MOLECULARLY CLONED FELINE IMMUNODEFICIENCY VIRUS NCSU1 JSY3 INDUCES IMMUNODEFICIENCY IN SPECIFIC-PATHOGEN-FREE CATS

A full-length feline immunodeficiency virus NCSU1 (FIV-NCSU1) genome ( JSY3) was cloned directly from FIV-NCSU1-infected feline CD4+ lymphocy te (FCD4E) genomic DNA and identified by PCR amplification with 5' lon g terminal repeat, gag, env, and 3' long terminal repeat primer sets. Supernatant from FCD4E cells cocultured with JSY3-transfected Crandell feline kidney (CrFK) cells was used as an inoculum. Cell-free JSY3 vi rus was cytopathogenic for FCD4E lymphocytes but did not infect CrFK c ells in vitro. To determine in vivo infectivity and pathogenesis, six young adult specific-pathogen-free cats were inoculated with cell-free JSY3 virus. Provirus was detected at 2 weeks postinfection (p.i.) and was still detectable at 25 weeks p.i. as determined by gag region PCR -Southern blot analysis of peripheral blood mononuclear cell lysates. Infectious virus was recovered from peripheral blood mononuclear cells at 6 and 25 weeks p.i., and an antibody response to FIV was detected by 4 weeks. In the acute phase of infection, JSY3 provirus was found o nly in the CD4(+) lymphocyte subset; however, by 14 weeks p.i., the gr eatest provirus burden was detected in B lymphocytes. All six cats wer e panlymphopenic at 2 weeks p.i., CD4(+)/CD8(+) ratios were inverted b y 6 weeks p.i., and five of the six cats developed lymphadenopathy by 10 weeks p.i. To determine if the JSY3 molecular clone caused immunode ficiency similar to that of the parental wild-type FIV-NCSU1, the cats were challenged with the low-virulence ME49 strain of Toxoplasma gond ii at 29 weeks p.i. Five of six cats developed clinical signs consiste nt with generalized toxoplasmosis, and three of six cats developed acu te respiratory distress and required euthanasia. Histopathologic exami nation of the severely affected cats revealed generalized inflammatory reactions and the presence of T. gondii tachyzoites in multiple tissu es. None of the six age- and sex-matched specific-pathogen-free cats i noculated with only T. gondii developed clinical disease. Our results suggest that the pathogenesis of the molecularly cloned NCSU1 JSY3 is similar to that of wild-type FIV-NCSU1.