Coproantibodies in hepatitis A: detection by enzyme-linked immunosorbent assay and immune electron microscopy

Prolonged Gut Dysbiosis and Fecal Excretion of Hepatitis A Virus in Patients Infected with Human Immunodeficiency Virus

Hepatitis A virus (HAV) causes transient acute infection, and little is known of viral shedding via the duodenum and into the intestinal environment, including the gut microbiome, from the period of infection until after the recovery of symptoms. Therefore, in this study, we aimed to comprehensively observe the amount of virus excreted into the intestinal tract, the changes in the intestinal microbiome, and the level of inflammation during the healing process. We used blood and stool specimens from patients with human immunodeficiency virus who were infected with HAV during the HAV outbreak in Japan in 2018. Moreover, we observed changes in fecal HAV RNA and quantified the plasma cytokine level and gut microbiome by 16S rRNA analysis from clinical onset to at least 6 months after healing. HAV was detected from clinical onset up to a period of more than 150 days. Immediately after infection, many pro-inflammatory cytokines were elicited, and some cytokines showed different behaviors. The intestinal microbiome changed significantly after infection (dysbiosis), and the dysbiosis continued for a long time after healing. These observations suggest that the immunocompromised state is associated with prolonged viral shedding into the intestinal tract and delayed recovery of the intestinal environment.

Adaptive Immune Responses in Hepatitis A Virus and Hepatitis E Virus Infections

Both hepatitis A virus (HAV) and hepatitis E virus (HEV) cause self-limited infections in humans that are preventable by vaccination. Progress in characterizing adaptive immune responses against these enteric hepatitis viruses, and how they contribute to resolution of infection or liver injury, has therefore remained largely frozen for the past two decades. How HAV and HEV infections are so effectively controlled by B- and T-cell immunity, and why they do not have the same propensity to persist as HBV and HCV infections, cannot yet be adequately explained. The objective of this review is to summarize our understanding of the relationship between patterns of virus replication, adaptive immune responses, and acute liver injury in HAV and HEV infections. Gaps in knowledge, and recent studies that challenge long-held concepts of how antibodies and T cells contribute to control and pathogenesis of HAV and HEV infections, are highlighted.

Specific IgA Enhances the Transcytosis and Excretion of Hepatitis A Virus

Hepatitis A virus (HAV) replicates in the liver, and is excreted from the body in feces. However, the mechanisms of HAV transport from hepatocytes to the gastrointestinal tract are poorly understood, mainly due to lack of suitable in vitro models. Here, we use a polarized hepatic cell line and in vivo models to demonstrate vectorial transport of HAV from hepatocytes into bile via the apical cell membrane. Although this transport is specific for HAV, the rate of fecal excretion in inefficient, accounting for less than 1% of input virus from the bloodstream per hour. However, we also found that the rate of HAV excretion was enhanced in the presence of HAV-specific IgA. Using mice lacking the polymeric IgA receptor (pIgR^−/−), we show that a proportion of HAV:IgA complexes are transported via the pIgR demonstrating a role for specific antibody in pathogen excretion.

Innate and adaptive immune responses against picornaviruses and their counteractions: An overview

Picornaviruses, small positive-stranded RNA viruses, cause a wide range of diseases which is based on their differential tissue and cell type tropisms. This diversity is reflected by the immune responses, both innate and adaptive, induced after infection, and the subsequent interactions of the viruses with the immune system. The defense mechanisms of the host and the countermeasures of the virus significantly contribute to the pathogenesis of the infections. Important human pathogens are poliovirus, coxsackievirus, human rhinovirus and hepatitis A virus. These viruses are the best-studied members of the family, and in this review we want to present the major aspects of the reciprocal effects between the immune system and these viruses.

