PRIMARY STAGE OF FELINE IMMUNODEFICIENCY VIRUS-INFECTION - VIRAL DISSEMINATION AND CELLULAR TARGETS

The objective of this study was to identify cellular and organ targets of acute feline immunodeficiency virus (FIV) infection in vivo. Tissu es of FIV-infected cats were studied at eight time points during the f irst 3 months after experimental infection. FIV nucleic acids were fir st detected by in situ hybridization 21 days after infection, approxim ately 1.5 weeks after lymph node enlargement was first observed and 3 weeks before the primary acute flu-like illness. The majority of FIV-i nfected cells were present in lymphoid organs, though low numbers of i nfected cells were noted in nonlymphoid organs as well. Germinal cente rs harbored many of the FIV-infected cells within lymphoid tissues. Th e thymic cortex was also a major site of early infection. Combined in situ hybridization and immunohistochemistry revealed that T lymphocyte s were the primary target of early FIV infection in tissues of cats be fore the onset of clinical signs of acute illness. An unidentified pop ulation of mononuclear sells and a few macrophages were also infected. During the ensuing acute flu like illness, the proportion of FIV-infe cted macrophages in tissues increased dramatically. This early shift i n the predominant cellular localization of FIV from T lymphocytes to m acrophages may be important for establishing viral persistence.