Innate immune recognition and modulation in hepatitis D virus infection.

Hepatitis D virus (HDV) is a global health threat with more than 15 million humans affected. Current treatment options are largely unsatisfactory leaving chronically infected humans at high risk to develop liver cirrhosis and hepatocellular carcinoma. HDV is the only human satellite virus known. It encodes only two proteins, and requires Hepatitis B virus (HBV) envelope protein expression for productive virion release and spread of the infection. How HDV could evolve and why HBV was selected as a helper virus remains unknown. Since the discovery of Na+-taurocholate co-transporting polypeptide as the essential uptake receptor for HBV and HDV, we are beginning to understand the interactions of HDV and the immune system. While HBV is mostly regarded a stealth virus, that escapes innate immune recognition, HBV-HDV coinfection is characterized by a strong innate immune response. Cytoplasmic RNA sensor melanoma differentiation antigen 5 has been reported to recognize HDV RNA replication and activate innate immunity. Innate immunity, however, seems not to impair HDV replication while it inhibits HBV. In this review, we describe what is known up-to-date about the interplay between HBV as a helper and HDV's immune evasion strategy and identify where additional research is required.

Cross-protection: a century of mystery.

Cross-protection is a phenomenon in which infection of a plant with a mild virus or viroid strain protects it from disease resulting from a subsequent encounter with a severe strain of the same virus or viroid. In this chapter, we review the history of cross-protection with regard to the development of ideas concerning its likely mechanisms, including RNA silencing and exclusion, and its influence on the early development of genetically engineered virus resistance. We also examine examples of the practical use of cross-protection in averting crop losses due to viruses, as well as the use of satellite RNAs to ameliorate the impact of virus-induced diseases. We also discuss the potential of cross-protection to contribute in future to the maintenance of crop health in the face of emerging virus diseases and related threats to agricultural production.

Prevalence of serum IgG and neutralizing factors against adeno-associated virus (AAV) types 1, 2, 5, 6, 8, and 9 in the healthy population: implications for gene therapy using AAV vectors.

Adeno-associated viruses (AAVs) are small, nonenveloped single-stranded DNA viruses that require helper viruses to facilitate efficient replication. Despite the presence of humoral responses to the wild-type AAV in humans, AAV remains one of the most promising candidates for therapeutic gene transfer to treat many genetic and acquired diseases. Characterization of the IgG subclass responses to AAV and study of the prevalence of both IgG and neutralizing factors to AAV types 1, 2, 5, 6, 8, and 9 in the human population are of importance for the development of new strategies to overcome these immune responses. Natural exposure to AAV types 1, 2, 5, 6, 8, and 9 can result in the production of antibodies from all four IgG subclasses, with a predominant IgG1 response and low IgG2, IgG3, and IgG4 responses. Prevalences of anti-AAV1 and -AAV2 total IgG determined by enzyme-linked immunosorbent assay were higher (67 and 72%) than those of anti-AAV5 (40%), anti-AAV6 (46%), anti-AAV8 (38%), and anti-AAV9 (47%). Furthermore, data showed that cross-reactions are important. The two highest neutralizing factor seroprevalences were observed for AAV2 (59%) and AAV1 (50.5%) and the lowest were observed for AAV8 (19%) and AAV5 (3.2%). Vectors based on AAV5, AAV8, and AAV9 may have an advantage for gene therapy in humans. Furthermore, among individuals seropositive for AAV5, AAV8, and AAV9, about 70-100% present low titers. Better characterization of the preexisting humoral responses to the AAV capsid and cross-reactivity will allow development of new strategies to circumvent AAV acquired immune responses.

Immunochemical reactivity of simian sarcoma virus polypeptides isolated by preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis.

