[Idiopathic proliferative vitreoretinopathy. Activation of microglial cells as the deciding factor].

Mononuclear phagocytes are considered pacemakers in the pathogenesis of proliferative vitreoretinopathy (PVR), but their precise biological origin in preretinal PVR traction membranes has remained obscure. This study presents a combined immunohistochemical protocol for the detection of microglial cells, which was applied to 37 membranes of patients with idiopathic and traumatic PVR and with proliferative diabetic retinopathy (PDR). Microglial cells may be labeled by staining for LN-1, ricinus communis agglutinin-(RCA)-1, vimentin, HLA-DR-II, and nucleoside diphosphatase, but are negative for Leu-M1, Leu-M3, EBM-11, von Willebrand factor, CD22, cytokeratin, and glial fibrillary acidic protein (GFAP). Significant proliferation of microglial cells was found in idiopathic PVR while classical macrophages were typical of traumatic PVR. Only rarely were microglial cells detected in PDR. These findings bring into question previous concepts of the pathobiology of idiopathic PVR and support the hypothesis of idiopathic PVR as a specific disease entity.