Tyro3 deletion is protective in experimental autoimmune encephalomyelitis

Multiple sclerosis is a complex neurological disorder, involving both the adaptive and innate immune systems as well as the CNS. The interaction between these systems is complex, and as such, there is the potential for MS therapies to have conflicting effects in different tissues. It is therefore critical that in addition to tissue-specific studies, system-wide effects of potential therapeutic pathways are explored. The circulating protein Gas6 is a promising therapy to promote remyelination in people with multiple sclerosis. Gas6 is a ligand for the TAM family of receptor protein tyrosine kinases that are widely expressed in the immune system and in the CNS, highlighting the potential for multi-system effects as a result of Gas6 treatment. In this study, we demonstrate that global genetic deletion of either Gas6 or the Gas6 receptor Tyro3 results in reduced disease severity following induction of experimental immune encephalomyelitis in mice. The reduction in severity was accompanied by increased expression of both IL-4 and IL-17A in Tyro3 KO mice lymph node tissue and decreased expression of both cytokines in spinal cord tissues. IL-4 is a cytokine known to be protective in inflammatory demyelination in mice. Conversely, the cytokine IL-17A is known to be pathological. The overall shift to reduced disease severity highlights the multi-faceted role of TAM receptor signaling in inflammatory demyelination.