Laboratory diagnosis of hepatitis A

The diagnostic gold standard for hepatitis A is the detection of anti-hepatitis A virus (HAV) IgM antibodies and the determination of total anti-HAV by enzyme immunoassay. However, detection of HAV RNA can be useful in the diagnosis of patients without specific antibodies for hepatitis A and for the monitoring of infection. Studies using real-time PCR have demonstrated that HAV RNA can be detected not only in feces, but also in serum and saliva samples earlier than detection of antibodies, and that viremia may be present for a much longer period than the convalescent phase of hepatitis A. Alternative samples have been proposed for diagnosis, epidemiological studies, investigation of outbreaks and selection of persons receptive to vaccination. Understanding the events of clinical course that take place during the hepatitis A infection may lead to more effective diagnosis.

The role of immunoglobulin A in prolonged and relapsing hepatitis A virus infections

Hepatitis A virus (HAV) infections result in different courses of the disease, varying between normal, prolonged and relapsing. However, the reason for these heterogeneous clinical appearances is not understood. As HAV-anti-HAV IgA immunocomplexes (HAV-IgA) infect hepatocytes, IgA was postulated as a carrier supporting hepatotropic transport of HAV, and it was speculated that this carrier mechanism contributes to the various clinical outcomes. In this study, the IgA-carrier mechanism was investigated in a mouse model. We show that HAV-IgA immunocomplexes efficiently reached the liver not only in HAV-seronegative mice, but also, and this is in contrast to free-HAV particles, in immunized HAV-seropositive animals. This IgA-mediated transport of HAV to the liver in the presence of immunity depended on the stage of development of the immune response. We conclude that over a period of several weeks after infection, anti-HAV IgA is able to promote an enterohepatic cycling of HAV, resulting in continuous endogenous reinfections of the liver. Our experiments indicate that highly avid IgG antibodies, which are present at later times of the infection, can terminate the reinfections. However, the endogenous reinfections in the presence of a developing neutralizing immunity might contribute to prolonged as well as to relapsing courses of HAV infections. Furthermore, the results show that serum IgA may act as an infection protracting factor.

Diagnosis of hepatitis a virus infection: a molecular approach

Current serologic tests provide the foundation for diagnosis of hepatitis A and hepatitis A virus (HAV) infection. Recent advances in methods to identify and characterize nucleic acid markers of viral infections have provided the foundation for the field of molecular epidemiology and increased our knowledge of the molecular biology and epidemiology of HAV. Although HAV is primarily shed in feces, there is a strong viremic phase during infection which has allowed easy access to virus isolates and the use of molecular markers to determine their genetic relatedness. Molecular epidemiologic studies have provided new information on the types and extent of HAV infection and transmission in the United States. In addition, these new diagnostic methods have provided tools for the rapid detection of food-borne HAV transmission and identification of the potential source of the food contamination.

Diagnosis of hepatitis a virus infection: a molecular approach

Current serologic tests provide the foundation for diagnosis of hepatitis A and hepatitis A virus (HAV) infection. Recent advances in methods to identify and characterize nucleic acid markers of viral infections have provided the foundation for the field of molecular epidemiology and increased our knowledge of the molecular biology and epidemiology of HAV. Although HAV is primarily shed in feces, there is a strong viremic phase during infection which has allowed easy access to virus isolates and the use of molecular markers to determine their genetic relatedness. Molecular epidemiologic studies have provided new information on the types and extent of HAV infection and transmission in the United States. In addition, these new diagnostic methods have provided tools for the rapid detection of food-borne HAV transmission and identification of the potential source of the food contamination.

IgA-coated particles of Hepatitis A virus are translocalized antivectorially from the apical to the basolateral site of polarized epithelial cells via the polymeric immunoglobulin receptor

Although Hepatitis A virus (HAV) is transmitted by the faecal-oral route, its target for replication is the liver. Little is known of its interactions with cells of the gastrointestinal tract, and it is not known by which mechanisms HAV crosses the intestinal epithelium. In this study, it is shown that HAV associated with IgA is translocated from the apical to the basolateral compartment of polarized epithelial cells via the polymeric immunoglobulin receptor by IgA-mediated reverse transcytosis. The relevance of this mechanism, by which HAV-IgA complexes may overcome the intestinal barrier and contribute to infections of the liver, results from the fact that HAV-IgA complexes are infectious for hepatocytes and that significant amounts of intestinal HAV-IgA are present during acute infections, which are also partly transmitted. Besides supporting the primary infection, this mechanism may play a role in relapsing infections by establishing an enterohepatic cycle for HAV.

