Selective eosinophil leukocyte recruitment by transendothelial migration and not by leukocyte-endothelial cell adhesion

Cetirizine and levocetirizine inhibit eotaxin-induced eosinophil transendothelial migration through human dermal or lung microvascular endothelial cells

BACKGROUND

Several second-generation antihistamines have documented anti-inflammatory effects which appear independent of H1-receptor blockade. We investigated the inhibitory effect of cetirizine and its active enantiomer levocetirizine on eosinophil transendothelial migration (TEM) through monolayers of normal human dermal microvascular endothelial cells (HMVEC-d) or human lung microvascular endothelial cells (HMVEC-l).

METHODS

HMVEC-d or HMVEC-l were grown to confluence on micropore filters in transwells inserted into a 24-well tissue culture dish. Eosinophils were isolated by density gradient centrifugation and negative immunomagnetic selection. Untreated eosinophils or eosinophils pre-incubated (30 min at 37 degrees C) with a concentration range of cetirizine or levocetirizine (10-5 to 10-9 m) were added to the upper chamber of the transwell which was incubated for 60 min at 37 degrees C. Both spontaneous eosinophil TEM and TEM to 100 ng/mL of human eotaxin in the lower chamber were assessed.

RESULTS

Between 8 and 10% of the eosinophils added to the upper chamber underwent spontaneous TEM through HMVEC-d or HMVEC-l. The addition of eotaxin to the lower chamber enhanced eosinophil TEM through HMVEC-d or HMVEC-l monolayers to over 20%, i.e. an enhanced TEM of approximately 100% in each case. Pre-incubation of eosinophils with cetirizine or levocetirizine dose-dependently inhibited eosinophil TEM to eotaxin through both HMVEC-d or HMVEC-l with total inhibition of eotaxin-induced TEM observed at 10-8 m for HMVEC-d and 10-7 m for HMVEC-l. Both drugs gave a reduced but significant inhibition of eosinophil TEM at lower concentrations. No concentration of cetirizine or levocetirizine had any significant effect on expression of CD11b, CD18 or CD49d by either resting or eotaxin-stimulated eosinophils. Furthermore, no effect on spontaneous eosinophil TEM, or eosinophil viability was seen with any concentration of cetirizine or levocetirizine.

CONCLUSION

Levocetirizine inhibits eotaxin-induced eosinophil TEM through both dermal and lung microvascular endothelial cells suggesting that, like cetirizine, levocetirizine has potential anti-inflammatory effects.

Effect of a specific cysteinyl leukotriene-receptor 1-antagonist (montelukast) on the transmigration of eosinophils across human umbilical vein endothelial cells

BACKGROUND

Leukotrienes have been implicated in the selective infiltration of eosinophils into the bronchial mucosa in asthma.

OBJECTIVE

We studied whether eosinophil transmigration through cultured human umbilical vein endothelial cells (HUVECs) can be blocked by a specific cysteinyl LT1-receptor-antagonist.

METHODS

Unstimulated and stimulated eosinophils from patients with asthma and normal controls were subjected to confluent human umbilical vein endothelial cell (HUVEC) monolayers separating the upper and lower chamber of Transwell culture plates. Unstimulated eosinophils or cells pre-incubated in the presence of the eosinophil activating cytokines GM-CSF or IL-13 were placed in the upper chambers while PAF, a potent chemoattractant factor for eosinophils, was added to the lower chamber. Migration of eosinophils was quantified by a beta-glucuronidase assay.

RESULTS

The assumption that eosinophils express CysLT1 (cysteinyl-leukotriene 1)-receptors was based on our demonstration of mRNA-expression for the CysLT-1-receptor by polymerase chain reaction on purified eosinophils. The chemotactic response to PAF was significantly reduced when eosinophils were pre-incubated with montelukast for 15 min. When eosinophils were pre-incubated with GM-CSF and/or IL-13, the migratory response to PAF was also significantly reduced by montelukast.

CONCLUSION

From these data we conclude that the specific cysteinyl LT1-receptor antagonist montelukast can inhibit PAF-induced eosinophil transmigration through cultured HUVEC monolayers.

