Studies on the response of SJL-J mice to infection with the lactate dehydrogenase virus

Genetic basis for Ia positivity and susceptibility to lactic dehydrogenase virus in macrophages of SJL/J mice

SJL/J mice showed a higher elevation of serum lactic dehydrogenase after lactic dehydrogenase virus (LDV) infection, and a higher per cent of Ia positive and LDV infectable cultured macrophages, than several other mouse strains. Genetic studies suggested that these unique characteristics in SJL/J mice are closely linked and inherited as a single autosomal recessive trait, which is not within the H-2 gene complex.

Pattern of infection and selective loss of Ia positive cells in suckling and adult mice inoculated with lactic dehydrogenase virus

Lactic dehydrogenase virus (LDV) infected cells were localised in cryostat sections of infected adult and suckling mice by fluorescent antibody staining. In almost every organ except brain and spinal cord, LDV infected cells were present in interstitial connective tissue, including dermis and submucosa of gastrointestinal and urinogenital tracts. They were also present in liver sinusoids and red pulp of spleen. The tissue distribution, shape, and fluorescence staining pattern of infected cells were similar in adult and suckling mice. The reactivity with monoclonal antibody to mouse macrophages (F4/80) and to Ia antigens indicated that infected cells were Ia antigen positive macrophages, and this was confirmed in double labelling experiments. Peak numbers of LDV infected cells were seen in every organ 12-18 hours post infection (p.i.), disappearing rapidly thereafter until at 48 hours p.i. they could no longer be detected. At the same time Ia positive cells fell to undetectable levels, although macrophages were still present in reduced numbers. At 7 days p.i. the total number of macrophages in sections had returned to normal, but the number of Ia positive cells remained at low levels. Macrophages recovered from peritoneal cavity and spleen of intraperitoneally infected mice were also studied. Ia positive cells had virtually disappeared from peritoneal cavity at 24-48 hours, and from spleen at 24-72 hours. Three weeks after infection the proportion of Ia positive cells was still low when compared with that of normal mice suggesting selective loss of these cells.

Detection and characterization of a lymphocyte proliferating factor (LPF) in plasma of SJL/J mice infected with the LDH virus

Infection of 25- to 30-week-old SJL/J mice with the lactate dehydrogenase (LDH) virus resulted in a transitory T-cell lymphocytopenia. However, in 40- to 45-week-old animals, the initial lymphocytopenia was followed by persistent elevations in the peripheral leukocyte counts (B and T lymphocytes). Studies indicated that this difference had its basis in a plasma factor, termed lymphocyte proliferating factor (LPF), which was induced by infection of older SJL/J mice with the LDH virus. Further experimentation revealed that plasma LPF was sensitive to storage at -60 degrees C, to heating at 90 degrees C, and to treatment with DNase. These results suggested an identification of LPF as DNA. This possibility was supported by the demonstration of LPF activity in association with DNA extracts (blood, spleen and lymph nodes from LDH virus-infected mice) which was inactivated by DNase.

Identification of lactate dehydrogenase-elevating virus as the etiological agent of genetically restricted, age-dependent polioencephalomyelitis of mice

The etiological agent of genetically restricted, age-dependent polioencephalomyelitis of mice (the ADPE agent) and several isolates of lactate dehydrogenase-elevating virus (LDV) were compared by biological, physical-chemical and antigenic criteria. The data indicate that the ADPE agent is a strain of LDV. Like LDV, the ADPE agent induced a selective elevation of plasma enzymes and splenomegaly in mice. The enzyme-elevating activity and the paralytogenic activity of the ADPE agent preparations were shown to belong to the same virus. The ADPE agent demonstrated LDV-like replication kinetics in vivo and in vitro. Moreover, the ADPE agent required primary mouse macrophages for in vitro replication, as does LDV. In turn, the LDV isolates induced a paralytic disease with ADPE-like lesions in the spinal cords of immunosuppressed C58 mice. However, the LDV isolates showed a stronger dependence on strain and age of mouse for the induction of paralysis than did the ADPE agent. The LDV isolates and the ADPE agent exhibited indistinguishable morphologies, buoyant densities, structural protein patterns, and virion ribonucleic acid sedimentation rates. Furthermore, they displayed strong antigenic cross-reactivity, as determined by cross-protection in vivo and by radioimmunoassay.