Reduced provirus burden and enhanced humoral immune function in AZT-treated SCID-feline mice inoculated with feline immunodeficiency virus.

The lack of a safe, economical murine lentivirus model for human immunodeficiency virus type 1 (HIV-1) infection of humans has hampered the preclinical evaluation of potential antiviral compounds, vaccines, and biological response modifiers. A small animal model that does not employ HIV-1 is needed to minimize risk of accidental human exposure, enhance efficient use of scarce experimental compounds, and reduce laboratory space necessary to conduct statistically significant in vivo trials. Feline immunodeficiency virus (FIV), an immunosuppressive lentivirus of domestic cats, has been used extensively as an animal model for the pathogenesis and therapy of human HIV-1 infection. Cats, however, are not amenable to large-scale efficacy trials because of their relatively large size, high cost, and limited degree of physiologic characterization, particularly with regard to drug metabolism. To adapt the feline immune system to a small laboratory animal host, severe combined immunodeficient mice (SCID mice) were engrafted with feline lymphoid tissues (forming the SCID-fe mouse) and inoculated with FIV. Two quantitative parameters, the incidence of provirus detection in feline tissue grafts and the level of feline IgG in plasma, were used to demonstrate the antiviral efficacy of 3'-azido-3'-deoxythymidine (AZT, azidothymidine, Retrovir, zidovudine) in the SCID-fe system. Of 17 SCID-fe mice inoculated with 7 x 10(6) peripheral blood mononuclear cells (PBMC) from an FIV-infected cat, eight had detectable FIV provirus in both the feline thymus and feline lymph node implants, as measured by polymerase chain reaction (PCR)/Southern blot analysis. Treatment of these mice with AZT at a dose of 125 mg kg-1 day-1 in drinking water beginning 1 day prior to FIV inoculation and continuing throughout the study interval prevented the dual detection of provirus in feline lymph node and thymus grafts of all mice tested. In a separate experiment, the level of spontaneous feline IgG production was quantified by ELISA 2 weeks after FIV inoculation with and without AZT treatment. Mean plasma feline IgG level of five SCID-fe mice inoculated with 10(3) TCID50 cell-free FIV was 2.23 mg ml-1. Mean feline IgG level of five mice inoculated with the same quantity of FIV and treated with AZT beginning 1 day prior to virus inoculation and continuing for 2 weeks thereafter was 14.98 mg ml-1. AZT significantly (P < 0.05) enhanced feline humoral immune function at a virus inoculum titer of 10(3) TCID50.(ABSTRACT TRUNCATED AT 400 WORDS)

Feline lymphoid tissues engrafted into scid mice maintain morphologic structure and produce feline immunoglobulin.

To adapt the feline immune system to a small laboratory animal host, severe combined immunodeficient (scid) mice were engrafted with neonatal feline lymphoid tissues, including lymph node, thymus, spleen, and bone marrow. Lymph node and thymus tissue were implanted subcutaneously within the mammary fat pad, and a single-cell suspension of spleen, thymus, and bone marrow was inoculated intraperitoneally (IP). Seven groups of mice (three mice per group) were engrafted on day 0, and members of one group were euthanatized weekly from 2 to 8 weeks after engraftment. For each mouse, graft morphology was evaluated by light microscopy, feline DNA was detected in peripheral blood by polymerase chain reaction (PCR) amplification of feline-specific DNA sequences, and serum IgG concentration was measured by ELISA. Ten of 13 feline grafts evaluated histologically between 3 and 8 weeks after engraftment contained large focal aggregates of lymphocytes bordered by plasma cells. Of 14 thymus grafts evaluated histologically during the same period, 5 were characterized by dense accumulations of small lymphocytes surrounding thymic epithelial cells. Two of these thymus grafts were indistinguishable from age-matched feline thymus. At 2 weeks after engraftment, feline lymph node and thymus contained extensive central necrosis bordered by a narrow zone of lymphocytes and small-caliber blood vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

Infection of the choroid plexus by feline immunodeficiency virus.

