The recombinant vaccinia virus gene product, B18R, neutralizes interferon alpha and alleviates histopathological complications in an HIV encephalitis mouse model

Abstract

Interferon-alpha (IFN-α) has been identified as a neurotoxin that plays a prominent role in human immunodeficiency virus (HIV)-associated neurocognitive disorders and HIV encephalitis (HIVE) pathology. IFN-α is associated with cognitive dysfunction in other inflammatory diseases where IFN-α is upregulated. Trials of monoclonal anti-IFN-α antibodies have been generally disappointing possibly due to high specificity to limited IFN-α subtypes and low affinity. We investigated a novel IFN-α inhibitor, B18R, in an HIVE/severe combined immunodeficiency (SCID) mouse model. Immunostaining for B18R in systemically treated HIVE/SCID mice suggested the ability of B18R to cross the blood-brain barrier (BBB). Real-time PCR indicated that B18R treatment resulted in a decrease in gene expression associated with IFN-α signaling in the brain. Mice treated with B18R were found to have decreased mouse mononuclear phagocytes and significant retention of neuronal arborization compared to untreated HIVE/SCID mice. Increased mononuclear phagocytes and decreased neuronal arborization are key features of HIVE. These results suggest that B18R crosses the BBB, blocks IFN-α signaling, and it prevents key features of HIVE pathology. These data suggest that the high affinity and broad IFN-α subtype specificity of B18R make it a viable alternative to monoclonal antibodies for the inhibition of IFN-α in the immune-suppressed environment.

FIG. 1.

Immunohistochemistry staining for B18R in mouse human immunodeficiency virus (HIV)-infected brain tissue in B18R-treated and untreated groups (A). Arrows indicate positive B18R staining on cells within the brain. Densitometry values (B) of B18R in brain sections of mice inoculated with HIV-infected human monocyte-derived macrophages (MDMs) and treated with saline (HIV-Saline; n=8) or B18R (HIV-B18R; n=8) (***P<0.001).

FIG. 2.

Real-time RT-PCR analysis of interferon stimulated genes (ISGs) [ISG15, IFN-alpha response gene 15 (Ifrg15), and IFN-alpha 4 gene (IFNA4)] mRNA in control (mice inoculated with uninfected human MDMs and treated with saline; n=8), HIV-Saline (mice inoculated with HIV-infected human MDMs and treated with saline; n=8), and HIV-B18R (mice inoculated with HIV-infected human MDMs and treated with B18R; n=8) (*P<0.05, **P<0.01).

FIG. 3.

Densitometry values of astrogliosis, microgliosis, and dendritic arborization in all mice. Astrocytes [mouse glial fibrillary acidic protein (GFAP)] expression was slightly decreased in HIV-B18R mice compared with HIV (A) (***P<0.001). Mice treated with B18R had significantly less staining for mouse macrophages and microglia (mouse CD45) compared with HIV mice (B) (*P<0.05, **P<0.01, ***P<0.001). B18R-treated mice were significantly protected against reduction in dendritic arborization [mouse microtubule associated protein-2 (MAP2)] compared to HIV mice (C) (*P<0.05).