Hepatitis A virus was purified from fecal specimens obtained from 3 patients with naturally acquired hepatitis A, by a process of differential centrifugation, chloroform extraction, column chromatography, and isopycnic ultracentrifugation. Analysis of purified virus by discontinuous SDS-PAGE revealed three major polypeptides with molecular weights of 34,000, 25,500, and 23,000 daltons. These polypeptides appear to be specific for hepatitis A virus and have similar molecular weights to three of the four major polypeptides reported for members of the genus Enterovirus within the family Picornaviridae.

Virus-like particles, 27 nm in diameter, were visualized in stool specimens collected from 8 out of 9 patients with hepatitis A during the acute phase of their illness. No such particles were observed in stools from 3 patients in the acute phase of hepatitis B infection, nor in stools from 9 non-hepatitis patients. When sera from patients suffering a variety of liver diseases were coded and tested by immune electron microscopy for antibody to these 27-nm particles, seroconversion was demonstrated only in patients with hepatitis A. The presence of crystalline arrays of 27-nm particles in one stool specimen has possible significance in the pathogenesis of hepatitis A.

Hepatitis A virus was purified from fecal specimens obtained from 2 patients with naturally acquired hepatitis A. The purification procedure involved differential centrifugation, organic solvent extraction, agarose gel filtration, ion-exchange chromatography, and isopycnic ultracentrifugation in cesium chloride. Using immune electron microscopy and discontinuous SDS-PAGE, this procedure was found to be effective in removing extraneous material from hepatitis A virus. There was significant recovery of virus as judged by immune electron microscopy and solid-phase radioimmunoassay. Using this protocol, it has been possible to obtain virus preparations of sufficient purity and high enough titer to enable biochemical studies to proceed.

A specific IgM response to hepatitis A virus was detected in sera from patients suffering acute hepatitis A infection. The presence of virus-specific IgM in 19S components of acute and early convalescent phase sera was detected by immune electron microscopy and solid-phase radioimmunoassay. The presence of virus-specific IgM in whole serum specimens was demonstrated by indirect immunoferritin labeling. Following acute infection, however, the major immunoglobuhn response appears to be IgG, since titers of specific 7S and whole serum antibody were very similar.

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