The human, simian, and feline immunodeficiency viruses rapidly penetrate into the brain and trigger an inflammatory process that can lead to significant neurologic disease. However, the mechanisms that permit efficient trafficking of macrophage-tropic and the more neurotoxic lymphocytotropic isolates are still poorly understood. One potential source of virus entry may be the blood-CSF barrier provided by the choroid plexus. Infected cells are often detected within the choroid plexus but it is unclear whether this reflects trafficking cells or infection of the large macrophage population within the choroidal stroma. To address this issue, we cultured fetal feline choroid plexus and evaluated the ability of feline immunodeficiency virus (FIV) to establish a primary infection. Significant provirus was detected in macrophage-enriched choroid plexus cultures as well as in the choroid plexus of cats infected in vivo. FIV p24 antigen production in vitro was very low but detectable. Addition of a feline T-cell line to macrophages inoculated with FIV resulted in a dense clustering of the T cells over macrophages with dendritic cell-like morphologies and a robust productive infection. The direct infection of choroid plexus macrophages with FIV, the efficient transfer of the infection to T cells indicate that the choroid plexus can be a highly efficient site of viral infection and perhaps trafficking of both macrophage-tropic and T-cell-tropic viruses into the CNS.

The CD8+ cell phenotype mediating antiviral activity in feline immunodeficiency virus-infected cats is characterized by reduced surface expression of the CD8 beta chain.

The acute stage of feline immunodeficiency virus (FIV) infection is characterized by a CD8+ anti-FIV response that parallels the appearance of a CD8+ subpopulation with reduced expression of the beta chain (CD8 alpha + beta lo). The relationship between the CD8 alpha + beta lo phenotype and CD8+ anti-FIV activity was examined. Flow cytometric analysis of peripheral blood mononuclear cells with anti-CD8 beta chain monoclonal antibody 117 revealed that the CD8 alpha + beta lo phenotype expanded throughout the asymptomatic infection, constituting 80%-90% of the CD8 beta + cells in long-term-infected cats. Purified CD8 alpha + beta hi and CD8 alpha + beta lo subpopulations were analyzed for anti-FIV activity in an acute infection assay. Anti-FIV activity resided principally in the CD8 alpha + beta lo population and was demonstrated in acute FIV infections, as well as in long-term asymptomatic infections. These data suggest that a unique CD8 alpha + beta lo anti-FIV phenotype arises early in infection and may play a major role in eliminating virus and maintaining the asymptomatic infection.

Progressive expansion of an L-selectin-negative CD8 cell with anti-feline immunodeficiency virus (FIV) suppressor function in the circulation of FIV-infected cats.

The acute stage of feline immunodeficiency virus (FIV) infection is characterized by the appearance of a major CD8 subpopulation with reduced expression of the CD8 beta chain (CD8alpha+betalo). CD8 antiviral activity was subsequently shown to be mediated by the CD8alpha+betalo phenotype, which is the dominant CD8 phenotype in long-term infected cats. Two- and three-color flow cytometric analysis demonstrated that the CD8alpha+betalo subset is L-selectin negative (CD62L-) and has increased expression of CD44, CD49d, and CD18, consistent with an activation phenotype. The CD8alpha+betaloCD62L- cells but not the CD8alpha+betahiCD62L+ cells demonstrated strong antiviral activity in the FIV acute-infection assay. The progressive expansion of the CD8alpha+betaloCD62L- effector subset cells in FIV-infected cats parallels that seen in human immunodeficiency virus (HIV)-infected patients, suggesting that failure in homeostatic mechanisms regulating lymphocyte activation or trafficking (or both) may be a consequence of both HIV and FIV infections.

Mucosally transmitted feline immunodeficiency virus induces a CD8+ antiviral response that correlates with reduction of cell-associated virus.

Intravaginal inoculation of cats with feline immunodeficiency virus (FIV) results in acute systemic infection accompanied by a strong CD8+ immune response that inhibits viral replication. CD8+ anti-FIV activity, revealed by increased FIV replication in peripheral blood mononuclear cells (PBMC) depleted of CD8+ lymphocytes, was detected by 6 weeks after inoculation and correlated with reduced PBMC-associated virus at 12, 16, and 32 weeks after inoculation. Some cats with strong CD8+ anti-FIV activity during acute infection did not seroconvert and yielded no evidence of FIV infection at later times. These data suggest that CD8+ immunity may play a major role in eliminating virus during primary transmucosal FIV infection and may down-regulate viral replication during asymptomatic infection.