The polypeptides associated with a zonal centrifugation purified simian sarcoma virus propagated in lymphoblastoid NC-37 cells were isolated by preparative polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS) using a procedure designed to minimize the loss of immunochemical reactivity. The proteins p10, p15, p28, p36, p44, p75, and p86 were obtained in large yield and high degree of homogeneity. The electrophoretically purified p28 was analyzed by competition radioimmunoassay using antiserum to a pore exclusion and ion exchange purified simian sarcoma virus p28. Complete competition was observed with extracts of simian sarcoma virus infected cells. No competition was observed with uninfected or unrelated, infected cell extracts. The antigen-antibody affinity as measured by the slope of the competition curve using antiserum to p28 and 125I-labeled and electrophoretically purified p28 was the same as that for the p28 released from sonication-disrupted simian sarcoma virus. The data indicates that preparative purifications by polyacrylamide gel electrophoresis in the presence of SDS may be generally applicable for the isolation of proteins with essentially the same immunospecificities and affinity for a specific antiserum as proteins isolated by procedures that avoid the use of SDS and electrophoresis.

Neutralizing antibodies to CELO and avian adenovirus-associated viruses in the albumen of chicken eggs.

Neutralizing antibodies to CELO virus and to avian adenovirus-associated virus (A-AV) were detected in the albumen of eggs from four hens inoculated with these viruses. The antibody concentrations of serum, yolk, and albumen were determined before inoculation and at various times postinoculation (PI) by enzyme-linked immunosorbent assay (ELISA) and virus-neutralization (VN) tests. The antibody concentration in albumen was 0.3% to 1.0% of that detected in serum and yolk. Uninoculated hens showed no detectable antibody in serum, yolk, or albumen. It is suggested that the presence of antibody in the egg albumen may play a role in egg-transmission of viruses.

Egg transmission of avian adenovirus-associated virus and CELO virus during a naturally occurring infection.

Both avian adenovirus-associated virus (A-AV) and CELO virus were isolated from the embryonating eggs of 25-week-old black sex-linked hens during a naturally occurring infection. In the first 7 days of egg collection, A-AV was isolated from 10 of 43 (23.2%) embryonating eggs, and CELO virus was isolated from 8 of 43 (18.6%) embryonating eggs. Both viruses were isolated from six eggs. In the next 16 days of egg collection, A-AV and CELO virus were coisolated from 1 of 127 (0.8%) eggs; all other samples were negative for both viruses. All six hens transmitting A-AV to eggs and 5 of 6 hens transmitting CELO virus showed seroconversions (fourfold increase in antibody concentrations). Viruses were not isolated from eggs after the hens showed a fourfold increase in antibody concentrations.

Suppression of in vitro antibody response by spleen cells of mice infected with Friend-associated lymphatic leukemia virus.

The ability of spleen cells of mice infected with oncornaviruses to depress the in vitro antibody responsiveness of normal lymphoid cells was exploited in an attempt to clarify the role played by the lymphatic leukemia virus (LLV) component in the immunodepressive properties of the Friend leukemia complex. Spleen cells of mice infected with LLV or, for comparison, with the entire complex were added to cultures of sheep erythrocyte-primed uninfected spleen cells, and the antibody-forming cells produced by the latter, after antigen restimulation, were assayed. The addition within 2 days from culture initiation of low numbers of cells infected with either virus preparation suppressed all stages of the response affecting the production of both immunoglobulin M and immunoglobulin G antibody. The activity of infected cells resisted doses of ultraviolet radiation which inhibit cell multiplication but was abolished by disrupting the cells and was prevented by the presence of anti-LLV antibodies. The LLV-infected spleen cells responsible for suppression were not removed by treatments which selectively remove or kill macrophages and exhibited surface properties of B lymphocytes. These results were interpreted as indicating that the effect is due to virus (or viral products) released by B cells. The suppressing cells in the spleens of mice in the early days of Friend leukemia complex infection presented superimposable properties, supporting the concept that their activity is also due to the LLV they release in large quantities. However, in later stages of infection, the spleens of Friend leukemia complex-infected mice also contained non-B-suppressing cells possibly derived from the proliferation of nonlymphoid LLV-producing cells caused by the neoplastic process.

Isolation and identification of a bovine adenovirus type 3 with an adenovirus-associated virus.

