Targeted recombination between MHV-2 and MHV-A59 to study neurotropic determinants of MHV.

MHV-A59 produces acute encephalitis, acute hepatitis and chronic demyelination in infected mice. MHV-2 produces only hepatitis and mild meningitis but without encephalitis or demyelination. We have previously studied a set of recombinant viruses between these two strains.

The pathogenesis of MHV nucleocapsid gene chimeric viruses.

A set of viruses in which various segments of the nucleocapsid (N) gene of MHV have been substituted with the corresponding segments of bovine coronavirus (BCV) by targeted recombination were analyzed for their biologic properties. Histology for organ pathology and plaque assay for viral titer analysis following intracerebral (IC) inoculation were studied. One chimeric virus (Alb85), in which only a small segment of the N gene was replaced, exhibited a phenotype similar to wild type MHV-A59.

Coronavirus MHV-A59 causes upregulation of interferon-beta RNA in primary glial cell cultures.

Infection of mice with coronavirus mouse hepatitis virus strain MHV-A59 causes focal acute encephalitis, hepatitis and chronic demyelinating disease. To investigate host interferon (IFN) response to viral infection within the brain, RNA was extracted from A59-or MHV-2- infected and mock-infected primary astrocyte cultures from newborn mice, RT-PCR amplified RNA with primers specific for the various IFNs, transferred to nylon membranes and hybridized with IFN specific digoxigenin-labeled probes. Infection of primary astrocyte cultures from newborn mice with either A59 or MHV-2 caused upregulation of IFN-beta RNA, but not IFN-gamma or IFN-alpha.

Altered CD40 ligand induction in tolerant T lymphocytes.

CD40 ligand (CD40L) is a member of the tumor necrosis factor superfamily and is expressed on the surface of activated T lymphocytes. The interaction of CD40L with CD40 on B cells results in B cell activation, immunoglobulin (Ig) secretion and Ig class switching. To study anergy as a mechanism of murine CD4 T cell tolerance, we determined both in vivo and in vitro that CD3-activated anergic cells are deficient in the ability to stimulate B cell proliferation, and that anergic cells are defective for the T cell receptor/CD3-mediated induction of CD40L expression.

Induction of interleukin 12 responsiveness is impaired in anergic T lymphocytes.

The cytokine, interleukin 12 (IL-12), stimulates both natural killer cells and T cells to proliferate and to secrete interferon gamma (IFN-gamma). The T cell proliferative response to IL-12 must be induced and is evident after T cell receptor-mediated stimulation. As reported here, tolerant CD4+ T cells and clones, that are anergic for IL-2 production, are also anergic for induction of the proliferative response to IL-12.