular and paracellular pathways in the mouse.

BACKGROUND AND AIMS: Glucagon-like peptide-2 (GLP-2) is a recently identified potent intestinotrophic factor. We have evaluated the effect of GLP-2 treatment on intestinal epithelial barrier function in mice. METHODS: CD-1 mice were injected subcutaneously with GLP-2 or a protease resistant analogue, h[Gly(2)]GLP-2, twice daily for up to 10 days. Saline injected mice served as controls. Jejunal segments were mounted in Ussing chambers. Tissue conductance was measured and unidirectional fluxes were determined for (i) Na(+) and the small inert probe Cr-EDTA (both transported via the paracellular pathway) and (ii) the macromolecule horseradish peroxidase (HRP, transported via the transcellular pathway). RESULTS: Mice treated with GLP-2 or h[Gly(2)]GLP-2 for 10 days demonstrated significantly reduced intestinal conductance and fluxes of Na(+), Cr-EDTA, and HRP. Electron microscopy confirmed that GLP-2 reduced endocytic uptake of HRP into enterocytes. Functional changes (evident by four hours) preceded morphological changes (evident by 48 hours). CONCLUSIONS: GLP-2 enhances intestinal epithelial barrier function by affecting both paracellular and transcellular pathways and thus may be of therapeutic value in a number of gastrointestinal conditions.

CD4+ T cells mediate superantigen-induced abnormalities in murine jejunal ion transport.

The immunomodulatory properties of bacterial superantigens (SAgs) have been defined, yet comparatively little is known of how SAgs may affect enteric physiology. Staphylococcus aureus enterotoxin B (SEB) was used to examine the ability of SAgs to alter epithelial ion transport. BALB/c mice, severe combined immunodeficient (SCID, lack T cells) mice, or SCID mice reconstituted with lymphocytes or CD4+ T cells received SEB intraperitoneally, and jejunal segments were examined in Ussing chambers; controls received saline only. Baseline short-circuit current (Isc, indicates net ion transport) and Isc responses evoked by electrical nerve stimulation, histamine, carbachol, or forskolin were recorded. Serum levels of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) were measured. SEB-treated BALB/c mice showed elevated serum IL-2 and IFN-gamma levels, and jejunal segments displayed a time- and dose-dependent increase in baseline Isc compared with controls. Conversely, evoked ion secretion was selectively reduced in jejunum from SEB-treated mice. Elevated cytokine levels and changes in jejunal Isc were not observed in SEB-treated SCID mice. In contrast, SCID mice reconstituted with T cells were responsive to SEB challenge as shown by increased cytokine production and altered jejunal Isc responses that were similar to those observed in jejunum from SEB-treated BALB/c mice. We conclude that exposure to a model bacterial SAg causes distinct changes in epithelial physiology and that these events can be mediated by CD4+ T cells.

Changes in murine jejunal morphology evoked by the bacterial superantigen Staphylococcus aureus enterotoxin B are mediated by CD4+ T cells.

Bacterial superantigens (SAgs) are potent T-cell stimuli that have been implicated in the pathophysiology of autoimmune and inflammatory disease. We used Staphylococcus aureus enterotoxin B (SEB) as a model SAg to assess the effects of SAg exposure on gut form and cellularity. BALB/c, SCID (lacking T cells) and T-cell-reconstituted SCID mice were treated with SEB (5 or 100 microg intraperitoneally), and segments of the mid-jejunum were removed 4, 12, or 48 h later and processed for histochemical or immunocytochemical analysis of gut morphology and major histocompatibility complex class II (MHC II) expression and the enumeration of CD3+ T cells and goblet cells. Control mice received saline only. SEB treatment of BALB/c mice caused a time- and dose-dependent enteropathy that was characterized by reduced villus height, increased crypt depth, and a significant increase in MHC II expression. An increase in the number of CD3+ T cells was observed 48 h after exposure to 100 microg of SEB. Enteric structural alterations were not apparent in SEB-treated SCID mice compared to saline-treated SCID mice. In contrast, SEB challenge of SCID mice reconstituted with a mixed lymphocyte population or purified murine CD4+ T cells resulted in enteric histopathological changes reminiscent of those observed in SEB-treated BALB/c mice. These findings implicate CD4+ T cells in this SEB-induced enteropathy. Our results show that SAg immune activation causes significant changes in jejunal villus-crypt architecture and cellularity that are likely to impact on normal physiological processes. We speculate that the elevated MHC II expression and increased number of T cells could allow for enhanced immune responsiveness to other SAgs or environmental antigens.