Interstitial retinol-binding protein (IRBP) in subretinal fluid

Antibodies against bovine interstitial retinol-binding protein (b-IRBP) were used to detect human IRBP (h-IRBP) on immunoblots of eight samples of subretinal fluid (SRF) from patients with retinal detachments of between 2 days' and more than 2 years' duration. Using this sensitive technique, it was found that seven of the samples contained h-IRBP in concentrations estimated to range from below 5% up to 19% of normal human IPM. One of these samples displayed two immunoreactive bands of roughtly equal intensity, one at a molecular weight of 135,000 (h-IRBP), the other at 115,000. The latter may have been generated by proteolytic cleavage. No h-IRBP could be detected in an eighth sample from a patient with retrolental fibroplasia. It is concluded that the reduced concentration of h-IRBP in SRF may be due to a number of factors that include dilution, proteolytic degradation, and metabolic inactivation of photoreceptors at the detachment site.