Recombinant human platelet-activating factor-acetylhydrolase inhibits airway inflammation and hyperreactivity in mouse asthma model

Numerous in vitro and in vivo studies in both animal models and human asthmatics have implicated platelet-activating factor (PAF) as an important inflammatory mediator in asthma. In a murine asthma model, we examined the anti-inflammatory activities of recombinant human PAF-acetylhydrolase (rPAF-AH), which converts PAF to biologically inactive lyso-PAF. In this model, mice sensitized to OVA by i.p. and intranasal (i.n.) routes are challenged with the allergen by i.n. administration. The OVA challenge elicits an eosinophil infiltration into the lungs with widespread mucus occlusion of the airways and results in bronchial hyperreactivity. The administration of rPAF-AH had a marked effect on late-phase pulmonary inflammation, which included a significant reduction in airway eosinophil infiltration, mucus hypersecretion, and airway hyperreactivity in response to methacholine challenge. These studies demonstrate that elevating plasma levels of PAF-AH through the administration of rPAF-AH is effective in blocking the late-phase pulmonary inflammation that occurs in this murine allergen-challenge asthma model. These results suggest that rPAF-AH may have therapeutic effects in patients with allergic airway inflammation.

Migration of CD18-deficient neutrophils in vitro: evidence for a CD18-independent pathway induced by IL-8

Neutrophils isolated from a child with severe leukocyte adhesion deficiency 1 (LAD1) had a complete absence of expression of the CD11/CD18 beta2 integrin family of adhesion molecules, and were shown to be deficient in the in vitro adhesion and migration properties. However, we found that interleukin-8 (IL8), a potent chemoattractant for neutrophils, and sputum sol phase induced these LAD1 neutrophils to migrate through an endothelial cell layer in vitro, and confirmed that this migration was CD18-independent. These findings add to evidence of CD18-independent mechanisms of neutrophil recruitment, in particular neutrophil infiltration into the lungs, where IL8 may be an important recruitment factor.

Endothelial cells upregulate eosinophil superoxide generation via VCAM-1 expression

BACKGROUND

In vitro eosinophil (EOS) adhesion to recombinant human (rh)-vascular cell adhesion molecule (VCAM)-1 stimulates superoxide anion (O2-) generation and enhances formyl-methionyl-leucyl phenylalanine (FMLP)-activated O2- generation. Therefore, EOS adhesion via VLA-4 to VCAM-1 expressed on endothelium may be instrumental in the selective recruitment and function of EOS in airway inflammation.

OBJECTIVE

We hypothesized that EOS interaction with endothelial cells expressing VCAM-1 will undergo an enhancement in inflammatory function.

METHODS

To determine this possibility, human umbilical vein endothelial cells (HUVEC) were stimulated with either a combination of interleukin (IL)-4 and tumour necrosis factor (TNF)-alpha (100 pM) or medium alone for 24 h; the expression of adhesion proteins on HUVEC and their effect on EOS O2- generation was subsequently determined.

RESULTS

As determined by both enzyme-linked immunosorbent assay and flow cytometry, IL-4 and TNFalpha acted synergistically to induce VCAM-1 expression on HUVEC. Treating HUVEC with IL-4/TNFalpha also increased EOS adhesion and primed subsequent FMLP (0.1 microM) activated EOS O2- generation. Although EOS adhesion was partially inhibited by both antialpha4 and antibeta2 monoclonal antibodies (MoAbs), O2- generation was completely inhibited by either antialpha4 integrin MoAb (HP1/2) or anti-VCAM MoAb (BBIG-V1). Furthermore, enhanced O2- generation, but not adhesion, associated with IL-4 + TNFalpha-treatment of HUVEC was inhibited when EOS were treated with the platelet activating factor (PAF)-antagonist WEB 2086 (20 microM), thus suggesting an involvement of PAF in priming EOS. However, paraformaldehyde fixation of IL-4/TFN-alpha treated HUVEC did not significantly alter EOS function.

CONCLUSIONS

These results suggest EOS adhesion to endothelial cells via an VLA-4/VCAM-1 interaction may be important in the development of the function of this cell. Furthermore, our results suggest that modulation of EOS function involves two priming factors: EOS adhesion to HUVEC expressing VCAM-1 and PAF.

Pharmacological modulation of cell adhesion molecules

Cell adhesion molecules mediate the contact between two cells or between cells and the extracellular matrix. They are essential for morphogenesis, organization of tissues and organs, regulation of immune cell responses and migration of inflammatory cells from the blood vessels into inflamed tissues. Many diseases have been shown to be associated with dysfunction or with overexpression of certain adhesion molecules. Increased cell adhesion molecule function and number are found in clinical disorders in which inflammation and immune cells are involved. Several possible therapeutic agents are described here which have been shown to reduce the expression and/or function of cell adhesion molecules. Anti-adhesion treatment can lead to diminished infiltration and activation of inflammatory immune cells resulting in decreased tissue injury and malfunction.

