Elevated gamma-globulin and increased antibody production in mice infected with lactic dehydrogenase virus

Multiplex fluorescent immunoassay for detection of mice infected with lactate dehydrogenase elevating virus

Commercially available diagnostic tools for the detection of lactate dehydrogenase elevating virus (LDV) infection have been restricted to measurement of serum lactate dehydrogenase (LDH) activity levels and detection of the viral genome by RT-PCR assays. Serologic diagnosis of LDV infection has not been widely adopted due to the belief that the formation of antigen-antibody complexes and B-cell polyclonal activation may confound interpretation of results. In the current study, we inoculated BALB/c, C57BL/6, and Swiss Webster mice with LDV to compare the diagnostic reliability of a commercially available multiplex fluorescent immunoassay for the detection of antiLDV antibodies with that of the LDH enzyme assay. The serologic assay was vastly more sensitive and specific than was the LDH enzyme assay. Moreover, the serologic assay detected antiviral antibodies throughout the 3-mo time course of this study. These results suggest that antigen-antibody complex formation and polyclonal B-cell activation had little effect on assay performance.

Polyclonal Hypergammaglobulinemia and Formation of Hydrophobic Immune Complexes in Porcine Reproductive and Respiratory Syndrome Virus-Infected and Uninfected Pigs

Infection of young conventional, domestic pigs with porcine reproductive and respiratory syndrome virus (PRRSV) strains VR2332 and JA142 resulted in a rapid, progressive increase in serum IgG reaching maximum levels of 20-30 mg/mL at about 3 weeks post infection (p.i.), which were maintained until at least 63 days p.i., whereas the level of serum IgG remained at 4-6 mg/mL in sham infected pigs. In most of the VR2332 and JA142-infected pigs hypergammaglobulimenia was associated with the formation of hydrophobic, 150-300-kDa IgG-containing immune complexes that bound in the presence of 0.1% Tween 20 to ELISA plates that were not coated with any antigen. The ELISA plate-binding activity remained low in most infected pigs, but reached high levels in some JA142-infected pigs. Binding of the immune complexes was also observed, but at a lower level, to uncoated ELISA plates in the peptide ELISA for anti-PRRSV Abs. The immune complexes bound to uncoated ELISA plates with a much lower affinity than Abs to plates coated with peptides containing the appropriate epitopes. The immune complexes also bound to HerdChek ELISA plates, but because of low binding affinity for these plates, the bound complexes were removed by the repeated washes with Tween 20 solution. Overall the PRRSV-induced hypergammaglobulinemia and generation of ELISA plate-binding immune complexes resembled those observed in mice infected with the closely related lactate dehydrogenase-elevating virus (LDV) and thus, like the latter, seem a result of a polyclonal activation of B cells. We also found that sera of a group of older sows possessed high levels of IgG as well as of ELISA plate-binding immune complexes, in spite of being PRRSV infection negative by all criteria presently available. On the other hand, sera from wild hogs contained no ELISA plate-binding IgG in spite of possessing high total serum IgG levels.

N-glycans on the short ectodomain of the primary envelope glycoprotein play a major role in the polyclonal activation of B cells by lactate dehydrogenase-elevating virus

The common biologically cloned isolates of lactate dehydrogenase-elevating virus (LDV-P and LDV-vx) invariably cause a polyclonal activation of B cells in immunocompetent mice. It is recognized by an at least 10-fold increase in plasma IgG2a levels and the de novo formation of immune complexes that most likely consist of autoantibodies and their antigens. The present study indicates that three closely spaced N-glycans on the short ectodomain of the primary envelope glycoprotein, VP-3P, of LDV-P/vx, play a major role in inducing the polyclonal proliferation of B cells. IFN-gamma then seems to mediate the differentiation of the activated B cells to IgG2a-producing plasma cells. These conclusions are based on the finding that the IgG2a hypergammaglobulinaemia and immune complex formation were much lower in mice that were infected with LDV variants (LDV-C and LDV-v) whose VP-3P ectodomains lack two of the three N-glycans than in LDV-P/vx infected mice. In contrast, the VP-3P ectodomains of three neutralization escape variants of LDV-C/v whose VP-3P ectodomains possess three N-glycosylation sites caused a polyclonal activation of B cells comparable to that of LDV-P/vx.

