Gabriel I. Parra

Target-Dependent B7-H1 Regulation Contributes to Clearance of Central Nervous Sysyem Infection and Dampens Morbidity

The neurotropic coronavirus JHM strain of mouse hepatitis virus persists in oligodendroglia despite the presence of virus-specific CD8 T cells. Expression of programmed death 1 (PD-1) and B7-H1 were studied during acute and persistent infection to examine whether this negative regulatory mechanism contributes to CNS viral persistence. The majority of CNS-infiltrating CD8 T cells expressed PD-1, with the highest levels on virus-specific CD8 T cells. Moreover, despite control of infectious virus, CD8 T cells within the CNS of persistently infected mice maintained high PD-1 expression. Analysis of virus-susceptible target cells in vivo revealed that B7-H1 expression was regulated in a cell type-dependent manner. Oligodendroglia and microglia up-regulated B7-H1 following infection; however, although B7-H1 expression on oligodendroglia was prominent and sustained, it was significantly reduced and transient on microglia. Infection of mice deficient in the IFN-γ or IFN-α/β receptor demonstrated that B7-H1 expression on oligodendroglia is predominantly regulated by IFN-γ. Ab blockade of B7-H1 on oligodendroglia in vitro enhanced IFN-γ secretion by virus-specific CD8 T cells. More efficient virus control within the CNS of B7-H1-deficient mice confirmed inhibition of CD8 T cell function in vivo. Nevertheless, the absence of B7-H1 significantly increased morbidity without altering demyelination. These data are the first to demonstrate glia cell type-dependent B7-H1 regulation in vivo, resulting in adverse effects on antiviral CD8 T cell function. However, the beneficial role of PD-1:B7-H1 interactions in limiting morbidity highlights the need to evaluate tissue-specific intervention strategies.

IFN-γ Signaling to Astrocytes Protects from Autoimmune Mediated Neurological Disability

Demyelination and axonal degeneration are determinants of progressive neurological disability in patients with multiple sclerosis (MS). Cells resident within the central nervous system (CNS) are active participants in development, progression and subsequent control of autoimmune disease; however, their individual contributions are not well understood. Astrocytes, the most abundant CNS cell type, are highly sensitive to environmental cues and are implicated in both detrimental and protective outcomes during autoimmune demyelination. Experimental autoimmune encephalomyelitis (EAE) was induced in transgenic mice expressing signaling defective dominant-negative interferon gamma (IFN-γ) receptors on astrocytes to determine the influence of inflammation on astrocyte activity. Inhibition of IFN-γ signaling to astrocytes did not influence disease incidence, onset, initial progression of symptoms, blood brain barrier (BBB) integrity or the composition of the acute CNS inflammatory response. Nevertheless, increased demyelination at peak acute disease in the absence of IFN-γ signaling to astrocytes correlated with sustained clinical symptoms. Following peak disease, diminished clinical remission, increased mortality and sustained astrocyte activation within the gray matter demonstrate a critical role of IFN-γ signaling to astrocytes in neuroprotection. Diminished disease remission was associated with escalating demyelination, axonal degeneration and sustained inflammation. The CNS infiltrating leukocyte composition was not altered; however, decreased IL-10 and IL-27 correlated with sustained disease. These data indicate that astrocytes play a critical role in limiting CNS autoimmune disease dependent upon a neuroprotective signaling pathway mediated by engagement of IFN-γ receptors.

Shifting Hierarchies of Interleukin-10-Producing T Cell Populations in the Central Nervous System during Acute and Persistent Viral Encephalomyelitis

ABSTRACT Interleukin-10 (IL-10) mRNA is rapidly upregulated in the central nervous system (CNS) following infection with neurotropic coronavirus and remains elevated during persistent infection. Infection of transgenic IL-10/green fluorescent protein (GFP) reporter mice revealed that CNS-infiltrating T cells were the major source of IL-10, with minimal IL-10 production by macrophages and resident microglia. The proportions of IL-10-producing cells were initially similar in CD8+ and CD4+ T cells but diminished rapidly in CD8+ T cells as the virus was controlled. Overall, the majority of IL-10-producing CD8+ T cells were specific for the immunodominant major histocompatibility complex (MHC) class I epitope. Unlike CD8+ T cells, a large proportion of CD4+ T cells within the CNS retained IL-10 production throughout persistence. Furthermore, elevated frequencies of IL-10-producing CD4+ T cells in the spinal cord supported preferential maintenance of IL-10 production at the site of viral persistence and tissue damage. IL-10 was produced primarily by the CD25+ CD4+ T cell subset during acute infection but prevailed in CD25− CD4+ T cells during the transition to persistent infection and thereafter. Overall, these data demonstrate significant fluidity in the T-cell-mediated IL-10 response during viral encephalitis and persistence. While IL-10 production by CD8+ T cells was limited primarily to the time of acute effector function, CD4+ T cells continued to produce IL-10 throughout infection. Moreover, a shift from predominant IL-10 production by CD25+ CD4+ T cells to CD25− CD4+ T cells suggests that a transition to nonclassical regulatory T cells precedes and is retained during CNS viral persistence.

Sequential gastroenteritis episodes caused by 2 norovirus genotypes.

We investigated sequential episodes of acute norovirus gastroenteritis in a young child within an 11-month period. The infections were caused by 2 distinct genotypes (GII.4 and GII.6). Failure to achieve cross-protective immunity was linked to absence of an enduring and cross-reactive mucosal immune response, a critical consideration for vaccine design.

Gamma interferon signaling in oligodendrocytes is critical for protection from neurotropic coronavirus infection.

ABSTRACT Neurotropic coronavirus induces acute encephalomyelitis and demyelination in mice. Infection of BALB/c (H-2d) mice expressing a dominant negative gamma interferon (IFN-γ) receptor specifically in oligodendrocytes was examined to determine the influence of IFN-γ signaling on pathogenesis. Inhibition of IFN-γ signaling in oligodendrocytes increased viral load, infection of oligodendrocytes, oligodendrocyte loss, demyelination, and axonal damage resulting in increased mortality. IFN-γ levels and the inflammatory response were not altered, although the level of tumor necrosis factor (TNF) mRNA was increased. These data indicate that IFN-γ signaling by oligodendroglia reduces viral replication but affects both demyelination and tissue destruction in a host-specific manner.

IL-15 independent maintenance of virus-specific CD8+ T cells in the CNS during chronic infection

n Abstractn n The role of IL-15 in T cell survival was examined during chronic CNS coronavirus infection. Similar numbers of virus-specific CD8+ T cells were retained in the CNS of IL-15−/− and wt mice, consistent with loss of IL-2/15 receptor (CD122) expression. IL-15 deficiency also had no affect on IL-7 receptor (CD127) expression, Bcl-2 upregulation, granzyme B expression, or IFN-γ secretion in CNS persisting CD8+ T cells. Furthermore, CD8+ T cell division in the CNS was reduced compared to spleen. CD8+ T cells in the persistently infected CNS are thus characterized by IL-15 independent, low level proliferation and an activated/memory phenotype.n n