Physicochemical characterization and isolation of rabbit kidney-specific autoantigens.

Rabbit kidney tissue contains antigens which are tissue-specific and species restricted, as well as other antigens which are shared by different organs of the animal. The stability of these antigens was investigated as a function of temperature, in order to explore the possibility of thermal fractionation. It was observed that one rabbit kidney-specific autoantigen was destroyed at 56° and another at 65°. A third antigen, which is restricted to the rabbit species but is non-tissue specific, was destroyed at 72°. Ultracentrifugal analysis of the saline extract at different concentrations showed the presence of several components, whose extrapolated values at zero concentration were found to be 4.2S, 6.2S, 10S, 19S, and 80S. The first two components were the most prominent. The rabbit kidney-specific autoantigens were fractionated by a first step of salting out with ammonium sulphate at 4°. The fraction that precipitated in the range from 2.00 to 3.00 M retained most of the antigenic activity. As this fraction was quite impure, it was chromatographed through DEAE-cellulose, then processed through gel filtration columns, using Sephadex G-100 and G-200, and finally purified in agar zone electrophoresis. Two antigens were isolated and both shared similar antigenic characteristics. However, they had slight differences regarding their physico-chemical properties. Sedimentation coefficients of 4.6S and 4.8S were obtained for them. Both antigens possessed a slow electrophoretic mobility, similar to that of the β-globulins. The antigen with higher sedimentation value was slightly faster electrophoretically than the other.