Regulation of immune complexes during infection of mice with lactate dehydrogenase-elevating virus: studies with interferon-gamma gene knockout and tolerant mice

Mice persistently infected with lactate dehydrogenase-elevating virus (LDV) develop circulating IgG-containing hydrophobic immune complexes, with a molecular mass of 150 to 300 kd, which bind to the surfaces of high-capacity enzyme-linked immunosorbent assay (ELISA) plates. LDV infection also stimulates polyclonal B-cell activation and autoimmunity. For this study, interferon-gamma gene knockout (GKO) mice were utilized to study circulating immune complexes and other parameters of LDV infection. The kinetics of LDV viremia, formation of plasma IgG anti-LDV antibodies, and LDV replication in the spleen and liver were essentially normal in GKO mice. Polyclonal activation of B cells, as reflected by increased total plasma IgG concentration during LDV infection, was found to be intact in GKO mice, although at a lower magnitude than in control mice. The plasma concentration of IgG-containing hydrophobic immune complexes was reduced about 75% in LDV-infected GKO mice relative to normal LDV-infected controls. Allogeneic tissue responses were also found to be reduced in LDV-infected GKO mice relative to those in normal LDV-infected controls. These results dissociate specific anti-LDV immunity from formation of hydrophobic immune complexes, show that the IgG anti-LDV response as well as LDV replication in the spleen and liver are insensitive to physiological levels of interferon (IFN)-gamma, and suggest that IgG-containing immune complexes stimulated by LDV infection are a marker for autoimmunity.

Lactic dehydrogenase virus infection enhances parasite egg production and inhibits eosinophil and mast cell responses in mice infected with the nematode Nippostrongylus brasiliensis

The effects of lactic dehydrogenase virus (LDV) infection on the protective immune responses to the nematode Nippostrongylus brasiliensis were studied. Mice with chronic LDV infection showed significantly higher levels of parasite egg production than non-LDV-infected (control) mice after N. brasiliensis infection. Concurrent LDV infection also suppressed peripheral blood eosinophilia and the lung mastocytosis induced by this nematode. LDV infection showed higher expression levels of the interferon-gamma (IFN-gamma) mRNA in lymph nodes compared with control mice before N. brasiliensis infection. In addition, the IgG2a production in LDV-infected mice was higher than that in control mice before and after N. brasiliensis infection. These results suggest that LDV infection modulates protective immune responses against N. brasiliensis infection by the activation of T-helper type 1 cells.

Influence of viral infection on anti-erythrocyte autoantibody response after immunization of mice with rat red blood cells

Natural or deliberate activation of the immune system of pathogen-free mice markedly affected their response to an autoimmune-inducing stimulus. Specifically, mice immunized with rat red blood cells were found to make antibodies reactive with both rat and mouse erythrocytes. Animals housed for an extended period in a conventional environment developed an autoimmune response twice as fast as those kept in isolators. In an attempt to emulate this effect, mice kept in a sterile environment were infected with a potent polyclonal activator of B lymphocytes, lactate dehydrogenase-elevating virus, at the same time as they were inoculated with rat erythrocytes. Whereas uninfected animals developed a progressively increasing autoantibody titer, infected mice quickly attained high anti-erythrocyte autoantibody titers that remained rather constant. Contrary to circulating autoantibodies, bound anti-erythrocyte antibodies decreased with time. Virus infection enhanced all the IgG subclass responses, with the exception of IgG1, to both rat and mouse erythrocytes. None of the modifications of the autoimmune responses resulted in anemia.

