EGF mediates monocyte chemotaxis and macrophage proliferation and EGF receptor is expressed in atherosclerotic plaques
Introduction
The human epidermal growth factor (EGF) receptor (EGFR, HER-1, ErbB1) is a 170 kDa transmembrane receptor tyrosine kinase [1]. Three other homologous members of the EGF receptor gene family have been described; ErbB2, ErbB3 and ErbB4 [1]. The functional EGF receptor consists of dimeric combinations of these subunits. EGFR ligands include EGF, heparin binding EGF (HB-EGF), transforming growth factor-α (TGF-α), amphiregulin (AR), betacellulin (BTC) and epiregulin (ER) [1]. The other members of the EGF receptor family have differential binding specificities to members of the EGF superfamily [1]. We have produced and characterised a series of rat monoclonal antibodies that specifically recognize the external domain of EGFR/HER-1 [2].
There have been previous reports that cells of the myeloid lineage, for example glial cells [3], tumour-associated macrophages [4], and the human monocytic cell line, U937 [5], express EGFR, but a functional role has not been identified.
The aim of this study was to determine whether the EGF receptor, EGFR, is expressed on peripheral monocytes and/or macrophages, whether or not it mediates cell function and whether there is a potential role for EGFR in atherogenesis.
Section snippets
Reagents
All reagents were purchased from Sigma (Poole, Dorset, UK) unless otherwise stated.
Mononuclear cell & macrophage isolation
Mononuclear cells were isolated from whole blood by density centrifugation using Histopaque 1083(r) (Sigma, Poole, Dorset, UK). Mononuclear cells were incubated in Dulbecco’s Modified Eagles’ Medium containing 10% foetal bovine serum, 50 IU penicillin/ml and 50 μg streptomicin/ml (Gibco, Paisley, Scotland) to allow monocytes to adhere as macrophages. Non-adherent cells were washed off.
Flow cytometry
Whole blood or cell
EGFR is expressed by monocytes and macrophages
EGFR was found to be expressed on the surface of 8.6% of unstimulated rabbit peripheral blood monocytes (Fig. 1a (i)) and 29.1% of unstimulated rabbit monocyte-derived macrophages (Fig. 1a (ii)) using the monoclonal antibody ICR9 by flow cytometry. However, ErbB2 could not be detected on either monocytes (Fig. 1a (iii)) or macrophages (Fig. 1a (iv)) using the monoclonal antibody HM64.
EGF is a monocyte chemokine
We found that EGF-stimulated monocyte migration in a dose-dependent manner in a micro-Boyden chamber (Fig. 1b).
Discussion
Mononuclear cell recruitment is a key aspect of all chronic inflammatory responses, including atherosclerosis. Endothelium-derived chemokines play a central role in monocyte recruitment, and more than 20 monocyte chemokines derived from endothelial cells have been identified [7]. We have demonstrated here that EGF, a factor that may be expressed by the endothelium [8], exhibits chemotactic activity towards monocytes.
Proliferating macrophages have been identified in atherosclerotic lesions from
Acknowledgements
We would like to thank the British Heart Foundation for their financial support.
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