Interferon Beta Contributes to Astrocyte Activation in the Brain following Reovirus Infection.

Reovirus encephalitis in mice was used as a model system to investigate astrocyte activation (astrogliosis) following viral infection of the brain. Reovirus infection resulted in astrogliosis, as evidenced by increased expression of glial fibrillary acidic protein (GFAP), and the upregulation of genes that have been previously associated with astrocyte activation. Astrocyte activation occurred in regions of the brain that are targeted by reovirus but extended beyond areas of active infection. Astrogliosis also occurred following reovirus infection of ex vivo brain slice cultures (BSCs), demonstrating that factors intrinsic to the brain are sufficient to activate astrocytes and that this process can occur in the absence of any contribution from the peripheral immune response. In agreement with previous reports, reovirus antigen did not colocalize with GFAP in infected brains, suggesting that reovirus does not infect astrocytes. Reovirus-infected neurons produce interferon beta (IFN-ß). IFN-ß treatment of primary astrocytes resulted in both the upregulation of GFAP and cytokines that are associated with astrocyte activation. In addition, the ability of media from reovirus-infected BSCs to activate primary astrocytes was blocked by anti-IFN-ß antibodies. These results suggest that IFN-ß, likely released from reovirus-infected neurons, results in the activation of astrocytes during reovirus encephalitis. In areas where infection and injury were pronounced, an absence of GFAP staining was consistent with activation-induced cell death as a mechanism of inflammation control. In support of this, activated Bak and cleaved caspase 3 were detected in astrocytes within reovirus-infected brains, indicating that activated astrocytes undergo apoptosis.IMPORTANCE Viral encephalitis is a significant cause of worldwide morbidity and mortality, and specific treatments are extremely limited. Virus infection of the brain triggers neuroinflammation; however, the role of neuroinflammation in the pathogenesis of viral encephalitis is unclear. Initial neuroinflammatory responses likely contribute to viral clearance, but prolonged exposure to proinflammatory cytokines released during neuroinflammation may be deleterious and contribute to neuronal death and tissue injury. Activation of astrocytes is a hallmark of neuroinflammation. Here, we show that reovirus infection of the brain results in the activation of astrocytes via an IFN-ß-mediated process and that these astrocytes later die by Bak-mediated apoptosis. A better understanding of neuroinflammatory responses during viral encephalitis may facilitate the development of new treatment strategies for these diseases.

The proapoptotic Bcl-2 protein Bax plays an important role in the pathogenesis of reovirus encephalitis.

Encephalitis induced by reovirus serotype 3 (T3) strains results from the apoptotic death of infected neurons. Extrinsic apoptotic signaling is activated in reovirus-infected neurons in vitro and in vivo, but the role of intrinsic apoptosis signaling during encephalitis is largely unknown. Bax plays a key role in intrinsic apoptotic signaling in neurons by allowing the release of mitochondrial cytochrome c. We found Bax activation and cytochrome c release in neurons following infection of neonatal mice with T3 reoviruses. Bax(-/-) mice infected with T3 Abney (T3A) have reduced central nervous system (CNS) tissue injury and decreased apoptosis, despite viral replication that is similar to that in wild-type (WT) Bax(+/+) mice. In contrast, in the heart, T3A-infected Bax(-/-) mice have viral growth, caspase activation, and injury comparable to those in WT mice, indicating that the role of Bax in pathogenesis is organ specific. Nonmyocarditic T3 Dearing (T3D)-infected Bax(-/-) mice had delayed disease and enhanced survival compared to WT mice. T3D-infected Bax(-/-) mice had significantly lower viral titers and levels of activated caspase 3 in the brain despite unaffected transneuronal spread of virus. Cytochrome c and Smac release occurred in some reovirus-infected neurons in the absence of Bax; however, this was clearly reduced compared to levels seen in Bax(+/+) wild-type mice, indicating that Bax is necessary for efficient activation of proapoptotic mitochondrial signaling in infected neurons. Our studies suggest that Bax is important for reovirus growth and pathogenesis in neurons and that the intrinsic pathway of apoptosis, mediated by Bax, is important for full expression of disease, CNS tissue injury, apoptosis, and viral growth in the CNS of reovirus-infected mice.

Anticyclic Citrullinated Peptide Antibodies 3.1 and Anti-CCP-IgA Are Associated with Increasing Age in Individuals Without Rheumatoid Arthritis.

OBJECTIVE: We investigated the association of age and anticyclic citrullinated peptide antibodies (anti-CCP) in subjects without rheumatoid arthritis (RA). METHODS: Serum was tested for anti-CCP3.1 (IgG/IgA) in 678 first-degree relatives (FDR) of patients with RA and 330 patients with osteoarthritis (OA). Individual isotypes (anti-CCP-IgA and anti-CCP-IgG) were also tested in all FDR. RESULTS: In FDR, increasing age was significantly associated with positivity for anti-CCP3.1 (per year, OR 1.03) and anti-CCP-IgA (per year, OR 1.05) but not anti-CCP-IgG. In FDR and OA subjects, anti-CCP3.1 prevalence was significantly increased after age 50 years. CONCLUSION: Increasing age in individuals without RA should be considered in the interpretation of anti-CCP3.1 positivity.