Anna Massaguer

Concanavalin-A-induced liver injury is severely impaired in mice deficient in P-selectin

P‐selectin (CD62P) is an adhesion molecule that mediates the initial attachment of leukocytes to activated platelets and endothelial cells in damaged tissues. We evaluated the role of P‐selectin in concanavalin A (Con A)‐induced hepatitis, a model characterized by CD4+ T cell activation and infiltration of the liver. Con A injection induced transient P‐selectin expression on hepatic venules and platelets. Mice lacking P‐selectin showed impaired lymphocyte adhesion to liver venules and sinusoids, a striking reduction in intrasinusoidal occlusion, and decreased lymphocyte infiltration of liver parenchyma. The reduction in transaminase levels and the almost complete abolition of necrotic injury demonstrated that liver damage was lower in P‐selectin‐deficient mice. In wild‐type mice, pretreatment with the P‐selectin‐blocking monoclonal antibody attenuated the sinusoidal occlusion and reduced the rise in transaminases after Con A treatment. These results implicate P‐selectin in the development of Con A‐induced liver injury and reveal the protective effect of blocking P‐selectin in this hepatitis.

Trefoil peptide TFF2 treatment reduces VCAM-1 expression and leukocyte recruitment in experimental intestinal inflammation

There is evidence for a beneficial effect of trefoil peptides in animal models of gastric damage and intestinal inflammation, but the optimal treatment strategy and the mechanistic basis have not been explored thoroughly. It has been suggested that these proteins may modulate the inflammatory response. The aims of this study were to compare the protective and curative value of systemic and topical trefoil factor family (TFF)2 administration in dextran sulfate sodium‐induced experimental colitis and to investigate the relationship between the therapeutic effects of TFF2 and modulation of leukocyte recruitment and expression of cell adhesion molecules. Clinical and morphologic severity of colitis was evaluated at the end of the study (Day 10). Leukocyte–endothelial cell interactions were determined in colonic venules by fluorescence intravital microscopy. The expression of cell adhesion molecules vascular cell adhesion molecule 1 (VCAM‐1) and mucosal addressin cell adhesion molecule 1 (MAdCAM‐1) was measured by the dual radiolabeled monoclonal antibody technique. Pretreatment with TFF2 by subcutaneous or intracolonic (ic) route ameliorated the clinical course of colitis, and the luminal route had a significantly superior effect. This beneficial effect was correlated with significant reductions in endothelial VCAM‐1 but not MAdCAM‐1 expression and leukocyte adhesion to intestinal venules, which returned to levels similar to those of controls. In established colitis, ic TFF2 treatment did not modify the severity of colonic lesions. In conclusion, TFF2 is useful in the treatment of colitis, and topical administration is superior to the systemic route. Reduction in adhesion molecule expression and leukocyte recruitment into the inflamed intestine contributes to the beneficial effect of this treatment.

Effect of cyclosporin A on cell adhesion molecules and leukocyte-endothelial cell interactions in experimental colitis.

Background:Cyclosporin A (CsA) is an immunosuppressive agent that is believed to act primarily through effects on T-helper lymphocyte function and proliferation. The aim of this study was to investigate whether modulation of leukocyte recruitment and expression of cell adhesion molecules contribute to the therapeutic efficacy of CsA in a model of experimental colitis. Methods:The therapeutic effects of CsA were assessed in mice with dextran sulfate sodium–induced colitis. Leukocyte-endothelial cell interactions were determined in colonic venules by intravital microscopy. The expression of cell adhesion molecules intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and mucosal addressin cell adhesion molecule 1 (MAd-CAM-1) was measured by the radiolabeled antibody technique. Results:Treatment with CsA (4 mg/kg/day) significantly improved the clinical course of colitis, decreasing weight loss, diarrhea, rectal bleeding, disease activity index, colon weight, and colonic shortening. Microscopic damage score, myeloperoxidase activity, tumor necrosis factor alpha (TNF-&agr;), and interleukin-6 in colonic tissue were significantly diminished by CsA. CsA also significantly reduced ICAM-1 and VCAM-1, but not MAdCAM-1, expression in colitic mice. TNF-&agr;–induced ICAM-1 and VCAM-1 expression in primary cultures of human umbilical vein endothelial cells was reduced by co-incubation with CsA. The reduction in adhesion molecule expression was followed by a marked decrease in leukocyte adhesion in colonic venules of colitic mice. Conclusions:CsA ameliorates experimental colitis in mice. Reduced adhesion molecule expression resulting from diminished pro-inflammatory cytokine production and from a direct effect of CsA in endothelial cells decreases leukocyte recruitment into the inflamed intestine, contributing to this protective effect.

Characterization of platelet and soluble-porcine P-selectin (CD62P)

P-selectin (CD62P), an adhesion molecule expressed on activated endothelial cells and platelets, mediates the initial attachment of leukocytes to the stimulated endothelium upon inflammation and the interaction between leukocytes and platelets. A soluble form of P-selectin is present in the serum of healthy individuals as a circulating protein and high levels have been described in various pathological situations. The aim of this study was to characterize P-selectin on porcine platelets and investigate the soluble form of this protein, which are uncharacterized in several animal species including pigs. A new monoclonal antibody (mAb) (SwPsel.1.9) against porcine P-selectin was produced using a mouse cell line transfected with pig P-selectin cDNA. This mAb together with a previously described mAb (P-sel.KO.2.5), produced in our laboratory, was used to develop an ELISA to quantify porcine P-selectin. No significant levels of soluble-porcine P-selectin were observed in healthy animals. However, the total amount of P-selectin measured in porcine platelets was similar to that found in humans. Increased levels of this circulating protein were detected in the plasma from pigs after allograft implantation. In vitro, P-selectin expression on platelet membrane was rapidly induced by PMA and thrombin, as assessed by flow cytometry. However, these activators did not stimulate the release of soluble P-selectin. Analysis of the proteolytic cleavage of this protein from COS-transfected cells revealed that PMA treatment failed to cause the shedding of membrane-bound P-selectin. These data suggest that porcine P-selectin is a suitable marker for inflammation and that the mechanism involved in the generation of circulating P-selectin is not proteolytic release.

P‐selectin mediates leukocyte rolling in concanavalin‐A‐induced hepatitis

Abstract: Concanavalin‐ A (Con‐A)‐induced hepatitis is an experimental model of human autoimmune hepatitis characterized by leukocyte activation and infiltration of the liver. The aim of the present study was to evaluate the role of P‐selectin on leukocyte–endothelial interactions within the hepatic microvasculature in response to Con‐A.