Multiple buoyant densities of hepatitis A virus in cesium chloride gradients

Infectious hepatitis A virus particles produced in cell culture consist of three distinct types with different buoyant densities in CsCl

Although hepatitis A virus (HAV) released by infected BS-C-1 cells banded predominantly at 1.325 g/cm3 (major component) in CsCl, smaller proportions of infectious virions banded at 1.42 g/cm3 (dense HAV particles) and at 1.27 g/cm3 (previously unrecognized light HAV particles). cDNA-RNA hybridization confirmed the banding of viral RNA at each density, and immune electron microscopy demonstrated apparently complete viral particles in each peak fraction. The ratio of the infectivity (radioimmunofocus assay) titer to the antigen (radioimmunoassay) titer of the major component was approximately 15-fold greater than that of dense HAV particles and 4-fold that of light HAV particles. After extraction with chloroform, the buoyant density of light and major component HAV particles remained unchanged, indicating that the lower density of the light particles was not due to association with lipids. Light particles also banded at a lower density (1.21 g/cm3) in metrizamide than did the major component (1.31 g/cm3). Dense HAV particles, detected by subsequent centrifugation in CsCl, were indistinguishable from the major component when first banded in metrizamide (1.31 g/cm3). However, dense HAV particles recovered from CsCl subsequently banded at 1.37 g/cm3 in metrizamide. Electrophoresis of virion RNA under denaturing conditions demonstrated that dense, major-component, and light HAV particles all contained RNA of similar length. Thus, infectious HAV particles released by BS-C-1 cells in vitro consist of three distinct types which band at substantially different densities in CsC1, suggesting different capsid structures with varied permeability to cesium or different degrees of hydration.

Etiopathogenetic aspects of hepatitis A. I. Excretion of hepatitis A virus, biochemistry of liver function, and humoral immune response in patients with hepatitis A on admission to hospital

The excretion of hepatitis A virus (HAV) in stools from 30 patients with clinically overt hepatitis A infection on the day of their admission to the hospital was determined and compared with the dynamics and values of biochemical indices of hepatocyte injury as well as with the immune response to HAV. Virus was found in 16 out of 30 stools (53%) collected within 1 week after the appearance of clinical symptoms. In sera obtained on the day of hospitalization both IgM and IgA anti-HAV were detected in all of the 30 patients, while IgG anti-HAV were found in 20 (67%). There was a correlation between HAV excretion and increasing SGPT upon admission to hospital, while the level of SGPT or bilirubin as well as presence or absence of IgG anti-HAV did not correlate with excretion of HAV. HAV from stools was characterized morphologically and physicochemically. The majority of particles visualized by immune electron microscopy had electrondense appearance, while electron-lucid particles were only occasionally encountered. Isopycnic banding of HAV in CsCl revealed a broad range of densities with HAV activity. Rebanding of pooled fractions containing HAV revealed peak amounts of the virus in fractions with densities 1.32-1.33 gm/cm3.

The electron microscopical and physical characteristics of small round human fecal viruses: an interim scheme for classification

Many of the small round human fecal viruses implicated in outbreaks of nonbacterial gastroenteritis have been collected together and examined under the electron microscope. Negatively stained preparations without the addition of antibody were used so that the surface morphology of the virus particles remained clearly visible. It was apparent that several viruses, previously thought to be simply antigenic variants within the Norwalk group of viruses, show distinct morphological differences and quite clearly belong to other virus groups. By comparing the features of all the viruses examined in this study, both with each other and with standard cell culture strains of enterovirus, parvovirus, and calicivirus, it has been possible to propose an interim classification scheme, based primarily on the morphological appearance of the particles and supported by estimations of size and buoyant density.

Dissociation of hepatitis A virus antigen-anti-HAV antibody complexes by 2-mercaptoethanol and dithiothreitol

Intravenous inoculation of two marmosets and one chimpanzee with hepatitis A virus (HAV) resulted in the replication of virus in liver, excretion of HAV particles in stool, and the appearance of circulating antibodies specific for hepatitis A. The development of an early antibody response in the chimpanzee and in one of the two infected marmosets was shown to interfere with the serologic detection of HAV antigen (HAV Ag) in homogenates of acute phase liver tissue obtained from these animals. Treatment of HAV Ag-positive and IgM anti-HAV-positive liver homogenates with thiol reducing compounds was shown to release HAV Ag from in vitro formed immune complexes. The increased RIA response for HAV Ag in homogenates treated with 2-mercaptoethanol (2-ME) or dithiothreitol (DTT) was further shown not to be due to activation of HAV Ag itself or to a nonspecific effect on the RIA coating antibody, radiolabeled probe, or homogenized liver tissue. IgG and IgM double-antibody sandwich RIAs for HAV Ag were also compared for their ability to detect HAV Ag under reducing and nonreducing conditions. Application of the 2-ME or DTT treatment procedure to the serologic detection of other viral antigens or viruses whose presence in blood, stool, tissue macerate, or other milieu may be masked by specific antibody appears to be feasible.

Hepatitis A virus infection: pathogenesis and serodiagnosis of acute disease

The early development of immune electron microscopic (IEM) methods for the detection of HAV in acute-phase stool suspensions and antibody to HAV (anti-HAV) in serum made it possible to serologically identify cases of hepatitis A using paired acute and convalescent phase sera. Introduction of less cumbersome and time-consuming serologic test methods, including complement fixation (CF) and immune adherence hemagglutination (IAHA), made it feasible to rapidly assay larger numbers of specimens for HAV or anti-HAV. Subsequent development of sensitive immunofluorescence (IF) assays, solid-phase radioimmunoassays (RIA), and enzyme immunoassays (EIA) for HAV and anti-HAV heralded intensive laboratory studies of the biophysical and biochemical properties of the virus as well as efforts to define the pathogenesis and clinical course of disease. Results of the latter studies showed that the bulk of HAV was usually excreted in stool before the onset of clinical symptoms. Other serologic studies demonstrated that all acutely ill patients had circulating anti-HAV IgM, while all convalescent patients were positive for anti-HAV IgG. The development of sensitive serologic tests (RIA and EIA) that could differentiate between anti-HAV IgM and IgG made it possible to serodiagnose an acute case of hepatitis A using a single-phase serum specimen.

A radioimmunoassay for hepatitis A antigen and antibody

The HAVAB radioimmunoassay for the detection of antibody to hepatitis A is assessed. Its modification to detect virus in faecal samples is described and in this it was found to be more sensitive and specific than electron microscopy.

Biochemical and biophysical characterization of light and heavy density hepatitis A virus particles: evidence HAV is an RNA virus

Heavy density HAV was also shown to be sensitive to low concentrations of RNase. The results of these biophysical and biochemical studies strongly support the notion HAV is an enterovirus.