Lactate dehydrogenase-elevating virus, equine arteritis virus, and simian hemorrhagic fever virus: a new group of positive-strand RNA viruses

The last comprehensive reviews of nonarbotogaviruses included discussions on pestiviruses, rubella virus, lactate dehydrogenase-elevating virus (LDV), equine arteritis virus (EAV), simian hemorrhagic fever virus (SHFV), cell fusion agent, and nonarboflaviviruses. The inclusion of all these viruses in the family Togaviridae was largely based on the similarities in morphological and physical–chemical properties of these viruses, and in the sizes and polarities of their genomes. In the intervening years, considerable new information on the replication strategies of these viruses and the structure and organization of their genomes has become available that has led to the reclassification or suggestions for reclassification of some of them. The replication strategy of EAV resembles that of the coronaviruses, involving a 3'-coterminal nested set of mRNAs. Therefore, EAV has been suggested to be included in a virus superfamily, along with coronaviruses and toroviruses. Recent evidence indicates that LDV not only resembles EAV in morphology, virion and genome size, and number and size of their structural proteins, but also in genome organization and replication via a 3'-coterminal set of mRNAs. SHFV, although not fully characterized, exhibits properties resembling those of LDV and EAV, and the recent evidence suggest that it may possess the same genome organization as these viruses. The three viruses may, therefore, represent a new family of positive-strand RNA viruses and are reviewed together in this chapter. In this chapter, emphasis is on the recent information concerning their molecular properties and pathogenesis in vitro and in vivo and on the host immune responses to infections by these viruses.

Immune complexes that bind to ELISA plates not coated with antigen in mice infected with lactate dehydrogenase-elevating virus: relationship to IgG2a- and IgG2b-specific polyclonal activation of B cells

We have further investigated the nature of IgG-containing complexes of 150-300 kD that rapidly appear in the circulation of mice of various strains after infection with lactate dehydrogenase-elevating virus (LDV) and are recognized and quantitated by their binding in the presence of 0.05% Tween 20 to certain enzyme-linked immunosorbent assay (ELISA) plates with high protein affinity that have not been coated with protein antigen (5). These binding complexes have been found to contain primarily IgG2a or, in some mice, IgG2b. Their isotype specificity and time course of formation correlated with those of the polyclonal production of immunoglobulins in these mice, as measured by increases in total IgG2a or IgG2b in the circulation. In contrast, anti-LDV antibodies exhibited much broader isotype specificities in all mouse strains investigated. Depletion of BALB/c mice of CD4+T cells or lack of T cells in nude Swiss mice only partly reduced the polyclonal activation of B cells and the formation of ELISA plate-binding complexes, whereas anti-LDV antibody formation was completely blocked. Only a small proportion of the total IgG2a or IgG2b formed as a result of the LDV-induced polyclonal activation of B cells was recovered in plate-binding complexes, which sedimented in sucrose density gradients between 150 and 300 kD. Diverse monoclonal antibodies of different IgG isotopes did not bind to the plates at concentrations at which LDV-induced immune complexes exhibited binding activity. We suggest that the LDV-induced immune complexes do not contain anti-LDV antibodies, but are complexes of auto-antibodies and self-antigen(s). However, additional features must be responsible for the high affinity of these complexes for ELISA plates since various immune complexes formed in vitro failed to bind to the plates, and binding activity of the immune complexes formed in LDV-infected mice could not be regenerated in vitro once the complexes had been dissociated by a low pH treatment.

Polyclonal B cell activation of IgG2a and IgG2b production by infection of mice with lactate dehydrogenase-elevating virus is partly dependent on CD4+ lymphocytes

Concentrations of IgM and IgG isotypes were determined by capture ELISA in plasma of Swiss, BALB/c and C58/M mice. Plasma IgG isotype concentrations, especially of IgM, IgG1 and IgG2a, varied considerably between mouse strains, batches of mice of the same strain and individual mice and as a function of age. Infection of the mice with LDV, which is known to replicate primarily in a subpopulation of macrophages, consistently resulted in a rapid elevation of plasma IgG2a (or of IgG2b in some Swiss nu/+ mice), but no plasma IgG increases were observed in mice immunized with inactivated LDV. Plasma IgG2a elevation after LDV infection was greatly delayed and reduced by depletion of the mice of CD4+, but not of CD8+, T cells by administration of protein-G-purified anti-CD4 or anti-CD8 mAbs, and completely inhibited by repeated treatment of the mice with cyclophosphamide. Treatment with anti-CD4 mAbs, or cyclophosphamide also greatly reduced the production of anti-LDV antibodies, while not significantly affecting the replication of LDV in these mice. Nude Swiss mice also failed to produce anti-LDV antibodies, though supporting normal LDV replication. Plasma IgM, IgG1, IgG2a and IgG2b levels increased in LDV-infected nu/nu mice, but similar changes were observed in uninfected mice. The results indicate that the LDV-induced polyclonal activation of B cells requires productive LDV infection of mice and is, at least partly, dependent on functioning CD4+ cells. They suggest that productive infection of the LDV-permissive subpopulation of macrophages leads to the activation of CD4+ T lymphocytes of subset 1 and their Spleen cells from 5-day LDV-infected BALB/c mice incorporated [3H]thymidine 2-3 times more rapidly in vitro than spleen cells from companion uninfected mice, whereas their responses to concanavalin A and lipopolysaccharide were reduced 60-70%.

