Natural and experimentally induced antibodies to defined mammalian type-C virus proteins in primates

Retroelements and the human genome: new perspectives on an old relation

Retroelements constitute a large portion of our genomes. One class of these elements, the human endogenous retroviruses (HERVs), is comprised of remnants of ancient exogenous retroviruses that have gained access to the germ line. After integration, most proviruses have been the subject of numerous amplifications and have suffered extensive deletions and mutations. Nevertheless, HERV-derived transcripts and proteins have been detected in healthy and diseased human tissues, and HERV-K, the youngest, most conserved family, is able to form virus-like particles. Although it is generally accepted that the integration of retroelements can cause significant harm by disrupting or disregulating essential genes, the role of HERV expression in the etiology of malignancies and autoimmune and neurologic diseases remains controversial. In recent years, striking evidence has accumulated indicating that some proviral sequences and HERV proteins might even serve the needs of the host and are therefore under positive selection. The remarkable progress in the analysis of host genomes has brought to light the significant impact of HERVs and other retroelements on genetic variation, genome evolution, and gene regulation.

Characterization of the antibody response specific for the human endogenous retrovirus HTDV/HERV-K

Differentiated human teratocarcinoma cell lines produce the human teratocarcinoma-derived virus (HTDV) particles encoded by the human endogenous retrovirus sequence HERV-K. We screened almost 2,000 human sera for antibodies against this endogenous human retrovirus, HTDV/HERV-K. Specificity of the immunofluorescence reactions using particle producing teratocarcinoma cells was confirmed by immunoelectron microscopy of ultrathin frozen sections. Immunoblot analyses using lysates of HTDV-producing cells revealed a 80-kDa HERV-K Gag precursor and a 90-kDa putative viral Env protein after incubation with positive sera. No processed Gag protein could be observed. Virus-specific bands were not detected in lysates of nonproducing cells. High antibody titers were found in about 60% of male patients with germ cell tumors. Antibody reactivity declined after tumor removal. In healthy blood donors, anti-HTDV reactivity was found only at low titers in a small percentage (3.9%) of individuals. A slightly elevated but statistically significant percentage of HTDV positivity was also observed for sera of pregnant women, whereas human immunodeficiency virus-positive individuals exhibited no peculiarity compared to normal blood donors. Our results provide evidence that HTDV particles are expressed in vivo and that the immune reaction against HTDV/HERV-K is specific for defined viral proteins.

Selective antibody reactivity with peptides from human endogenous retroviruses and nonviral poly(amino acids) in patients with systemic lupus erythematosus

OBJECTIVE

To investigate antibody responses to a broad panel of peptides derived from human endogenous retroviruses (HERVs) among unselected patients with systemic lupus erythematosus (SLE).

METHODS

In sera obtained from 69 patients with SLE and healthy blood donors, immunoassay was used to measure levels of antibody against synthetic peptides derived from HERVs, exogenous retroviruses, and nonviral poly(amino acids).

RESULTS

Measurement by immunoassay revealed increased frequencies of antiretroviral antibodies against 2 peptides derived from the env gene of the type C-like class, which includes ERV-9 and HERV-H, and against 2 peptides from the gag region of human T lymphotropic virus type I-related endogenous sequence 1, in patients with SLE. Antibodies to 2 nonviral peptides, polyhistidine and polyproline, were also overrepresented in patient sera. In 1 patient, longitudinal data obtained over a period of 12 years indicated that the concentrations of certain antiretroviral antibodies varied according to disease activity.

CONCLUSION

Reactivity to certain type C HERV-derived antigens was found among patients with SLE. This reactivity could be explained by increased exposure to cross-reactive epitopes from essentially complete type C HERVs.

Increased antiretroviral antibody reactivity in sera from a defined population of patients with systemic lupus erythematosus. Correlation with autoantibodies and clinical manifestations

OBJECTIVE

The implied role of retroviruses in the pathogenesis of murine systemic lupus erythematosus (SLE) led us to study antiretroviral antibodies in a population-based SLE cohort.