Evaluation of urine as a clinical specimen for diagnosis of hepatitis a

The present study pertains to the evaluation of urine as a specimen for detection of anti-hepatitis A virus (anti-HAV) antibodies. Immunoglobulin M (IgM), IgG, and IgA capture enzyme-linked immunosorbent assays for hepatitis A were performed on paired serum and urine specimens collected from hepatitis A patients (n = 92), healthy individuals (n = 100), non-A hepatitis patients (n = 70), and patients with nonhepatic diseases (n = 64, including 37 renal disease patients). Hepatitis A patients seropositive for anti-HAV IgM showed 95.65% uropositivity. No false-positive reactions were observed in control groups. The uropositivity of anti-HAV IgM persisted during the convalescent phase of the disease. Anti-HAV IgG uropositivity correlated well with corresponding seropositivity in all groups (P > 0.05 for each). No significant difference between the proportions of serum and urine positivity for anti-HAV IgA was noted (P > 0.05 for each). Using seroreactivity as a "gold standard," the sensitivity and specificity for anti-HAV IgM, anti-HAV IgG, and anti-HAV IgA tests with urine as a specimen were found to be 95.65 and 100%, 97.76 and 76.47%, and 92.23 and 88.18%, respectively. Urine appears to be comparable to serum for diagnosis of recent and past infection with hepatitis A.

Hepatitis A virus-specific immunoglobulin A mediates infection of hepatocytes with hepatitis A virus via the asialoglycoprotein receptor

The mechanisms underlying the hepatotropism of hepatitis A virus (HAV) and the relapsing courses of HAV infections are unknown. In this report, we show for a mouse hepatocyte model that HAV-specific immunoglobulin A (IgA) mediates infection of hepatocytes with HAV via the asialoglycoprotein receptor, which binds and internalizes IgA molecules. Proof of HAV infection was obtained by detection of HAV minus-strand RNA, which is indicative for virus replication, and quantification of infectious virions. We demonstrate that human hepatocytes also ingest HAV-anti-HAV IgA complexes by the same mechanism, resulting in infection of the cells, by using the HepG2 cell line and primary hepatocytes. The relevance of this surrogate receptor mechanism in HAV pathogenesis lies in the fact that HAV, IgA, and antigen-IgA complexes use the same pathway within the organism, leading from the gastrointestinal tract to the liver via blood and back to the gastrointestinal tract via bile fluid. Therefore, HAV-specific IgA antibodies produced by gastrointestinal mucosa-associated lymphoid tissue may serve as carrier and targeting molecules, enabling and supporting HAV infection of IgA receptor-positive hepatocytes and, in the case of relapsing courses, allowing reinfection of the liver in the presence of otherwise neutralizing antibodies, resulting in exacerbation of liver disease.