Physiological relationships among stress, viruses, and cancer in experimental animals

Anxiety-induced psychoneural stimulation, via the hypothalamic-pituitary axis, activates the adrenal cortex to release corticosteroids, which elicit various alterations of corticoid-sensitive cell-mediated immunologic processes. Stress sensitive murine tumor-host experimental models have been utilized to demonstrate various effects of stress upon aspects of tumor development. Although many of the observed anxiety-induced alterations of tumor-related parameters can be interpreted in terms of corticoid-induced modifications of immune functions, other observations are more difficult to interpret, and may be caused in part by corticosteroid-independent modulation of lymphocyte functions. In the case of tumors induced by oncogenic viruses, anxiety-induced plasma corticoid elevations may also act independently of the immune system to stimulate tumor development via hormone binding sites on proviral DNA. Rigorously controlled environmental and experimental conditions are fundamental for the demonstration and interpretation of stress-related phenomena. Technical prerequisites include protective animal facilities, special handling procedures, the use of nontraumatic stressors, and the recognition of vital psychosocial, coping and timing factors. Various biologic factors, such as sex, genetic substrain differences and common interfering viral infections, must also be controlled or taken into consideration.

Potential detrimental effects of rodent viral infections on long-term experiments

Healthy animals are of paramount importance in obtaining meaningful, reliable scientific results. Viral infections of rodents often have a significant impact on various types of biomedical research. Laboratory animal specialists and researchers must be aware of the possible consequences associated with the use of infected animals. The objective of the paper is a discussion of the frequently encountered viral infections that can complicate or invalidate the interpretation of results by altering the host's response.

Cellular immunity changes caused by LDH virus: analogy with observations of neuroblastoma-bearing mice

Evidence is presented that LDH virus infection of mice results in drastic changes in several immune activities. Serum IFN titer and splenic NK activity are increased during the acute phase of infection. NK stimulation is mediated by IFN-alpha,beta since injection of an antibody against murine IFN-alpha,beta is able to abolish the effect. IL-2 production is inhibited throughout the study period following injection of LDH virus (14 days), although a partial recovery is observed during the second week. Similarly, IL-2 receptor expression and MLC responsiveness are suppressed. This suppression lasts for 2 and 7 days respectively after injection. Addition of recombinant IL-2, but not of indomethacin, to the MLC cultures restores the proliferation rate. Not only proliferation but also cytotoxic cell generation in MLC is diminished during the first week after LDH virus injection. Again, this response is normalized at day 14. Additional observations indicate that LDH virus is present in murine neuroblastoma. This explains some of the previously described effects of this tumor on the cellular immune system of the host.

Isotypically restricted activation of B lymphocytes by lactic dehydrogenase virus

Lactic dehydrogenase elevating virus (LDV) was found to selectively stimulate IgG2a synthesis in infected mice. Within one week after infection, the production of IgG2a increased nearly 50-fold whereas that of IgM, IgA, IgG1 and IgG3 remained virtually unchanged. IgG2b synthesis was also enhanced but to a lesser extent. Several observations suggested that this stimulation of IgG2 production resulted from a polyclonal B cell activation: (a) the isoelectric focusing patterns of IgG2a before and after LDV infection were exactly the same, (b) the frequency of clones with anti-LDV activity in hybridoma collections derived from infected mice was extremely low (less than 4/1000) and (c) the proliferative response elicited by LDV in unsensitized animals was comparable with that induced by lipopolysaccharide. The effect of LDV on immunoglobulin synthesis was drastically reduced in nude mice but was not affected by the X-linked B lymphocyte defect of animals carrying the xid mutation.