METHODS

Immunoassays using whole virus and synthetic peptides were performed on sera from 72 patients with SLE and 88 control subjects.

RESULTS

Reactions with whole baboon endogenous virus occurred more frequently in patients with SLE, and correlated with the presence of anti-RNP and anti-Sm. Some retroviral env and gag peptides, several of which were similar to U1 small nuclear RNP, reacted more strongly in patients with SLE, and their presence was correlated with discoid rash, hematologic disorder, and other symptoms.

CONCLUSION

These results provide circumstantial evidence for involvement of retroviruses in the pathogenesis of human SLE; further studies should be carried out using other techniques for measurement of retroviral expression.

Human T-cell lymphotropic virus type III: immunologic characterization and primary structure analysis of the major internal protein, p24

The major internal structural protein of human T-cell lymphotropic virus type III (HTLV-III), a virus etiologically implicated in acquired immunodeficiency syndrome (AIDS), was purified to homogeneity. This 24,000-molecular-weight protein (p24) was shown to lack immunologic cross-reacting antigenic determinants shared by other known retroviruses, including HTLV-I and HTLV-II, with the exception of equine infectious anemia virus (EIAV). A broadly reactive competition immunoassay was developed in which antiserum to EIAV was used to precipitate 125I-labeled HTLV-III p24. Although the major structural proteins of HTLV-III and EIAV competed in this assay, other type B, C, and D retroviral proteins lacked detectable reactivity. Thus, HTLV-III is more related to EIAV than to any other retroviruses. That the HTLV-III isolate is very distinct from HTLV-I and HTLV-II was further confirmed by the amino acid compositions of the major internal antigens of all three isolates. Moreover, comparison of the amino-terminal amino acid sequence of HTLV-III p24 with analogous sequences for HTLV-I and HTLV-II p24 showed that these proteins do not share significant sequence homology. In an attempt to evaluate immune response in individuals exposed to HTLV-III, sera from AIDS and lymphadenopathy syndrome patients as well as from clinically normal blood donor controls were tested for antibodies to HTLV-III p24. The results showed that sera from 93% of lymphadenopathy syndrome patients and 73% of AIDS patients exhibited high-titered antibodies to HTLV-III p24. In contrast, none of the normal control sera showed detectable reactivity to HTLV-III p24.

Humans have antibodies capable of recognizing oncoviral glycoproteins: demonstration that these antibodies are formed in response to cellular modification of glycoproteins rather than as consequence of exposure to virus

There is controversy in the literature concerning the presence in humans of antibodies directed against the envelope glycoproteins of known oncoviruses. In the present report, we show that antibodies capable of precipitating a wide variety of oncoviral glycoproteins can be demonstrated under certain assay conditions. Substances as diverse as normal components of serum, extracts of bacteria, and even nonprotein molecules such as glycogen also shared the oncoviral glycoprotein determinants recognized by normal human sera. It was found that immunoprecipitation of a given viral glycoprotein by human sera was entirely dependent upon the cell in which the virus was grown. Human sera specifically did not recognize glycoproteins purified from oncoviruses grown in human or higher primate cells. These findings not only demonstrate that the antibodies were directed against cellular rather than the virus-coded antigenic determinants but also exclude the possibility that this immune response was elicited as a consequence of oncovirus exposure.

Specificity of human antibodies to oncovirus glycoproteins: recognition of antigen by natural antibodies directed against carbohydrate structures

Antibodies in human sera from healthy individuals were shown to be reactive with highly purified 70,000-dalton envelope glycoprotein (gp70) of the simian sarcoma virus-simian sarcoma-associated virus (SSV-SSAV) complex in radioimmunoprecipitation assays under certain conditions. The specificity of the reaction was analyzed in absorption tests with normal human serum proteins, assays of viral gp70 antigenicity after exposure to exo- and endoglycosidases or trypsin, and carbohydrate hapten inhibition studies. On the basis of the results obtained in these experiments we have concluded that immune recognition of SSV-SSAV gp70 can be mediated by naturally occurring heterophil antibodies in human sera that are reactive by virtue of binding to the carbohydrate moiety of the viral gp70 molecules. The results are consistent with the idea that the antibodies in question are elicited as a result of exposure to many natural substances possessing widely crossreacting antigens and are not a result of widespread infection of man with replication-competent oncoviruses.

