A novel technique involving radiolabeled monoclonal antibodies was used to characterize and compare the expression of E- and P-selectin on unstimulated, histamine-challenged, and endotoxin-challenged endothelial cells in various tissues of the mouse. Under unstimulated conditions, E-selectin was absent in all organs, but significant expression of P-selectin was observed in several organs. Histamine induced a rapid time-dependent upregulation of P-selectin, with the largest responses observed in mesentery and lung. Significant fold elevations in P-selectin expression occurred as early as 5 minutes after the histamine injection and remained elevated up to 1 hour. Histamine-induced P-selectin upregulation was inhibited by the H 1 receptor antagonist diphenhydramine, whereas the H 2 receptor antagonist cimetidine had no effect. Endotoxin (lipopolysaccharide [LPS]) also induced a time-dependent expression of P-selectin that reached a maximum between 4 and 8 hours after endotoxin administration. LPS-induced upregulation of P-selectin was greatest in heart and stomach, which exhibited insignificant constitutive expression of P-selectin. LPS also induced a time-dependent upregulation of E-selectin, with maximal expression occurring 3 to 5 hours after intraperitoneal administration. The lung and small intestine exhibited the largest responses to LPS challenge. Histamine administration did not affect E-selectin expression in any tissue. E- and P-selectin–deficient mice were used to test the specificity of monoclonal antibody binding in unstimulated, histamine-challenged, and LPS-stimulated tissues. Vascular binding of the radiolabeled E-selectin and P-selectin monoclonal antibodies was not observed in the respective deficient mice. These findings suggest that P-selectin is constitutively expressed on vascular endothelium in some tissues of the mouse and that there are significant regional differences in the magnitude and time course of histamine- and endotoxin-induced P-selectin expression. In contrast, E-selectin appears to be absent on unstimulated vascular endothelium but is upregulated within 3 hours after the administration of endotoxin in most tissues.

Interleukin (IL)-13 has recently been shown to play important and unique roles in asthma, parasite immunity, and tumor recurrence. At least two distinct receptor components, IL-4 receptor (R)α and IL-13Rα1, mediate the diverse actions of IL-13. We have recently described an additional high affinity receptor for IL-13, IL-13Rα2, whose function in IL-13 signaling is unknown. To better appreciate the functional importance of IL-13Rα2, mice deficient in IL-13Rα2 were generated by gene targeting. Serum immunoglobulin E levels were increased in IL-13Rα2−/− mice despite the fact that serum IL-13 was absent and immune interferon γ production increased compared with wild-type mice. IL-13Rα2–deficient mice display increased bone marrow macrophage progenitor frequency and decreased tissue macrophage nitric oxide and IL-12 production in response to lipopolysaccharide. These results are consistent with a phenotype of enhanced IL-13 responsiveness and demonstrate a role for endogenous IL-13 and IL-13Rα2 in regulating immune responses in wild-type mice.

These data show the expression of a novel B7-like molecule on murine ECs that is mediated by IFN-alpha, -beta, and -gamma, and suggest a potential pathway by which ECs may modulate T-cell function.

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Multiple sclerosis (MS) is the most common of the immune demyelinating disorders of the central nervous system (CNS). Leukocyte/endothelial interactions are important steps in the progression of the disease and substances that interfere with these activities have been evaluated as potential therapeutic agents. Cannabinoid receptor agonists have been shown to downregulate immune responses and there is preliminary evidence that they may slow the progress of MS. The purpose of this investigation was to determine how cannabinoid receptor agonists interfere with leukocyte rolling and adhesion. This was investigated in an experimental autoimmune encephalomyelitis (EAE) model using six to eight week old C57BL/6 mice. Mouse myelin oligodendrocyte protein and pertussis toxin were used to induce EAE. WIN 55212-2, CB1 and CB2 antagonist were given. By use of in vivo intravital microscopy, leukocyte/endothelial interactions were evaluated via a cranial window implanted two days before. The results demonstrated that EAE increases leukocyte rolling and firm adhesion in the brain, and that this increased leukocyte/endothelial interaction can be attenuated by administration of WIN 55212-2. Furthermore, use of the selective antagonists for the CB1 receptor (SR 141716A) and the CB2 receptor (SR144528) in this study demonstrated that the cannabinoid's inhibitory effects on leukocyte/endothelial interactions can be mediated by activating CB2 receptor.

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The dual radiolabeled monoclonal antibody technique was used to 1) define the magnitude and kinetics of P-selectin expression in murine small intestine exposed to ischemia-reperfusion (I/R), and 2) determine the factor(s) responsible for initiating this response. Within 10 min after release of a 20-min arterial occlusion, intestinal P-selectin expression increased two- to threefold compared with control values. Peak (4-fold) expression of P-selectin was noted at 5 h after reperfusion, returning to the control value at 24 h. The early (10–30 min) I/R-induced upregulation of P-selectin appears to reflect mobilization of a preformed pool of the adhesion molecule, whereas the later (5 h) rise appears to be transcription dependent. The early increase in P-selectin expression was not inhibited by pretreatment with either oxypurinol (inhibits xanthine oxidase), diphenhydramine (H1-receptor antagonist), or MK-571 (leukotriene C4/D4antagonist), nor was it blunted in transgenic mice expressing three times the normal level of copper-zinc superoxide dismutase or in mast cell-deficient mice. However, significant inhibition was noted after treatment with either MK-886 (5-lipoxygenase inhibitor) or a nitric oxide (NO) donor (diethylenetriamine/NO). These findings indicate that the early I/R-induced increase in intestinal P-selectin expression is mediated by a 5-lipoxygenase-dependent NO-inhibitable mechanism.

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