Immunoglobulin classes of Aleutian disease virus antibody

Aleutian disease virus (ADV) persistently infects mink and causes marked hypergammaglobulinemia. Immunoglobulin class-specific antisera were used to define the total immunoglobulin of each class by radial immunodiffusion and the immunoglobulin class of ADV-specific antibody by immunofluorescence in experimentally and naturally infected mink. Electrophoretic gamma globulin closely reflects the immunoglobulin G (IgG) level in mink, and the majority of the increased immunoglobulin and ADV antibody in infected mink is IgG. IgM becomes elevated within 6 days after infection, reaches peak levels by 15 to 18 days, and returns to normal by 60 days after infection. The first ADV antibody demonstrable is IgM, and most mink have virus-specific IgM antibody for at least 85 days postinfection. Serum IgA levels in normal mink are not normally distributed, and ADV infection causes a marked elevation of IgA. Low levels of ADV-specific IgA antibody can be shown throughout the course of infection. Failure of large amounts of virus-specific IgG antibody to inhibit the reaction of virus-specific IgM and IgA antibodies suggests that the various classes of antibodies are directed against spatially different antigenic determinants. The IgM and IgA were shown not to be rheumatoid factors.

A tumor-associated lactic dehydrogenase virus suppresses the host resistance to infection with Listeria monocytogenes

Infection of mice with lactic dehydrogenase virus (LDV) causes a lifelong chronic infection which is followed by alterations in immune responses during the acute phase of the infection. LDV was found to impair many functions of the reticuloendothelial system and to suppress macrophage-dependent immune responses. We tested the effect of acute infection with LDV in mice on the macrophage-mediated resistance to infection with a virulent bacterium. We found that LDV reduces the host's capacity to resist infection with Listeria monocytogenes. Many tumor lines which are transferred in mice are infected with LDV, and their growth rate is affected by the presence of the virus. It is therefore important to distinguish between immune alterations in tumor-bearing mice which are caused by the progressive growth of the tumor and those which are secondary to the viral infection. We tested whether LDV and a circulatory factor from tumor-bearing mice with similar suppressive effects on anti-Listeria immunity are two different entities or whether they are similar. We found that the factor is associated with LDV-infected tumor cells and is absent in LDV-free tumor cells. Other biological and physical characteristics supported the assumption that the tumor-associated factor is the LDV.

Effect of infections with swine fever virus on immune functions. III. Antibody response to lipopolysaccharide and sheep red blood cells

In order to determine the effect of infections with low-virulent swine fever virus (SFV) on antibody responses, pigs were administered lipopolysaccharide (LPS) or sheep red blood cells (SRBC), 2 days after infection. Infected pigs showed an enhanced primary response to LPS late during infection. The secondary response to LPS seemed to be unaffected. Both the primary and secondary antibody response to SRBC appeared to be enhanced rather than depressed in infected pigs. These in vivo findings suggest that pigs infected with low-virulent SFV do not develop a depression of B lymphocyte function.

Immune response to lactate dehydrogenase-elevating virus: isolation of infectious virus-immunoglobulin G complexes and quantitation of specific antiviral immunoglobulin G response in wild-type and nude mice

Lactate dehydrogenase-elevating virus (LDV) causes a normally benign persistent infection of mice, resulting in a life-long viremia characterized by the presence of circulating infectious immune complexes, impaired clearance of certain enzymes from the blood, and modification of the host immune response to various heterologous antigens. In this study, we isolated infectious immunoglobulin G (IgG)-LDV complexes in the plasma of persistently infected mice by adsorption to and elution from protein A-Sepharose CL-4B. We found that practically all infectious LDV in the plasma of persistently infected mice is complexed to IgG. LDV infectivity in these complexes was partially neutralized, but could be reactivated by treatment with 2-mercaptoethanol. We also quantitated total plasma IgG and anti-LDV IgG in wild-type and nude Swiss and BALB/c mice as a function of the time after infection with LDV by radial immunodiffusion and an enzyme-linked immunosorbent assay, respectively. Total plasma IgG levels nearly doubled in BALB/c mice during 150 days of infection. IgG levels in uninfected nude mice were only 20% of those in uninfected BALB/c mice, but during infection with LDV increased to approximately those found in uninfected BALB/c mice. Anti-LDV IgG levels were almost as high in nude mice as in normal BALB/c mice. Isoelectric focusing of purified IgG from BALB/c mice showed that LDV infection resulted in the enhanced synthesis of all 16 normal IgG fractions that we could separate by this method, which suggests that LDV infection results in polyclonal activation of IgG-producing lymphocytes.