Human eosinophils migrate across an intestinal epithelium in response to platelet-activating factor

BACKGROUND/AIMS

Transmigration of eosinophils across intestinal epithelia occurs in a variety of mucosal inflammatory disorders and results in the formation of crypt abscesses containing eosinophils. However, the conditions required to drive transepithelial migration of eosinophils are not understood.

METHODS

This study investigated eosinophil migration across intestinal epithelia using purified eosinophils and confluent monolayers of the human intestinal epithelial cell line T84.

RESULTS

Unactivated eosinophils (i.e., no granulocyte/macrophage colony-stimulating factor [GM-CSF] preexposure) did not migrate across T84 monolayers in the presence of transepithelial gradients of C5a, n-formyl-methionyl-leucyl-phenylalanine (fMLP), or platelet-activating factor (PAF). In contrast, activation of eosinophils by coincubation or pretreatment with GM-CSF enabled transepithelial migration in response to PAF but not to C5a or fMLP gradients in a time- and dose-dependent fashion. Specificity was confirmed by both the PAF receptor antagonist WEB-2086 and the PAF enantiomer 2-lyso-beta-acetyl-gamma-O-hexadecyl. Finally, addition of functionally inhibitory monoclonal antibodies to CD11b but not CD11a, very late activation antigen (VLA-4), or intracellular adhesion molecule 1 inhibited eosinophil migration.

CONCLUSIONS

These studies establish that physiologically directed migration of eosinophils across model epithelia occurs but that this process is governed by the state of eosinophil activation, the specific chemotactic gradient imposed, and the availability of specific surface integrins to participate in putative eosinophil-epithelial adhesion steps.

Inhibition of leukocyte adhesion to endothelial cells of human umbilical vein by Y-24180, an antagonist of platelet-activating factor

Effect of Y-24180 (4-(2-chlorophenyl)-2-[2-(4-isobutylphenyl)ethyl]-6,9-dimethyl-6H- thieno [3,2-f][1, 2, 4]triazolo[4,3-a][1,4]diazepine), an antagonist of platelet-activating factor (PAF), on adhesion of leukocytes to endothelial cells of human umbilical vein was examined. Y-24180 inhibited the adhesion of guinea-pig peritoneal exudate cells activated by leukotriene B4 to endothelial cells in a concentration-dependent manner. WEB2086, another PAF antagonist, did not show the inhibitory effect. Inhibition by Y-24180 was not influenced by addition of PAF. Y-24180 had no effect on the expression of intercellular adhesion molecule-1 or endothelial-leukocyte adhesion molecule-1 on endothelial cells activated with interleukin-1 beta, while it suppressed the expression of CD18 antigen on human peripheral blood polymorphonuclear cells activated with leukotrien B4, inhibiting their adhesion to endothelial cells activated with interleukin-1 beta. In oxazolone-induced ear edema in mice, which involves delayed-type hypersensitivity with infiltration by inflammatory cells, Y-24180 dose-dependently inhibited the increase in ear weights, but WEB2086 did not. These results indicate that Y-24180 inhibits not only the actions of PAF but also the adhesion of leukocytes by suppressing the expression of CD18 antigen, inducing the inhibition of infiltration by inflammatory cells.

Mechanisms of eosinophil recruitment

As with other types of leukocytes, mechanisms that function to enable the recruitment of eosinophils into specific sites of immune reactions involve a complex and cumulative interplay of many molecules and pathways. No single chemoattractant is specific for eosinophils, but rather various chemoattractants active on eosinophils can also elicit migration of other specific cell types. Humoral mediators causing eosinophil migration include C5a and platelet-activating factor, whereas cytokines active as eosinophil chemoattractants include interleukin (IL)-2, IL-3, IL-5, granulocyte/macrophage colony-stimulating factor, lymphocyte chemoattractant factor, and RANTES. Eosinophils utilize several pathways to adhere to vascular endothelial cells, including binding to intercellular adhesion molecule-1, E-selectin, and vascular cell adhesion molecule-1 (VCAM-1). The lack of binding of neutrophils to VCAM-1 and the enhanced expression of VCAM-1 elicited by IL-4 contribute to preferential eosinophil accumulation. Eosinophil recruitment is dependent not only on ligands expressed on eosinophils and molecules inducible on endothelial cells but also on processes active during transendothelial migration and extravascular migration in the extracellular spaces.