The CD40/CD40 ligand dyad and its downstream effector molecule ISG54 in relating acute neuroinflammation with persistent, progressive demyelination

Although Multiple Sclerosis (MS) is primarily thought to be an autoimmune condition, its possible viral etiology must be taken into consideration. When mice are administered neurotropic viruses like mouse hepatitis virus MHV-A59, a murine coronavirus, or its isogenic recombinant strain RSA59, neuroinflammation along with demyelination are observed, which are some of the significant manifestations of MS. MHV-A59/RSA59 induced neuroinflammation is one of the best-studied experimental animal models to understand the viral-induced demyelination concurrent with axonal loss. In this experimental animal model, one of the major immune checkpoint regulators is the CD40-CD40L dyad, which helps in mediating both acute-innate, innate-adaptive, and chronic-adaptive immune responses. Hence, they are essential in reducing acute neuroinflammation and chronic progressive adaptive demyelination. While CD40 is expressed on antigen-presenting cells and endothelial cells, CD40L is expressed primarily on activated T cells and during severe inflammation on NK cells and mast cells. Experimental evidences revealed that genetic deficiency of both these proteins can lead to deleterious effects in an individual. On the other hand, interferon-stimulated genes (ISGs) possess potent antiviral properties and directly or indirectly alter acute neuroinflammation. In this review, we will discuss the role of an ISG, ISG54, and its tetratricopeptide repeat protein Ifit2; the genetic and experimental studies on the role of CD40 and CD40L in a virus-induced neuroinflammatory demyelination model.