[Mononuclear phagocytes and their growth factors: pacemakers of proliferative vitreoretinopathy?]

Recent studies on the natural course of proliferative vitreoretinopathy (PVR) have focused on the mononuclear phagocyte system (MPS). Although the precise origin of these cells is not known, current evidence indicates that peripheral blood monocytes infiltrate a lesion initially, subsequently giving way to resident phagocytic cells. In this context the authors try to clarify some aspects of the confusing nomenclature of phagocytic monocytes, macrophages, and microglia. The concept of the blood-retinal barrier (BRB) and its breakdown in PVR are presented and discussed. Platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta), both secretory products of macrophages, have recently been implicated in the development of vitreoretinal pathology. These studies, however, are difficult to evaluate because the biological effects of different growth factors are closely interrelated and vary widely, including both inhibition as well as stimulation of cell growth. The authors hypothesize that plasma of macrophage-derived TGF-beta provokes an increase in fibronectin synthesis, which in turn is responsible for the fibrotic rebuilding of the vitreoretinal interface in PVR. As an adjunct to the pharmacological treatment of PVR with Daunomycin the use of steroids is recommended to suppress the initial macrophage activation and related dysfunction of the BRB.