Exacerbation of murine malaria by concurrent infection with lactic dehydrogenase-elevating virus

The simultaneous infection of mice with lactic dehydrogenase-elevating virus (LDV) and Plasmodium yoelii resulted in an exacerbated attack of malaria. Peak parasitaemia was higher and the patent infection more prolonged in doubly infected mice. The results indicate that contamination with LDV must be considered when a change in parasite virulence is observed, particularly when the parasite is maintained by blood passage in mice.

Immune reactivity of Visna virus-inoculated mice

Visna virus inoculation of mice before immunization with unrelated antigens caused suppression of humoral and cell-mediated immune responses. The immunosuppressive effect was dependent on the virus dose and time of administration. The number of "background" antibody-producing spleen cells increased slightly after inoculation of Visna virus. Heat treatment of Visna virus abolished its immunosuppressive effect. Replication of Visna virus in mice seemed to be a prerequisite for its immunomodulating effect.

Viral oncolysate in the management of malignant melanoma. I. Preparation of the oncolysate and measurement of immunologic responses

Primary explants of human malignant melanoma were utilized in the preparation of oncolysates by Newcastle disease virus. The concentrated lysate, administered parenterally, was employed in an effort to augment antitumor immunologic responses in patients with metastatic melanoma. Observed cellular changes suggested a benefit, but humoral antibody measurements were not impressive.

Immune responses in mice infected with lactic dehydrogenase virus. I. Antibody response to DNP-BGG and hyperglobulinaemia in BALB/c mice

The humoral immune response to DNP-BGG of BALB/c mice acutely infected with lactic dehydrogenase virus (LDV) has been investigated. Virus-infected mice injected with antigen in saline exhibit a greater anti-DNP response than uninfected controls. When this antigen is presented in Freund's complete adjuvant (FCA) the anti-DNP response is greater than obtained with antigen in saline, but significant differences between infected and uninfected controls are not observed. These data are consistent with the view that acute LDV infection can have an adjuvant-like effect when this T-dependent antigen is introduced in saline. In addition, the effect of viral infection on plasma Ig class and subclass levels has been investigated. LDV infection leads to a gradual increase in plasma Ig concentration. This effect is restricted to the IgG2a subclass in most animals, but occasionally is restricted to IgG1. The mechanisms responsible for these changes have not been delineated.

Antibody-producing cells: virus-induced alteration of response to antigen

Spleen antibody-forming cells of mice yield a 3- to 10-fold increase in their response to sheep erythrocyte antigen if they are acutely infected by lactate dehydrogenase-elevating virus. This early stimulation is replaced by a long-term inhibition of the antibody-forming cells as the viremia goes into its persisting chronic stage. These contrasting immunological phenomena are examined as contributing factors responsible for the enhancement by this virus of asparaginase (EC 3.5.1.1; L-asparagine amidolydrolase) therapy against leukemia in mice, and for the alteration of the susceptibility of mice to various neoplastic processes.

Immunosuppressive activity of a subline of the mouse EL-4 lymphoma. Evidence for minute virus of mice causing the inhibition

