Detection and quantitation of hepatitis B surface antigen immune complexes (HBsAg-ICs) by an antigen-specific method. II. Circulating immune complexes (CICs) in patients with hepatitis B and asymptomatic HBsAg carriers

Antibody responses during hepatitis B viral infection

Hepatitis B is a DNA virus that infects liver cells and can cause both acute and chronic disease. It is believed that both viral and host factors are responsible for determining whether the infection is cleared or becomes chronic. Here we investigate the mechanism of protection by developing a mathematical model of the antibody response following hepatitis B virus (HBV) infection. We fitted the model to data from seven infected adults identified during acute infection and determined the ability of the virus to escape neutralization through overproduction of non-infectious subviral particles, which have HBs proteins on their surface, but do not contain nucleocapsid protein and viral nucleic acids. We showed that viral clearance can be achieved for high anti-HBV antibody levels, as in vaccinated individuals, when: (1) the rate of synthesis of hepatitis B subviral particles is slow; (2) the rate of synthesis of hepatitis B subviral particles is high but either anti-HBV antibody production is fast, the antibody affinity is high, or the levels of pre-existent HBV-specific antibody at the time of infection are high, as could be attained by vaccination. We further showed that viral clearance can be achieved for low equilibrium anti-HBV antibody levels, as in unvaccinated individuals, when a strong cellular immune response controls early infection.

Molecular mechanisms underlying occult hepatitis B virus infection

Chronic hepatitis B virus (HBV) infection is a complex clinical entity frequently associated with cirrhosis and hepatocellular carcinoma (HCC). The persistence of HBV genomes in the absence of detectable surface antigenemia is termed occult HBV infection. Mutations in the surface gene rendering HBsAg undetectable by commercial assays and inhibition of HBV by suppression of viral replication and viral proteins represent two fundamentally different mechanisms that lead to occult HBV infections. The molecular mechanisms underlying occult HBV infections, including recently identified mechanisms associated with the suppression of HBV replication and inhibition of HBV proteins, are reviewed in detail. The availability of highly sensitive molecular methods has led to increased detection of occult HBV infections in various clinical settings. The clinical relevance of occult HBV infection and the utility of appropriate diagnostic methods to detect occult HBV infection are discussed. The need for specific guidelines on the diagnosis and management of occult HBV infection is being increasingly recognized; the aspects of mechanistic studies that warrant further investigation are discussed in the final section.

Molecular mechanisms underlying occult hepatitis B virus infection

Chronic hepatitis B virus (HBV) infection is a complex clinical entity frequently associated with cirrhosis and hepatocellular carcinoma (HCC). The persistence of HBV genomes in the absence of detectable surface antigenemia is termed occult HBV infection. Mutations in the surface gene rendering HBsAg undetectable by commercial assays and inhibition of HBV by suppression of viral replication and viral proteins represent two fundamentally different mechanisms that lead to occult HBV infections. The molecular mechanisms underlying occult HBV infections, including recently identified mechanisms associated with the suppression of HBV replication and inhibition of HBV proteins, are reviewed in detail. The availability of highly sensitive molecular methods has led to increased detection of occult HBV infections in various clinical settings. The clinical relevance of occult HBV infection and the utility of appropriate diagnostic methods to detect occult HBV infection are discussed. The need for specific guidelines on the diagnosis and management of occult HBV infection is being increasingly recognized; the aspects of mechanistic studies that warrant further investigation are discussed in the final section.

Drastic reduction in the production of subviral particles does not impair hepatitis B virus virion secretion

Hepatitis B virus (HBV) contains three coterminal envelope proteins on the virion surface: large (L), middle (M), and small (S). The M and S proteins are also secreted as empty "subviral particles," which exceed virions by at least 1,000-fold. The S protein serves as the morphogenic factor for both types of particles, while the L protein is required only for virion formation. We found that cotransfecting replication constructs with a small dose of the expression construct for the missing L, M, and S proteins reconstituted efficient virion secretion but only 5 to 10% of subviral particles. The L protein inhibited secretion of subviral particles in a dose-dependent manner, whereas a too-high or too-low L/S protein ratio inhibited virion secretion. Consistent with the results of cotransfection experiments, a point mutation at the -3 position of the S gene AUG codon reduced HBsAg secretion by 60 to 70% but maintained efficient virion secretion. Surprisingly, ablating M protein expression reduced virion secretion but markedly increased the maturity of virion-associated genomes, which could be reversed by providing in trans both L and M proteins but not just M protein. M protein stability was dependent on the coexpression of S protein. Our findings suggest that efficient HBV virion secretion could be maintained despite drastic reduction in subviral particle production, which supports the recent demonstration of separate secretion pathways adopted by the two types of particles. The M protein appears to facilitate core particle envelopment, thus shortening the window of plus strand DNA elongation.

