Expression of CCR2 on monocytes and macrophages in chronically inflamed skin in atopic dermatitis and psoriasis

Monocytes form a significant component of the inflammatory reaction taking place in the skin of atopic dermatitis and psoriasis. Chemokines are pivotal in mediating the attraction of leucocytes to sites of inflammation. The CC-chemokine, monocyte chemotactic protein 1 (MCP-1/CCL2), is expressed by keratinocytes in both atopic dermatitis and psoriasis. MCP-1 binds to the chemokine receptor CCR2 which is known to be expressed on monocytes and macrophages. We examined the expression of CCR2 on peripheral blood monocytes from patients with psoriasis (n=8) and atopic dermatitis (n=7) and found it to be expressed on approximately 90% of the cells, whereas monocytes from healthy donors had a significantly lower CCR2 expression (p<0.05). Skin biopsies from patients suffering from atopic dermatitis and psoriasis revealed that CCR2-positive cells expressed CD163, a marker for monocytes/macrophages. However, not all CD163-positive cells expressed CCR2, which could be interpreted as a mechanism for retaining the macrophages in the skin. Furthermore, we found that keratinocytes are able to express MCP-1, when stimulated with tumour necrosis factor-alpha and/or interferon-gamma in a dose-dependent manner. Thus MCP-1 and CCR2 interaction is likely of importance for the monocyte/macrophage trafficking of inflammatory skin disorders.