Genome-Wide Mouse Mutagenesis Reveals CD45-Mediated T Cell Function as Critical in Protective Immunity to HSV-1

<div><p>Herpes simplex encephalitis (HSE) is a lethal neurological disease resulting from infection with Herpes Simplex Virus 1 (HSV-1). Loss-of-function mutations in the <i>UNC93B1</i>, <i>TLR3</i>, <i>TRIF</i>, <i>TRAF3</i>, and <i>TBK1</i> genes have been associated with a human genetic predisposition to HSE, demonstrating the UNC93B-TLR3-type I IFN pathway as critical in protective immunity to HSV-1. However, the <i>TLR3</i>, <i>UNC93B1</i>, and <i>TRIF</i> mutations exhibit incomplete penetrance and represent only a minority of HSE cases, perhaps reflecting the effects of additional host genetic factors. In order to identify new host genes, proteins and signaling pathways involved in HSV-1 and HSE susceptibility, we have implemented the first genome-wide mutagenesis screen in an <i>in vivo</i> HSV-1 infectious model. One pedigree (named <i>P43</i>) segregated a susceptible trait with a fully penetrant phenotype. Genetic mapping and whole exome sequencing led to the identification of the causative nonsense mutation L3X in the <i>Receptor-type tyrosine-protein phosphatase C</i> gene (<i>Ptprc^L3X</i>), which encodes for the tyrosine phosphatase CD45. Expression of <i>MCP1</i>, <i>IL-6</i>, <i>MMP3</i>, <i>MMP8</i>, and the <i>ICP4</i> viral gene were significantly increased in the brain stems of infected <i>Ptprc^L3X</i> mice accounting for hyper-inflammation and pathological damages caused by viral replication. <i>Ptprc^L3X</i> mutation drastically affects the early stages of thymocytes development but also the final stage of B cell maturation. Transfer of total splenocytes from heterozygous littermates into <i>Ptprc</i>^L3X mice resulted in a complete HSV-1 protective effect. Furthermore, T cells were the only cell population to fully restore resistance to HSV-1 in the mutants, an effect that required both the CD4⁺ and CD8⁺ T cells and could be attributed to function of CD4⁺ T helper 1 (Th1) cells in CD8⁺ T cell recruitment to the site of infection. Altogether, these results revealed the CD45-mediated T cell function as potentially critical for infection and viral spread to the brain, and also for subsequent HSE development.</p>