Endothelial cells upregulate eosinophil superoxide generation via VCAM-1 expression

Authors


Sedgwick University of Wisconsin Hospital and Clinics, Allergy Section H6/367 CSC, 600 Highland Ave., Madison, WI 53792–3244, USA.

Abstract

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)-α (100 p M) 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 TNFα acted synergistically to induce VCAM-1 expression on HUVEC. Treating HUVEC with IL-4/TNFα also increased EOS adhesion and primed subsequent FMLP (0.1 μM) activated EOS O2 generation. Although EOS adhesion was partially inhibited by both antiα4 and antiβ2 monoclonal antibodies (MoAbs), O2 generation was completely inhibited by either antiα4 integrin MoAb (HP1/2) or anti-VCAM MoAb (BBIG-V1). Furthermore, enhanced O2 generation, but not adhesion, associated with IL-4 + TNFα-treatment of HUVEC was inhibited when EOS were treated with the platelet activating factor (PAF)-antagonist WEB 2086 (20 μM), thus suggesting an involvement of PAF in priming EOS. However, paraformaldehyde fixation of IL-4/TFN-α 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.

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