Purpose: Breakdown of the blood-retinal barrier is a major cause of visual loss in diseases such as diabetic retinopathy, age-related macular degeneration and retinal vein occlusion.
Methods: Human serum, fractionated by gel filtration, was screened for factors that enhance barrier activity by measuring electrical resistance across monolayers of human umbilical vein endothelial cells.
Results: Two peaks of barrier-enhancing activity were detected. The larger peak was broad, contained a preponderance of albumin and increased barrier activity to 183% of controls. The barrier-enhancing properties of the larger peak, however, appeared to be associated with proteins in general and not just albumin. The fractions associated with elution of the larger peak induced maximal increase in resistance in under 1 h, relative to controls. The smaller peak was associated with molecular weights much smaller than those of proteins.