An antigen/antibody system specific for an epidemic non‐A, non‐B hepatitis in patients of a cardiovascular surgical unit

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Abstract
The antigen/antibody systems specific for non‐A, non‐B hepatitis (NANB) were studied using urine samples as the antigen source and sera for the antibody source. Two immunologically distinct systems, SO‐antigen/anti‐SO and MI‐antigen/anti‐MI were discovered. This paper deals chiefly with the characterization of the SO‐antigen, which was associated with an epidemic‐type non‐A, non‐B hepatitis found during September 1979 to February 1980 (first outbreak) and October 1980 to January 1981 (second outbreak) in the Cardiovascular Surgical Unit of Tohoku University Hospital. All patients who developed non‐A, non‐B hepatitis during the first and second epidemic periods had SO‐antigen in their urine (24 out of 24). After the epidemic, however, the detection rate of SO‐antigen gradually decreased among patients in the same unit, although posttransfusion non‐A, non‐B hepatitis continued to be found. The initial detection of SO‐antigen occurred at or just after the elevation of alanine aminotransferase (ALT) levels during the episode of hepatitis and persisted in most cases throughout the elevated period. Anti‐SO antibody was detected relatively late (eight months after blood transfusion, in most cases) and apparently persisted longer than five years. The immunological and physicochemical properties of SO‐antigen were also studied. It appeared to be neither a plasma protein nor a liver tissue component when the crossreactivity of SO‐antigen was examined by the immunodiffusion method. Absorption with insolubilized human serum and liver tissues failed to affect the anti‐SO antibody activity. The molecular weight of SO‐antigen was estimated to be 250,000, the sedimentation coefficient to be 11.0 S, and the buoyant density in CsCl to be 1.215 g/cm3. Electron microscopy showed that the SO‐antigen corresponded with uniform particles with a mean diameter of 11 nm. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) analysis of SO‐antigen revealed only a single protein band corresponding to molecular weight 38,000.