Highly pathogenic avian influenza viruses do not inhibit interferon synthesis in infected chickens but can override the interferon-induced antiviral state

From infection studies with cultured chicken cells and experimental mammalian hosts, it is well known that influenza viruses use the nonstructural protein 1 (NS1) to suppress the synthesis of interferon (IFN). However, our current knowledge regarding the in vivo role of virus-encoded NS1 in chickens is much more limited. Here, we report that highly pathogenic avian influenza viruses of subtypes H5N1 and H7N7 lacking fully functional NS1 genes were attenuated in 5-week-old chickens. Surprisingly, in diseased birds infected with NS1 mutants, the IFN levels were not higher than in diseased birds infected with wild-type virus, suggesting that NS1 cannot suppress IFN gene expression in at least one cell population of infected chickens that produces large amounts of the cytokine in vivo. To address the question of why influenza viruses are highly pathogenic in chickens although they strongly activate the innate immune system, we determined whether recombinant chicken alpha interferon (IFN-α) can inhibit the growth of highly pathogenic avian influenza viruses in cultured chicken cells and whether it can ameliorate virus-induced disease in 5-week-old birds. We found that IFN treatment failed to confer substantial protection against challenge with highly pathogenic viruses, although it was effective against viruses with low pathogenic potential. Taken together, our data demonstrate that preventing the synthesis of IFN is not the primary role of the viral NS1 protein during infection of chickens. Our results further suggest that virus-induced IFN does not contribute substantially to resistance of chickens against highly pathogenic influenza viruses.     

Molecular cloning and expression of rat interferon-γ

The nueclotide sequence data reported in this paper have been submitted to the EMBL nucleotide databse and have been assigned the accession number X86972     

Changes of the organotypic retinal organization in Borna virus-infected Lewis rats

Retinae of Borna disease virus (BDV)-infected Lewis rats were investigated with emphasis on long-term changes in organotypic tissue organization and glia-neuron relationship. Virus inoculation was attained via intracerebral BDV injection. Following survival times ranging between two and eight months, the retinal thickness was reduced up to one third of that of controls. Photoreceptor segments were completely extinguished and the number of neurons was dramatically reduced. The typical laminar organization of the retina was largely dissolved. Electron microscopy revealed severe spongy degeneration. Large numbers of activated microglia and macrophages were found, both cell types performing very active phagocytosis. The microglial cells expressed an extraordinary phenotype as characterized by large numbers of processes, with some of them penetrating the endfeet of Müller cells and others establishing highly complex interdigitations with vacuolized swellings and endings of neuronal processes. Müller cells were not reduced in number but displayed clear indications of gliosis such as alterations in the immunoreactivity for filament proteins and glutamine synthetase, significantly thickened stem processes, and an altered pattern of K⁺ currents in patch-clamp recordings. These findings demonstrate for the first time long-term neuron-glia interactions in the retina of BDV-infected rats. Moreover, the data contribute to our knowledge on structural and functional alterations accompanying persisting virus infection in the central nervous system.     

Feline immunodeficiency virus infection phenotypically and functionally activates immunosuppressive CD4+CD25+ T regulatory cells

Disease progression of feline immunodeficiency virus (FIV) infection is characterized by up-regulation of B7.1 and B7.2 costimulatory molecules and their ligand CTLA4 on CD4(+) and CD8(+) T cells. The CD4(+)CTLA4(+)B7(+) phenotype described in FIV(+) cats is reminiscent of CD4(+)CD25(+)CTLA4(+) cells, a phenotype described for immunosuppressive T regulatory (Treg) cells. In the present study, we describe the phenotypic and functional characteristics of CD4(+)CD25(+) T cells in PBMC and lymph nodes (LN) of FIV(+) and control cats. Similar to Treg cells, feline CD4(+)CD25(+) but not CD4(+)CD25(-) T cells directly isolated from LN of FIV(+) cats do not produce IL-2 and fail to proliferate in response to mitogen stimulation. Unstimulated CD4(+)CD25(+) T cells from FIV(+) cats significantly suppress the proliferative response and the IL-2 production of Con A-stimulated autologous CD4(+)CD25(-) T cells compared with unstimulated CD4(+)CD25(+) T cells from FIV(-) cats. Flow-cytometric analysis confirmed the apparent activation phenotype of the CD4(+)CD25(+) cells in LN of chronically FIV(+) cats, because these cells showed significant up-regulation of expression of costimulatory molecules B7.1, B7.2, and CTLA4. These FIV-activated, anergic, immunosuppressive CD25(+)CTLA4(+)B7(+)CD4(+) Treg-like cells may contribute to the progressive loss of T cell immune function that is characteristic of FIV infection.     

A single amino acid substitution in the transmembrane envelope glycoprotein of feline immunodeficiency virus alters cellular tropism.

The cellular tropism of the feline immunodeficiency virus (FIV) is affected by changes in variable region 3 (V3) of the surface (SU) envelope glycoprotein (Verschoor, E. J., et al., J. Virol. 69:4752-4757, 1995). By using high-dose DNA transfection, an FIV molecular clone with a non-CRFK-tropic V3 acquired the ability to replicate in CRFK cells. A single point mutation from a methionine to a threonine in the ectodomain of its transmembrane (TM) envelope glycoprotein was responsible for this change in viral tropism. This substitution is located in the putative SU interactive region, between the fusion peptide and the membrane-spanning region. Our results show that this region of the TM envelope glycoprotein constitutes an additional determinant for cell tropism.