Viruses and lymphocytes in rheumatoid arthritis. II. Examination of lymphocytes and sera from patients with rheumatoid arthritis for evidence of retrovirus infection

The possible involvement of retroviruses in the aetiology of rheumatoid arthritis (RA) was investigated. Retrovirus antigens were not expressed on rheumatoid synovial and peripheral blood lymphocytes as judged by membrane immunofluorescence, radioimmunoassay, and complement-mediated cytotoxicity. The specific antiretroviral (anti-RD-144 and anti-SSAV) sera used in this study were produced in rabbits immunised with viral antigens grown in a homologous system (rabbit cells and medium supplemented with normal rabbit serum), avoiding non-specific immunofluorescence previously detected with donated antiretroviral sera. Immune complexes lodged in the rheumatoid synovial membranes did not contain, and other cells within the membranes did not express, retroviral antigens. Antibodies cross-reacting with primate retrovirus antigens were sought in sera from patients with 'autoimmune' diseases by means of solid phase radioimmunoassay. There were no retrovirus antibodies in the 3 groups of patients studied, that is, those with rheumatoid arthritis, systemic lupus erythematosus, and with non-RA conditions. Absorption of rheumatoid factor did not alter this conclusion. These results give little support to the hypothesis that activation of endogenous human retroviruses or an infection with horizontally transmitted retroviruses is associated with the rheumatoid process.

Antigenic characterization of a new gibbon ape leukemia virus isolate: seroepidemiologic assessment of an outbreak of gibbon leukemia

A type-C virus recently isolated from a leukemic gibbon in a colony located on Hall's Island, Bermuda, was characterized with respect to the antigenic properties of its gag and env gene-coded proteins. This virus, designated GaLV-H, was found to be closely related immunologically to type-C viruses previously isolated from gibbons (GaLV-SF, GaLV-SEATO, GaLV-Br) and from woolly monkey (SSAV). However, GaLV-H was readily differentiated from these isolates in a radioimmunoassay for its env gene product, gp70. Seroepidemiology established that GaLV-H was horizontally transmitted among gibbons within the colony. There was no evidence of exposure leading to an immune response to the virus or viral antigenemia in humans working in association with these animals.

Immunologic approaches toward detection of type C viral expression in man

Type C RNA viruses have been isolated from a large number of mammalian species. These agents may be horizontally transmitted as infectious cancer-inducing agents, or vertically transmitted from one generation to the next, often in an unexpressed form, within the host genome. To date, the translational products of three viral genes have been identified. With purified virus-coded proteins as probes, sensitive and highly specific radioimmunologic assays have been developed for the detection of antibodies and antigens related to the known type C viruses. These techniques have proved valuable in sero-epidemiologic studies of the horizontally transmitted oncogenic viruses of cats, cattle, and gibbons, and have been used to detect translational products of endogenous viruses in tissues of species from which complete virus has yet to be isolated. This review describes the application of radioimmunoassays in the search for immunologic evidence of type C virus expression in man.

Radioimmunoassay for the major structural protein of Mason-Pfizer monkey virus: Attempts to detect the presence of antigen or antibody in humans

