Riley virus neutralizing activity in the plasma of infected mice with persistent viraemia

Increased efficacy of the immunoglobulin G2a subclass in antibody-mediated protection against lactate dehydrogenase-elevating virus-induced polioencephalomyelitis revealed with switch mutants

Immunoglobulin G1 (IgG1), IgG2a, and IgG2b switch variants were derived from an IgG3 monoclonal antibody directed against the VP3 envelope glycoprotein of lactate dehydrogenase-elevating virus (LDV). Among the four antibodies, IgG2a delayed the onset and progression of LDV-induced polioencephalomyelitis more than did the other subclasses. This suggests that the IgG2a predominance observed in many IgG antibody responses elicited by live viruses could, at least under some circumstances, correspond to the selection of the best protection for the infected host.

Antibody response of mice to lactate dehydrogenase-elevating virus during infection and immunization with inactivated virus

BALB/c and Swiss mice were infected with lactate dehydrogenase-elevating virus (LDV) or immunized with glutaraldehyde-inactivated or ether-extracted virus and their plasma was monitored for anti-LDV IgG and IgM levels by ELISA and indirect fluorescent antibody staining, for neutralizing antibodies, for sensitized antibody-virus complexes, for immune complexes, and for total plasma IgG and IgM. In infected mice, anti-LDV IgM was transiently formed during the first 2 weeks post infection (p.i.) but only at a low level. Anti-LDV IgG was produced in a biphasic manner with an initial peak at about 10 days p.i. and a secondary rise reaching a maximum level 30-80 days p.i. which was retained throughout the persistent phase of infection. The concomitant appearance of comparable levels of low molecular weight immune complexes suggests that most anti-LDV IgG was complexed with LDV proteins. Also, as early as 10 days p.i., infectious antibody-LDV complexes developed, which were neutralizable by rabbit anti-mouse IgG, whereas antibodies that neutralize the infectivity of exogenously added LDV appeared only 1-2 months p.i. Throughout infection, most of the anti-LDV IgG was directed to VP-3, the envelope glycoprotein of LDV, which was found to exist in at least 10 distinct forms ranging in molecular weight from 24 to 42 kDa. Anti-LDV IgG levels as high as those observed in infected mice developed in mice immunized with inactivated LDV. Antibodies to glutaraldehyde-inactivated LDV were also mainly directed to VP-3, but exhibited no neutralizing activity. The polyclonal B cell activation associated with a persistent LDV infection and the formation of immune complexes were not observed in mice immunized with inactivated virus.

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.

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.

Immune response to lactate dehydrogenase-elevating virus: serologically specific rabbit neutralizing antibody to the virus

A rabbit was immunized with large amounts of the lactate dehydrogenase-elevating virus (LDV) over a 9-month period. The plasma from this rabbit possessed an anti-LDV IgG titer of 1:80,000 as measured by the enzyme-linked immunosorbent assay (ELISA) method and a neutralizing titer of 1:1,000 for the homologous strain of LDV. LDV neutralization at 4 degrees C followed single-hit kinetics. In contrast, mouse anti-LDV IgG in plasma of chronically LDV-infected mice failed to neutralize LDV at 4 degrees C and neutralization at 37 degrees C was slow, biphasic, and inefficient compared with the neutralization caused by rabbit anti-LDV IgG, even though high levels of anti-LDV IgG were detectable in mouse plasma by the ELISA method. Rabbit anti-LDV IgG neutralized one heterologous strain of LDV as rapidly as it did the homologous strain, but failed to significantly neutralize five other strains of LDV, all of which were originally isolated from different mouse strains bearing transplantable tumors. The results indicate clear serological differences between LDV strains. Cross-reactions between the strains, however, were observed by ELISA, using the antibody induced during persistent infection of mice with each LDV strain. Immunoglobulin M (IgM) from mice infected for 15 days with the various strains bound equally to our LDV strain. IgG obtained from 2-month-infected mice also cross-reacted, but to a varying extent which partly correlated with the specificity detected by neutralization. Both rabbit and mouse anti-LDV IgG enhanced the infectivity of LDV at a low multiplicity of infection for primary cultures of peritoneal mouse macrophages.

Effect of a potent interferon inducer on acute and chronic lactic dehydrogenase virus viremia

The effect of a single and multiple doses of polyinosinic-polycytidylic acid (poly (I). poly(C) on lactic dehydrogenase virus viremia has been studied. A single injection of 200 mug of poly (I)-poly(C) given 6 h before infection with lactic dehydrogenase virus caused a temporary decrease in viremia of about 2.5 log10. Repeated injections of 100 mug of poly(I)-poly(C) every 24 h beginning at -24 h caused a temporary decrease in viremia of about 4.0 log 10. Therapeutic treatment with optimal dosage schedules (100 mug every 24 h) caused a reduction in viremia of 1.0 to 2.0 log10. This decrease lasted for at least 24 h after the treatment was stopped. Some possible reasons for the limited effectiveness of poly (I)-poly(C) in this system are discussed.

Immunodepression by Rowson-Parr virus in mice. I. Growth curves of Rowson-Parr virus and immunological relationships with Friend virus

The growth curve of Rowson-Parr virus (RPV) was studied in the spleen of mice infected with RPV only and of mice infected with Friend virus (FV) preparations, which consist of a mixture of RPV and FV. In mice infected with FV preparations, RPV replicated to a higher titer than FV and attained higher levels than in singly infected mice. The chronic viremia of RPV-infected mice was found to coexist with circulating anti-RPV antibodies. These antibodies also neutralize FV and are probably responsible for the resistance against FV conferred to mice by prior infection with RPV.

Induction of bone marrow colony-stimulating activity by a filterable agent in leukemic and normal mouse serum

1. Leukemic Swiss mice of ICR/Ha strain which had been injected at birth with a lymphoid-leukemia-inducing virus preparation yielded sera which produced elevations of serum colony-stimulating activity within 16 hr and significant plasma-LDH-enzyme elevation at 4 days when injected intraperitoneally into normal ICR/Ha Swiss mice. Colony-stimulating activity was assayed in vitro by the stimulation of hemopoietic colony formation by DBA/1 bone marrow cells. 2. The inducing agent in leukemic serum was passageable, filterable, sedimentable, and heat-, ether-, and UV-labile. 3. A similar agent was recovered from normal Swiss serum after blind serial passages through normal mice. 4. LDH elevating virus induced a similar elevation of serum colony-stimulating activity when injected at high titers, and cross-resistance was demonstrated between LDH virus and the passaged leukemic serum agent.

Spontaneous mammary tumors: decrease of incidence in mice infected with an enzyme-elevating virus

Mice infected with a virus which causes increased activity of lactate dehydrogenase, and of other enzymes in blood plasma, had a significantly lower incidence of spontaneous mammary carcinoma than did controls. When the experiment was terminated at 18 months, the incidence of mammary tumors in controls was 90 percent, and in infected mice, 53 percent.