VP7 and VP4 genotyping of human group A rotavirus in Buenos Aires, Argentina

Specific and sensitive tests for the detection and typing of group A rotavirus strains are needed for a more comprehensive knowledge of the epidemiology of rotaviral infection. In this study 500 stool specimens taken from 1996 to 1998 from children with acute diarrhea in Buenos Aires were examined. Group A rotavirus was unequivocally demonstrated in 62% of the samples tested by enzyme-linked immunosorbent assay (ELISA) for detection of VP6 antigen, polyacrylamide gel electrophoresis of double-stranded RNA, and reverse transcription-PCR (RT-PCR) for amplification of the VP7:G (1, 062 bp) and VP4:P (876 bp) genes. Only five positive specimens were found by RT-PCR but not by ELISA. G and P typing was carried out by nested amplification of variable sequences of the VP7 and the VP4 genes with six G- and five P-type-specific primers (multiplex PCR). Results obtained by this method showed the prevalence of the following G and P types: G1, 39%; G2, 43%; G4, 4%; P[8], 16%; P[4], 71%. Unexpectedly, the G-P type combination most frequently found was G2P[4] (43%) rather than G1P[8] (12%), which is the most commonly found worldwide. Unusual strains of the type G1P[4] accounted for 14% of the total, while mixed infections with more than one type were found in 10% of the samples. Detection of fecal rotavirus-specific immunoglobulin M (IgM) and IgA antibodies in consecutive samples of two patients taken at daily intervals demonstrated that high levels of IgM and IgA antibodies were detected on day 1 after the onset of disease and that the samples remained positive for about 10 days, after which virus shedding was no longer observed. Multiplex PCR offers a sensitive and specific alternative to determine the prevalence of group A rotavirus G and P types and to identify the emergence of uncommon strains, whereas detection of fecal IgM and IgA antibodies represents a useful supplement to virus detection for the diagnosis of current or recently acquired infections.

Technical report: results of immunological tests on faecal extracts are likely to be extremely misleading

Clinical investigation of gut immunity is difficult because of the need to study intestinal tissues or secretions directly. Others have reported that immunoglobulins, antibodies and cytokines can be detected in saline extracts of faeces. We have assessed the validity of this approach by measuring immunoglobulins, albumin, alpha 1-antitrypsin and isotype-specific antibodies in matched samples of faeces and whole gut lavage fluid. Results were compared as estimated output per day, and by using haemoglobin as a common reference substance. Samples were obtained from 10 patients with active inflammatory bowel disease and 10 with other benign GI diseases. For immunoglobulins, albumin and antibodies, the amount detected in faeces varied from < 0.01% to 35.5% (based on estimated daily output) and < 0.01% to 18.5% (based on haemoglobin) of the amount known to be produced in the gut from results of assays on whole gut lavage fluid (WGLF); there were significantly higher rates of recovery in faecal specimens from patients with active gut inflammation than from other patients. Detection rates and titres of specific antibody in faeces were even lower than those for immunoreactive IgA. These data indicate that immunological tests on saline extracts of faeces do not represent the true status of the gut humoral immune system, and such studies should be strongly discouraged.

Immunoreactivity of human and rabbit antisera to hepatitis A virus

Rabbit antibodies produced by immunization with complete hepatitis A virions (HAV) recognized all the viral structural proteins and neutralized HAV infectivity in cell culture. Rabbit antibodies to chromatographically purified individual viral proteins and to synthetic peptides representing epitopes on the structural viral protein VP1 neither recognized whole virus nor neutralized infectivity, indicating that native epitopes on the virus surface are necessary for virus recognition and neutralization. Human anti-HAV-positive sera of the acute and convalescent phase of disease recognized and neutralized viral particles. Analysis of the immunoreactivity of these human sera in immunoblot showed that the IgM antibody preferentially recognizes the structural viral proteins VP0 and VP3 of HAV, whereas IgA and IgG antibodies reacted more strongly with VP1.

Towards a hepatitis A vaccine. A review

Hepatitis A is an acute inflammation of the liver caused by a virus (HAV) whose morphology and physical characteristics resemble members of the enterovirus group. The disease, which is characterized by fever, malaise, anorexia, nausea, abdominal discomfort and jaundice has an average incubation period of 28–30 days and is spread from person to person by the faecal-oral route. Common-vehicle outbreaks have been reported following contamination of food or water and epidemics may occur in closed communities (institutions, day-care centres) or in the general community when there is a breakdown of environmental sanitation. Many infections, especially in children, are subclinical; the case fatility rate for patients requiring hospitalization is low and long-term sequelae are unknown.

