Perforin-Mediated Effector Function Within the Central Nervous System Requires IFN-γ-Mediated MHC Up-Regulation

Abstract

CD8+ T cells infiltrating the CNS control infection by the neurotropic JHM strain of mouse hepatitis virus. Differential susceptibility of infected cell types to clearance by perforin or IFN-γ uncovered distinct, nonredundant roles for these antiviral mechanisms. To separately evaluate each effector function specifically in the context of CD8+ T cells, pathogenesis was analyzed in mice deficient in both perforin and IFN-γ (PKO/GKO) or selectively reconstituted for each function by transfer of CD8+ T cells. Untreated PKO/GKO mice were unable to control the infection and died of lethal encephalomyelitis within 16 days, despite substantially higher CD8+ T cell accumulation in the CNS compared with controls. Uncontrolled infection was associated with limited MHC class I up-regulation and an absence of class II expression on microglia, coinciding with decreased CD4+ T cells in CNS infiltrates. CD8+ T cells from perforin-deficient and wild-type donors reduced virus replication in PKO/GKO recipients. By contrast, IFN-γ-deficient donor CD8+ T cells did not affect virus replication. The inability of perforin-mediated mechanisms to control virus in the absence of IFN-γ coincided with reduced class I expression. These data not only confirm direct antiviral activity of IFN-γ within the CNS but also demonstrate IFN-γ-dependent MHC surface expression to guarantee local T cell effector function in tissues inherently low in MHC expression. The data further imply that IFN-γ plays a crucial role in pathogenesis by regulating the balance between virus replication in oligodendrocytes, CD8+ T cell effector function, and demyelination.

Reduced antigen concentration and costimulatory blockade increase IFN‐γ secretion in naive CD8+ T cells

“…IFN-c is critical in the fight against infections [37]. We suggest that an early role of IFN-c involves CD8 + T cells.…”

“…APC in secondary lymphoid organs are likely not fully mature and probably display small numbers of antigenic peptides. Under such conditions, IFN-c would be the preferential response by naive CD8 + T cells, which will subsequently induce MHC expression on APC [9,[37][38][39], enhance antigen presentation, and trigger activation of macrophages [40,41]. Only at later stages, when the stimulatory capacity of the APC has been increased, CD8 + T cells would respond with proliferation and acquisition of cytolytic capacity (which we show are properties of APC displaying high levels of stimulatory molecules).…”

NKG2D Receptor Signaling Enhances Cytolytic Activity by Virus-Specific CD8+T Cells: Evidence for a Protective Role in Virus-Induced Encephalitis

“…Slides containing stained spinal cord sections were blinded and scored by three investigators, and scores were averaged and are presented as averages Ϯ standard errors of the means (SEM). The distribution of viral antigen was determined by immunoperoxidase staining (Vectastain-ABC kit; Vector Laboratories, Burlingame, CA) using the anti-JHMV MAb J.3.3 specific for the carboxyl terminus of the viral nucleocapsid protein as a primary antibody and horse anti-mouse IgG as the secondary antibody (Vector Laboratories, Burlingame, CA) (7,28,90). The data presented represent a minimum of six spinal cord sections per mouse with no fewer than three mice per time point.…”

“…Although elegant work previously has been performed with regard to evaluating the functional role of CD8 ϩ T cells and viral replication within the CNS of JHMV-infected mice (7,62,80,83), it is likely that additional signaling molecules associated with CD8 ϩ T cells also contribute to the control of viral replication. NKG2D is a type II transmembrane glycoprotein that is expressed as a disulfide-linked homodimer on the surface of NK cells, CD8 ϩ T cells, and ␥␦ T cells in mice (20,41).…”

Vaccine-Induced Memory CD8+ T Cells Cannot Prevent Central Nervous System Virus Reactivation

“…CNS replication of the mouse hepatitis virus JHM strain (JHMV) 4 is controlled by CD8 ϩ T cells via perforin and IFN-␥-dependent mechanisms (19,20,21). A minimal role for Ab during acute infection was confirmed by efficient virus control in the CNS of B cell-deficient (J H D) mice (22).…”