The 25,000 dalton protein of Mason-Pfizer monkey virus (MPMV) was isolated by gel filtration chromatography. In agreement with results from other laboratories, antisera to type-C and the non-type-C bovine leukemia and equine infectious anemia viruses did not precipitate 125I-labelled MPMV p25. In addition, these viruses did not cross-react in a competition radioimmunoassay for MPMV p25. Twenty-one human tissues (15 breast carcinomas, 2 normal breasts, 3 acute myelogenous leukemias and 1 sarcoma) were fractionated by detergent solubilization, ammonium sulfate precipitation, and DE-52 anion exchange chromatography. These methods were shown to be highly effective for purification of MPMV p25. Under assay conditions which minimized incubation damage to the 125I-MPMV p25, all tissues failed to react in the competition radioimmunoassay (RIAT). Two hundred and two human sera or plasma specimens, including those from patients with breast cancer and 33 age-matched controls, from 50 patients with hematologic malignancies, from 12 patients with amyotrophic lateral sclerosis, and from 14 patients with systemic lupus erythematosis, were examined for antibodies to MPMV p25. With the exception of two multiple myeloma plasma which produced artifactual false positive reactions based on hypergammaglobulinemia, a known complication of salt precipitation radioimmunoassays, the remainder of the specimens were negative for evidence of MPMV p25 antibodies.

FeLV epidemiology in Los Angeles cats: Appraisal of detection methods

We investigated the reliability of the fixed cell indirect fluorescent antibody (IFA) peripheral blood smear test as an index of systemic infection with FeLV. Positive results with this test were found to correlate well with detectable FeLV p30 antigen in bone-marrow smears by IFA, in serum and tissue by competition immunoassays, and with type-C particles in bone marrow or spleen by electron microscopy. Most cats with lymphoma, anemia or infectious peritonitis were positive for FeLV and showed a poor or absent antibody response to FeLV p30, gp70, and FOCMA antigens. Most older cats with lymphoma, carcinoma, or sarcoma were negative for FeLV expression and also lacked these FeLV-related antibodies. Detectable immunologic response to FeLV p30 and gp70 proteins and a high-titered FOCMA antibody response were generally restricted to certain healthy cats exposed to FeLV. Antibody to endogenous RD-114 viral p30 and gp70 was not detected in any of a large number of feline sera tested. The prevalence of FeLV-related diseases and immunologic responses to FeLV in healthy cats was directly correlated with the degree of FeLV exposure. By using the IFA blood smear and FOCMA antibody tests one can monitor the horizontal spread of FeLV in multi-cat household and accurately predict the FeLV disease susceptibilty or resistance of individual cats in each environments.

Leukemia following Reye's syndrome treated with exchange transfusions: search for type-C viral infection

A 5-year-old child developed acute lymphoblastic leukemia during convalescence from an episode of Reye's syndrome that was treated with multiple exchange transfusions. Routine laboratory, histology, and viral serology were unable to establish a common etiology for the 2 illnesses. Cultural and immunologic methods to search for evidence of infection with type-C viruses or viral genes in lymphoblasts from the buffy coat and bone marrow failed to reveal these agents. Although no common infectious etiology was defined for the close temporal occurrence of 2 rare diseases, the possibility of an iatrogenically induced malignancy was considered.

Humoral immune responses of cats to mammalian type-C virus p30s

Natural and experimental cat sera were tested in radioimmune precipitation assays vs purified p30s from FeLV, RD114 and MuLV. Antibodies with specificity for FeLV p30 comparable to hyperimmune sera from heterologous species but of low titer were found in a high percentage of normal cats from households with a high incidence of FeLV and neoplasia. Sera from cats with neoplasms were generally negative. Cats immunized with FeLV gave low-level immune response, also of the same general specificity as heterologous hyperimmune sera. Cat sera do not normally show antibody to RD114 p30 although two immunized weanling cats produced low titered but highly specific p30 antibody. Thus, for both classes of feline type-C virus p30s, there is an evident capability of the cat to mount an immune response to natural or experimental exposure to the respective proteins. The magnitude of the response is between 100 and 1,000 fold below that seen in heterologous species. In contrast, cats immunized with MuLV p30 gave immune responses comparable to those seen in guinea-pigs, rabbits and goats. Several very old cats with carcinoma had antibody which preferentially precipitated MuVL p30. A competition assay using one such serum and labelled MuVL p30 was inhibited by FeVL, RD114, and MuLV p30s. This indicates that the assay is "interspecies" in nature. Among the possible explanations of this reaction category is that it represents antibody to the p30 of an as yet undefined class of feline type-C virus.