Hepatitis A-virus in cell culture. V. Neutralizing antibodies against hepatitis A-virus

A test system for the detection of neutralizing antibodies against hepatitis A-virus (anti-HAV-Nt) is presented. The anti-HAV-Nt assay is performed with Frhk-4/R cells and the hepatitis A virus (HAV) strain GBM/Frhk-4/R which has been adapted to these cells. Non-neutralized HAV is demonstrated 14 days after infection of Frhk-4/R cells using a radio-immunoassay for detecting newly grown HAV. The influence of differing amounts of HAV on the anti-HAV-Nt titre and the effect of variations in incubation time of virus-serum mixtures are described. The time course of anti-HAV-Nt is shown in sera from a hepatitis-A patient which were taken at different stages of the disease. Anti-HAV-Nt is compared with anti-HAV and anti-HAV-IgM. It is shown that anti-HAV-Nt correlates closely with anti-HAV and separated anti-HAV-IgG, but only slightly with anti-HAV-IgM. The test system presented makes possible the demonstration of neutralizing antibodies against HAV in gamma-globulin preparations and during vaccination studies.

The detection and measurement of coproantibodies to Nippostrongylus brasiliensis in rats following a primary infection

Investigations were initiated to study the possible detection and measurement of coproantibodies in animals infected with a gastrointestinal nematode parasite. Faecal extracts, extracts of small intestinal mucosa and sera of rats infected with intestinal nematode Nippostrongylus brasiliensis were examined for total IgA, IgM and IgG levels and haemagglutinating and precipitating antibodies specific to parasite antigens over a 30-day-period following infection. It was found that in both faecal and mucosal extracts immunoglobulin concentrations increased after a primary infection. In faecal extracts there was a seven-fold increase of IgA, a three to six-fold increase of IgG and about a fifty-fold increase of IgM. Haemagglutinins in faecal extracts detected by adult worm excretory-secretory (ES) products and adult worm and infective larvae somatic extracts were observed from 3 days after infection (DAI). Haemagglutinins detected by ES products reached their highest titres on 11-12 DAI while those reacting with adult worm somatic extracts showed the highest level between 15 and 19 DAI. A similar pattern of response was found in the antibody levels of the intestinal mucosa. Haemagglutinins detected in faeces during the first 12 DAI reacted with the same antigens as antibodies present in the sera at that time but coproantibodies from 18, 24 and 30 DAI were different from those circulating in sera at that stage of the infection. The results suggest that measurement of coproantibody levels may provide a convenient and useful index of local immune responses to gastrointestinal helminths.

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: virologic, clinical, and epidemiologic studies

The last decade has borne witness to accelerated expansion of our understanding of hepatitis A virus. The agent of type A hepatitis is an RNA virus with a mean diameter of 27 nm. and biochemical-biophysical properties of an enterovirus. A variety of sensitive specific serologic techniques have been developed with which to identify hepatitis A virus and antibody, and both chimpanzees and marmosets have been studied extensively as experimental animal models. As a result of these studies, in vitro cultivation of hepatitis A virus has finally been accomplished, and a commercial radioimmunoassay for IgM antibody to hepatitis A virus has been developed for the rapid diagnosis of hepatitis A virus infection during acute illness. Clinically the illness caused by hepatitis A virus is relatively mild, often subclinical, and of limited duration and does not progress to chronic liver disease. This relative clinical benignity is reflected, according to preliminary histologic observations, in the sparing of the centrozonal area of the liver lobule. Rarely, however, hepatitis A virus can cause fulminant hepatitis. Type A hepatitis is transmitted almost exclusively by the fecal-oral route, and its spread is enhanced by epidemiologic settings favoring dissemination of enteric infections. Hepatitis A virus does not contribute to transfusion associated or other types of percutaneously transmitted hepatitis. Exposure to the virus increases as a function of age and decreasing socioeconomic class, but the incidence of hepatitis A virus infection in urbanized societies is decreasing. There is no evidence for the existence of chronic hepatitis A virus carriage; natural perpetuation of hepatitis A virus in urban communities appears to depend on a reservoir of nonepidemic, clinically inapparent cases. Until a vaccine, now being developed, becomes available, prevention of hepatitis A virus infection will continue to depend on maintenance of high standards of environmental and personal hygiene and on timely administration of immune serum globulin. Such prophylaxis may confer long lasting passive-active immunity but more frequently prevents infection entirely.