Feline immunodeficiency virus: quantification in peripheral blood mononuclear cells and isolation from plasma of infected cats

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Abstract
The titer of feline immunodeficiency virus in peripheral blood mononuclear cells (PBMC) and the presence of infectious virus in plasma was investigated over 20 week period in 8 experimentally infected cats, 3 uninfected cats and 2 naturally infected cats by end point dilution cultures using a feline T-lymphoblastoid cell line (MYA-1). FIV was isolated from PBMC of all infected cats, but not from the uninfected cats. FIV was also isolated consistently from 100 µl plasma from most of the experimentally infected cats, but not from the 2 naturally infected cats. The virus titer in PBMCs in both experimentally and naturally infected cats was comparatively high, ranging from 10 TCID/106 PBMC to 14,286 TCID/106 PBMC. The titers in PBMC of individual cats remained unchanged or varied only slightly over the 20 week period. In contrast, the titers varied substantially between cats, with significantly higher titers in the youngest litter (4 cats) than in the oldest litter (3 cats). This suggests that there is an age-related factor influencing the level of PBMC virus titers in experimental infection with FIV. A similar age-related susceptibility has been shown with feline leukemia virus. More importantly, the sustained titers in the experimentally infected cats bear close resemblance to infection of children with human immunodeficiency virus. These data reinforce suggestions that age and immune maturity have a fundamental influence on PBMC and plasma titers in lentivirus infections.