Sphingosine kinase 2 regulates CD4+ T cell responses following LCMV Cl 13 infection

Viruses often establish persistent infections by interrupting immune cell responses. Sphingosine kinase 2 (SphK2) generates sphingosine 1-phsophate, which is known to regulate versatile cellular processes, including immune responses. However, little is known about the role of SphK2 in the immune response to viral infections. Here, we demonstrate that during lymphocytic choriomeningitis virus (LCMV) clone 13 infection, a virus known to establish a persistent infection in mice, SphK2 functions to limit CD4+ T cell responses, which aids in the establishment of virus-induced immunosuppression and viral persistence. The infection of SphK2-deficient (Sphk2-/-) mice with LCMV resulted in kidney disease and ultimately mortality. Following infection, Sphk2-/- mice were shown to have increased LCMV-specific CD4+ and CD8+ T cell responses. With the use of LCMV epitope-specific TCR transgenic mouse lines in adoptive transfer studies, SphK2 was shown to have intrinsic negative function in CD4+ T cells, but not CD8+ T cells. Furthermore, Sphk2-/- CD4+ T cells were able to promote endogenous, virus-specific CD8+ T cell responses more efficiently than Sphk2+/+ CD4+ T cells. Our results suggest that SphK2 is a novel regulator of the immune response during LCMV clone 13 infection and targeting SphK2 may provide a promising immunotherapeutic strategy for the control of persistent viral infections. This study incorporated the use of RNA sequencing to determine what pathways SphK2 was involved in to affect CD4+ T cell activity and proliferation. Sphk2+/+ or Sphk2-/- LCMV epitope-recognizing tg CD4+ T cells were transferred into C57BL/6 mice and recovered 7 days following LCMV Cl 13 infection. RNA sequencing revealed several pathways upregulated in Sphk2-/- CD4+ T cells relating to cell cycle progression, regulation of transcription, and regulation of nucleic acid binding. 3 replicates of LCMV-specific Sphk2+/+ CD4+ T cells from LCMV Cl 13-infected mice; 3 replicates of LCMV-Sphk2-/- CD4+ T cells from LCMV Cl 13-infected mice