In vitro replication and cytopathogenicity of the feline immunodeficiency virus for feline T4 thymic lymphoma 3201 cells.

Cytotoxic feline immunodeficiency virus (FIV) infection was established in feline T4 thymic lymphoma 3201 cells with the Petaluma isolate of the feline immunodeficiency virus (FIV-Petaluma). Mg2(+)-dependent, reverse transcriptase (Mg2+ RT) activity and FIV p24/28-positive cells were evident beginning at 18 days postinoculation (dpi). Cell death was observed beginning at 22 dpi, with a maximum of 40% dead (trypan blue dye exclusion at 26 dpi). This cytocidal change was not observed in cultured Crandell feline kidney fibroblasts similarly infected with FIV-Petaluma. The surviving cells grew out and a chronic FIV-producer cell line was established. The 3201 cell-derived FIV (FIV-3201) was far more virulent for FIV-naive feline 3201 cells, with FIV p24/28-positive cells and Mg2+ RT activity first detectable by 4-8 dpi and subsequent loss of cell viability detectable by 8-12 dpi. Maximum kill (40% dead) was observed at 16 dpi. Comparison between viral infectivity of FIV-Petaluma and FIV-3201 for FIV-naive 3201 cells showed an increase of 1 log10 tissue culture infectious doses (TCID50) by amplification/passage in 3201 cells. Cytologic and electron microscopic examination of 3201 cells in FIV-infected cultures showed frequent budding lentiviral particles. This lytic infection system opens the way to the routine detection, isolation, and quantitation of FIV from FIV-infected cats, to the large-scale propagation of the virus, and to a system for evaluation of the mechanisms of FIV lymphocytotoxicity and the development of therapies to counteract lentiviral cytopathicity.