Antigen-antibody dissociation in Alzheimer disease: a novel approach to diagnosis

With the ever-increasing population of aged individuals at risk of developing Alzheimer's disease (AD), there is an urgent need for a sensitive, specific, non-invasive, and diagnostic standard. The majority of efforts have focused on auto-antibodies against amyloid-beta (Abeta) protein, both as a potential treatment, and a reliable biomarker of AD pathology. Naturally occurring antibodies against Abeta are found in the CSF and plasma of patients with AD as well as healthy control subjects. To date, differences between diseased and control subjects have been highly variable. However, some of the antibody will be in preformed antigen-antibody complexes and the extent and nature of such complexes may provide a potential explanation for the variable results reported in human studies. Thus, measuring total amounts of antigen or antibody following unmasking is critical. Here, using a technique for dissociating antibody-antigen complexes, we found significant differences in serum antibodies to Abeta between AD and aged-matched control subjects. While the current study demonstrates the relevance of measuring total antibody, bound and unbound, against Abeta in AD, this technique may be applicable to diseases such as acquired immune deficiency syndrome and hepatitis B where determination of antigen and antibody levels are important for disease diagnosis and assessing disease progression.

Enhancement of HBsAg detection in serum of patients with chronic liver disease following removal of circulating immune complexes

Patients with chronic liver disease and hepatocellular carcinoma may lack serological evidence of previous hepatitis B virus infection. The purpose of the present study was to test the hypothesis that circulating immune complexes may interfere with the detection of low levels of HBsAg in such patients. Sera from 190 patients were initially screened for the presence of circulating immune complexes. Patients belonged to three clinical categories: asymptomatic HBsAg carriers (50 patients), chronic liver disease (30 patients) and hepatocellular carcinoma (110 patients). Forty-one of the group of 190 patients (21%) were positive for circulating immune complexes. Sera from 21 patients were selected for further evaluation. The sera of 13 chronic liver disease or hepatocellular carcinoma patients (HBsAg negative, hepatitis B virus-DNA negative, with or without evidence of previous hepatitis B virus infection) and eight HBsAg positive carriers (four asymptomatic, three with chronic liver disease and one with hepatocellular carcinoma) were passed through a Clq affinity column (first column) to remove circulating immune complexes. Unbound material was then passed through a monoclonal IgG2a anti-HBs affinity column (second column). Unbound material (following both columns) contained free HBsAg, as determined by monocolonal radio-immunoassay, in eight patients in whom HBsAg had been undetectable in the original serum. Removal of circulating immune complexes from the serum of the three HBsAg positive patients with chronic liver disease also caused a significant increase in measurable circulating HBsAg compared with the original serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigen detection in immune complexes by a modified staphylococci binding assay and Western blot analysis

The combination of a modified Staphylococci binding assay for immune complexes and Western blot analysis is described for the isolation and detection of antigen in immune complexes from human sera. The strategy of the procedure is to preclear immune complexes from other serum components by sequential polyethylene glycol precipitation and incubation with insoluble protein A under conditions in which immune complexes are preferentially bound. Immune complexes are eluted from protein A in sodium dodecyl sulfate buffer and dissociated by acrylamide electrophoresis. Resolved proteins are then transblotted to nitrocellulose, and antigen is detected with specific antibody. Immune complexes were prepared in vitro with an antigen (keyhole limpet hemocyanin) that focuses well on electrophoresis and for which a potent immunologic probe (antibody) was available. In this system, antigen could be detected when immune complexes were present in sera in concentrations as low as 20 micrograms aggregated-IgG eq/ml, regardless of antigen-antibody ratio. We demonstrate the detection of horse globulin in immune complexes from a patient with acute serum sickness and hepatitis B virus antigen in complexes from a patient with vasculitis.