MOUSE THYMIC VIRUS (MTLV)

Mouse Thymic Virus ("MTLV"; murid herpesvirus 3), a naturally occurring lymphotropic herpesvirus, causes thymic necrosis in newborn mice, resulting from selective depletion of T cells bearing the surface marker CD4. After thymic regeneration, virus is shed indefinitely in saliva and from salivary glands. Although the cell involved in chronic infection is unknown, a T cell subpopulation may be required. MTLV is therefore a model for T lymphotropic virus infection and for thymic T cell depletion and regeneration. Accurate detection of MTLV has become an urgent priority since the recently instituted FDA requirement that hybridomas be tested for MTLV. This application proposes the following research: 1. Present ELISA screening of MTLV in mouse colonies will be extended in order to provide further estimates of prevalence. Little is known about comparative responses to infection (seroconversion, virus shedding) of different mouse strains, essential for validating diagnostic procedures; this will be defined for several strains C57BL/6, A/J, C3H/HeJ, AKR, SWR, and BALB/c [By type]). Mice will be inoculated with a range of virus doses; extent and duration of seroconversion (by ELISA), virus shedding (mouthswabs), and (in newborns) thymic necrosis will be determined for each dose. Strains showing very high or low susceptibility will be retested at additional doses. The limitations of present assay techniques necessitate additional tools for improved detection and research; to provide these tools, the antigen-based diagnostic techniques of competition ELISA (cELISA) and immunocytochemistry will be further developed, validated, and compared with infectivity assay. 2. Virus in T lymphocyte subpopulations will be determined after cell sorting. Mice undergoing thymic necrosis also show necrosis of splenic T dependent areas. T cells in necrotic and regenerating spleens, and in peripheral blood, will be phenotyped using appropriate markers (CD4, CD8, and CD5); histopathologic correlations will be made. The different strains will be compared. Macrophages will also be tested for virus and ability to support viral replication. Immunocytochemistry will be used to identify infected cells in spleen, salivary gland, and leukocytes. 3. We have found autoantibody production in mice 2-3 months after neonatal MTLV infection. This will be further defined by comparing autoantibody induction in strains known to vary in susceptibility to autoimmunity induced by thymic damage. Autoimmune disease will be evaluated histopathologically, and adult-infected mice compared with neonatally-infected animals. 4. MTLV biologically resembles human herpesvirus-6/HBLV (HHV-6). To evaluate the potential of MTLV as a possible model for HHV-6, possible similarities and relationships between MTLV and HHV-6 will be defined by Southern blotting (at the DNA level), and Western blotting, (at the protein level). Effect of antiviral agents (Acyclovir, Ganciclovir, and others) will be defined for MTLV and compared with known data on HHV-6.