Proviral burden and infection kinetics of feline immunodeficiency virus in lymphocyte subsets of blood and lymph node

Feline immunodeficiency virus (FIV) is similar to human immunodeficiency virus type 1 virologically and induces a clinical syndrome in cats comparable to human immunodeficiency virus type 1 syndrome in humans. To determine the lymphoid target cells of FIV, populations of CD4 ⁺ lymphocytes, CD8 ⁺ lymphocytes, and CD21 ⁺ lymphocytes (B cells) were enriched to more than 96.5% purity and then analyzed for FIV provirus by semiquantitative DNA amplification. We found FIV provirus in CD4 ⁺, CD8 ⁺, and B lymphocytes. In cats infected for <4 months, proviral burden was greatest in CD4 ⁺ cells, followed by B cells and then by CD8 ⁺ cells. In cats infected for more than 5 years, proviral burden was greatest in B cells, followed by CD4 ⁺ cells and then by CD8 ⁺ cells. The total proviral burden was >1 log ₁₀ higher in acutely infected cats than in chronically infected cats, primarily because of a higher level of CD4 ⁺ infection in the acutely infected cats. A comparison of proviral loads in mesenteric lymph node and peripheral blood mononuclear cells in acutely or chronically infected cats revealed no significant difference. A kinetics study of FIV infection demonstrated that all lymphocyte subpopulations were infected by 4 weeks postinoculation. Virus was isolated from CD4 ⁺, CD8 ⁺, and B cells in vitro, and reverse transcriptase PER demonstrated that all subsets contained viral RNA in vivo and therefore are productive reservoirs for FIV.