Circulating Fibrocytes Contribute to the Myofibroblast Population in Proliferative Vitreoretinopathy Epiretinal Membranes

Background/aims: Fibrocytes, circulating cells that co-express markers of haematopoietic stem cells, leucocytes and fibroblast products, traffic to sites of tissue injury, differentiate into myofibroblasts and contribute to wound healing and fibrosis. We investigated the presence of fibrocytes and the expression of their chemotactic pathways CCL21/CCR7 and CXCL12/CXCR4 in proliferative vitreoretinopathy (PVR) epiretinal membranes.

Methods: Sixteen membranes were studied by immunohistochemical techniques.

Results: Cells expressing alpha-smooth-muscle actin (alpha-SMA), a marker of differentiation of fibrocytes into myofibroblasts, were present in all membranes. Cells expressing the haematopoietic stem-cell antigen CD34, the leucocyte common antigen CD45, CCR7, CXCR4, CCL21 and CXCL12 were noted in 50%, 75%, 68.8%, 100%, 80% and 93.8% of the membranes, respectively. Double immunohistochemistry indicated that all cells expressing CD34, CD45, CCR7, CXCR4, CCL21 and CXCL12 co-expressed alpha-SMA. The number of cells expressing CD34 correlated significantly with the numbers of cells expressing CXCL12 (r(s) = 0.567; p = 0.022) and CCL21 (r(s) = 0.534; p = 0.04).

Conclusions: Circulating fibrocytes may function as precursors of myofibroblasts in PVR membranes.