A bovine adenovirus with agglutinating activity was isolated from feedlot calves and classified as serotype 3. The agglutinating activity was shown to be the property of an adenovirus-associated virus (AAV). The AAV was isolated from the bovine adenovirus by isopycnic centrifugation in CsCl; the AAV had a density of 1.4 g/cm2. This AAV is serologically related to bovine AAV-TR-15, but is distinct from bovine parvovirus-1 and primate AAV types 1 to 4, using counterimmunoelectrophoresis and hemagglutination-inhibition.

Serological response of chickens exposed to a type 1 avian adenovirus alone or in combination with the adeno-associated virus.

The avian adenoviruses (AV) are common infectious agents of poultry and other avian species throughout the world (1,4,8). Limited observations suggest that the adeno-associated virus (A-AV) coinfects many of the chickens that carry AV (8). The presence and persistence of these infections in a flock is often determined by serological methods. In the current study, the immune response of chickens to type 1 AV alone and to a dual exposure, AV plus A-AV, was followed over a 12-week period with a variety of serological tests. The study also determined the duration of the viral infections.

Complementation of adeno-associated satellite virus (AAV) by temperature-sensitive mutants of adenovirus type 31.

Temperature-sensitive (ts) matants of human adenovirus type 31 were able to complement adeno-associated satellite virus (AAV) antigen production in both HEK and KB cells at both permissive and non-permissive temperatures. However, mutant ts 94, an adenovirus 31 mutant which produces apparently normal amounts of structural protein and DNA but is defective in maturation, was significantly inhibited in its ability to potentiate AAV infectivity at the non-permissive temperature. Normal AAV DNA and adenovirus DNA were isolated from co-infections with AAV and mutant ts 94 at the non-permissive temperature. We suggest that an adenovirus-coded maturation function common to both adenovirus and AAV maturation is defective in the ts 94 system.

[Antigens of adeno-associated viruses in children dying from acute respiratory disease]. / Antigeny adenoassotsiirovannykh virusov u detei, umershikh ot ostrogo respiratornogo zabolevaniia.

Infection with adeno-associated viruses (AAV) early in life and extensive dissemination of these viruses in infants were discovered by detection of AAV antigen by the fluorescent antibody procedure in autopsy materials from infants dying of acute respiratory viral diseases. AAV antigens were found in cells from various organs of infants aged 2,5, 7, 9 days and older. In each individual case AAV of the same serological type was found in different organs. In 4-months-old twins AAV antigens of the same serotypes, 1 and 4, were found in the trachea, lungs, liver, kidney, brains. Out of 21 infants dying of adenovirus infection, 20 had AAV antigens the distribution of which in cells of various organs was analogous to that of the adenovirus antigen, with a few exceptions. Three infants had no adenovirus infection and no AAV antigne. In the other 6 infants no adenovirus antigen but AAV antigens were found. In the latter cases herpes virus infection is not excluded. Possible modes of transmission of AAV infection are discussed.

Antibodies to adeno-associated satellite virus and herpes simplex in sera from cancer patients and normal adults.

The ecologic aspects of the distribution of adeno-associated satellite virus (ASV) in the human population are of great interest because of its unconditional defectiveness and dependence on adenovirus for full and herpesvirus for partial complementation. Adenoviruses and herpesviruses are extremely common and persistent infections in man. We have developed immunofluorescent procedures for detecting the presence of satellite virus antibodies in human sera. The percentage of sera with antibodies to the ASV 2-3 complex was significantly higher in the normal group than in the cancer patients whereas there were no significant differences in herpes antibodies between the groups. The low incidence of satellite antibodies was particularly striking in patients with genital malignancies. The role of ASV's in human disease is not known. Their role in possible abrogation of oncogenesis mediated through adenoviruses or herpesviruses is worthy of further investigation.

Isolation and characterization of adeno-associated viruses from bovine adenovirus types 1 and 2.

Hemagglutinating DNA viruses of 20 nm diameter were isolated from bovine adenovirus types 1 and 2. The isolates were heat stable, chloroform resistant, and defective. Their densities were 1.38 to 1.39 g/cm3, and they were found to be serologically identical to the bovine adeno-associated virus strain X7. A partial antigenic relationship was found between these and the canine adeno-associated virus.