Invitro 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). Mg 2+ -dependent, reverse transcriptase (Mg 2+ 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 Crandall 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 Mg 2+ 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 log 10 tissue culture infectious doses (TCID 50 ) 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.