Identification, quantitation, and purification of a 36 kDa circulating protein associated with active pars planitis

To establish a correlation between the presence of a 36 kDa protein in the blood of patients with pars planitis and to characterize and purify this protein.

Blood samples were obtained from patients with pars planitis and other types of uveitis and from various controls. Samples were treated with polyethelene glycol and protein A and were analyzed on 10% SDS-PAGE for the presence of a 36 kDa protein. Quantitative estimation of the level of this protein was determined by densitometric tracing of the stained gels. Polyclonal antibodies were raised by immunizing New Zealand White rabbits with a mixture of the gel fragment containing the 36 kDa protein (p-36) and complete Freund's adjuvant. These antibodies were used in the immunoaffinity purification of this protein.

The levels of p-36 were sixfold to eightfold higher in 81% of the patients with active pars planitis than in controls (P < 0.05). Furthermore, the levels of this protein correlated with disease activity. A partial amino terminal sequence analysis revealed that p-36 may be a novel protein. It has been purified from the patient's blood using affinity chromatography.

A 36 kDa protein (p-36) is found in elevated concentrations in the blood of many patients with active pars planitis. Its putative role in the etiopathogenesis of pars planitis is unknown.