Assessment of blood-retina1 barrier integrity

The blood-retina1 barrier consists of two components which are comprised of the retinal vascular endothelium and the retinal pigment epithelium, respectively. Its functional integrity can be recognized by tight junctions between these cells with a paucity of endocytic vesicles within them and the presence of the molecules that regulate the ionic and metabolic gradients that constitute the barrier. The banier is compromised in severa1 disease processes and by a variety of agents, but in most cases the location and mechanism for barrier failure is not understood. Perfusion with a variety of radiolabeled tracer molecules, vitreous fluorophotometry, or magnetic resonance imaging can be used to quantitate blood-retina1 barrier leakage. Fluorescein angiography or magnetic resonance imaging can localize sites of leakage in vivo with limited resolution. Evans blue dye can be used to visualize blood-retina1 barrier failure in gross pathological specimens and immunohistochemical labeling of serum proteins such as albumin or fibrinogen can be used to localize sites of blood-retina1 barrier breakdown by light microscopy. Tracers such as horseradish peroxidase, microperoxidase, or lanthanum, or the immunocytochemical demonstration of albumin can be used to reveal bloodretinal barrier breakdown at the ultrastructural leve1 and provide insights into the mechanisms involved. This review discusses the advantages and lirnitations of each of these methods to aid in selection of the appropriate techniques to derive the desired information

Upregulation of vascular endothelial growth factor (VEGF) in the retinas of transgenic mice overexpressing interleukin-1ß (IL-1ß) in the lens and mice undergoing retinal degeneration

IL-1ß is a pro-inflammatory agent associated with angiogenesis and increased vascular permeability. To determine whether IL-1ß elicits these responses through an upregulation of VEGF, transgenic mice that overexpress IL-1ß in the lens were evaluated at various time points for the localization of VEGF, the location and extent of blood-retinal barrier (BRB) breakdown, and the origin and extent of neovascularization (NV). In homozygous and heterozygous transgenic mice, but not controls, intense VEGF immunoreactivity was scattered throughout the retina at postnatal days 5-7 (P5-7), just after the onset of inflammatory cell infiltration. VEGF staining in the retina remained widespread, but weak from P9-15. Beginning at P15, the intensity of VEGF immunoreactivity achieved a second peak, which it maintained through adulthood. This peak coincided with significant retinal destruction due to massive inflammation. The onset of BRB breakdown coincided with the upregulation of VEGF (P5-7) and widespread BRB breakdown was demonstrated from about P9. From P9-12, aggregates of cells positive for Griffonia simplicifolia isolectin-B4, a marker for vascular endothelial cells, formed on the retinal surface. These cells migrated into the retina at P12-15 with the more superficial cells forming a network of vessels and the deeper cells remaining in small clusters, thus demonstrating that NV occurs much later than BRB breakdown. Non-transgenic FVB/N mice, which undergo retinal degeneration beginning at about P9, also demonstrate the latter peak of VEGF upregulation and the accompanying BRB breakdown, but not the early upregulation. VEGF immunostaining of transgenic and non-transgenic mouse retinas was eliminated by preincubation of the VEGF antibodies with VEGF peptide. The data suggest that the early peak of VEGF upregulation (P5-7) and its accompanying BRB breakdown is due to IL-1ß expression and is likely to be dependent on inflammatory cell infiltration. The latter peak appears to be related to retinal destruction