Filtered culture fluids from the early in vitro passages of a subline of the C57BL/6 mouse EL-4 lymphoma, EL-4(G-), were strongly inhibitory for BABL/c vs. C57BL/6 mixed lymphocyte cultures (MLC). The inhibitory activity could be preserved by storage at -75 degrees C or 4 degrees C, thus allowing its further characterization. The inhibitory factor was particulate (nondialyzable, sedimentable at 100,000 g for 1 h), very small (recovered after 0.10 mum filtration), sensitive to UV irradiation, but heat stable (56 degrees C, 1 h) and resistant to chloroform. It was infectious, since later, noninhibitory passages of EL-4(G-) tissue culture cells became strongly inhibitory upon inoculation with the culture fluid. This data was consistent with the inhibitory factor being an infectious virus. Virus analysis by mouse antibody production tests revealed that viruses were indeed present in EL-4(G-) ascites cells and in the culture fluid, and not in a late passage of EL-4(G-) tissue culture cells which were not inhibitory. Neutralization of the inhibitory factor was achieved by pretreatment with ascitic fluid or with the sera raised against those (EL-4(G-)-derived materials which contained viruses. Mouse reference immune sera against minute virus of mice (MVM) completely neutralized the inhibitory factor in the culture fluid or in EL-4(G-) ascites cells. Two prototype MVM strains, and one Kilham rat virus preparation, did not inhibit the mouse MLC. Thus, the possibility exists that a variant of MVM, or an unidentified virus, has been grown and selected for in EL-4(G-) cells and recognized, due to its immunosuppressive characteristics. In any event, immunosuppression by EL-4(G-) cells was not mediated by the tumor cells, their metabolic products, or associated endogenous type C viruses, but by an exogenous virus, most likely a variant MVM with immunosuppressive characteristics. This adds weight to a parallel observation from our laboratory on the immunosuppressive effects of Kilham rat virus in rat lymphocyte cultures.

Cytomegalovirus-induced immune suppression. I. Humoral immunity

Murinecytomegalovirus (CMV) infects cells of the lymphoreticular system and causes alteration in immune function. Four to 6 days after infection, histological changes are observed in the spleen, consisting of intranuclear inclusions around germinal centres and destruction of germinal centres at higher virus inocula. Gradual healing takes place after this period. CMV also causes suppression of immune function, the maximal suppression also occurring in the 1st week after infection. Both the primary and secondary immune responses to sheep red blood cells are suppressed. The degree of immune suppression is directly related to virus inocula. When mice are first vaccinated with attenuated CMV, infection with virulent CMV results in an immune response greater than that observed in control mice.

Formation and biologic role of polyoma virus-antibody complexes. A critical role for complement

Interaction of polyoma virus, specific antibody, and complement has been studied. Firm evidence has been gathered that C1 through C3 and not C5 through C9 enhance neutralization of virus-antiviral antibody (V-Ab) complexes. C enhancement of neutralization occurs primarily by agglutination of V-Ab complexes and not by virion lysis or attachment of large protein molecules to the V-Ab complex. In this model, binding of C1, 4, 2, 3 to the V-Ab complex may explain why some viruses concentrate in or infect certain cells bearing C3 receptors such as B lymphocytes, macrophages, and monocytes.

Inhibition of antibodies to nuclear antigen and to DNA in New Zealand mice infected with lactate dehydrogenase virus

New Zealand mice developed antibodies to nuclear antigen leading to immune-complex nephritis. Humoral antibody was directed primarily against denatured DNA, although antibody to native DNA was also found. Persistent infection with lactate dehydrogenase virus significantly lowered antibodies both to nuclear antigen and to DNA in these mice. In addition, female (NZB x W)F(1) mice infected with lactate dehydrogenase virus were protected from the usual nephritic death occurring after the trapping of complexes of nuclear antigen and its antibody and of DNA and its antibody in the glomerular filter.

Divergence between immunosuppression and immunocompetence during virus-induced leukemogenesis

Mice were infected with Friend leukemia virus and later immunized with either Vibrio cholerae vaccine or sheep erythrocytes. The primary antibody response to the bacteria (as judged by the number of plaque-forming cells) was slightly enhanced by the viral infection, whereas the response to sheep erythrocytes was inhibited. The difference appeared due to sensitization of mice to antigens crossreacting with those of sheep erythrocytes; no natural immunity to V. cholerae is detectable. However, the response of mice infected with Friend leukemia virus to a secondary challenge with the cholera bacteria was markedly inhibited. Even though the number of plaque-forming cells during the primary response was not reduced, accumulation of the cells in distinct splenic foci was suppressed. These results suggest that the effect of Friend leukemia virus on immunocompetent cells is selective. The immune response appears to be susceptible to leukemia virus-induced immunosuppression only when there has been a previous stimulation of immunocytes by antigen.