Differential anti-Golgi complex autoantibody production following murine lactate dehydrogenase-elevating virus infection.

Lactate dehydrogenase-elevating virus (LDV) causes asymptomatic infection and persistent viremia in mice with unique infectious specificity directed to a certain subpopulation of macrophages leading to chronic infection and an immunological disorder that includes hyperimmunoglobulinemia and production of autoantibodies. Infection with a species of LDV originally isolated from mice carrying an LDV-contaminated transplantable tumor (LDV-W) was reported to induce anti-Golgi complex antibody (AGA) production. In contrast, infection with the most common LDV species (LDV-P) was not associated with AGA production. Here we performed the first independent side by side comparison of the effects of the two LDV strains on their hosts as an initial approach to investigating the production of AGA. After viral inoculation, both LDV-W and LDV-P infected mice exhibited similar changes in lactate dehydrogenase in plasma suggesting similar viral activity. However, AGA production was observed in only the LDV-W infected mice and these mice exhibited plasma IgG elevation and immune complex formation. These data validated the differential potential of LDV-W and LDV-P in the production of AGA. Future comparative characterizations in the immune processing of Golgi complex autoantigens using these viral strains may be useful in obtaining specific insights in the specific anti-Golgi complex autoimmune responses.

Persistent infection of mice by lactate dehydrogenase-elevating virus: transient virus replication in macrophages of the spleen.

In order to assess whether the spleen is the major site of replication of lactate dehydrogenase-elevating virus (LDV) in mice during the acute phase of infection, LDV replication in the spleen was measured by electron microscopy and fluorescent antibody staining of tissue sections and northern hybridization of total spleen RNA with an LDV-specific cDNA probe, and the effect of splenectomy on LDV replication was determined. LDV RNA and antigens and infected cells, presumably macrophages, were present in the spleen in high concentrations 18-25 h post infection, but then rapidly disappeared to undetectable levels during the next 1-2 days. Thus, LDV clearly replicates in the spleen during the initial phase of infection, but LDV replication in the spleen is transient due to the cytocidal nature of LDV replication and destruction of all permissive macrophages in the spleen. Furthermore, spleen macrophages do not seem to represent the major source of LDV released into the circulation, since LDV viremia as well as anti-LDV antibody production were the same in splenectomized and control animals for at least 28 days postinfection.

Structure and chemical-physical characteristics of lactate dehydrogenase-elevating virus and its RNA.

Lactate dehydrogenase-elevating virus (LDV) was purified from culture fluid of infected primary cultures of various mouse tissues (peritoneal macrophage, bone marrow, spleen, and embryo) and from plasma of infected mice. Electron microscopy of negatively stained virus and positively stained sections of LDV revealed spherical particles of uniform size with a diameter of about 55 nm, containing an electron-dense core with a diameter of about 30 nm. During sample preparation the envelope had a tendency to slough off and disintegrate to form aggregates of various sizes and small hollow particles with a diameter of 8 to 14 nm. Two strains of LDV exhibited a density of 1.13 g/cm3 in isopycnic sucrose density gradient centrifugation whether propagated in primary cultures of the various mouse tissues or isolated from plasma of infected mice. A brief incubation of LDV in a solution containing 0.01% Nonidet P-40 or Triton X was sufficient to release the viral nucleocapsid, whereas a similar treatment had no effect on Sindbis virus. The nucleocapdis of LDV exhibited a density of 1.17 g/cm3, was devoid of phosphatidylcholine, and contained only the smallest of the viral proteins, VP-1, which had a molecular weight of about 15,000. The envelope contained two proteins. VP-2 with a molecular weight of 18,000 and a glycoprotein, VP-3, which migrated heterogenously (24,000 to 44,000 daltons) during polyacrylamide gel electrophoresis. When compared to the sedimentation rate of 29S rRNA, the RNAs of LDV and Sindbis virus sedimented at 48 and 45S, respectively, whether analyzed by zone sedimentation in sucrose density gradients containing low or high salt concentrations or denatured by treatment with formaldehyde. Our results indicate that LDV should be classified as a togavirus, but that LDV is sufficiently different from alpha and flaviviruses to be excluded from these groups.

Purification and electron microscopy of lactic dehydrogenase virus of mice.

Lactic dehydrogenase virus (LDV) was purified from infectious ascites fluid of mice bearing Ehrlich tumours using Sepharose gel filtration and rate zonal and isopycnic sedimentation. In glycerol gradients, a sedimentation coefficient of about 200S and a buoyant density of 1-14 g/ml was determined for the virus particle. Spherical particles with diam. between 62 and 80 nm, depending on the method of fixation and staining, have been identified electron microscopically. The virus particle consists of a spherical nucleocapsid wrapped into a double-layered envelope. The nucleocapsids, isolated by treatment with NP40 and purified by centrifuging on sucrose gradients had a sedimentation coefficient of 176S. Electron micrographs show spherical particles with a diam of 35 plus or minus nm. Classification of LDV as a member of the togaviridae family is discussed.