Predominant infiltration of monocytes in chronic graft-versus-host disease.

Pathogenesis of chronic graft-versus-host disease (cGVHD) is largely unknown. It is important to determine the responsible cell types and the factors that play roles to recruit these cells into sites of disease. We examined whether monocytes and chemokine fractalkine/receptor CX3CR1 axis might be involved. We found that the absolute number of CX3CR1+ monocytes in the blood was significantly decreased in patients with severe cGVHD. Immunohistochemical staining revealed the extensive infiltration of CD14+ cells as well as strong expression of fractalkine in the cGVHD skin. The number of infiltrated CD14+ cells on the margin of fractalkine+ epidermis was larger in cGVHD skin compared to that of acute graft-versus-host disease, whereas no difference was observed in CD3+ T cells. These results suggest that CX3CR1+ monocytes may be recruited from the circulation to the fractalkine+ epidermis in cGVHD, and highlight these cells and this chemokine/receptor axis as additional targets for cGVHD therapy.