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 I weeks postinoculation. Virus was isolated from CD4(+), CD8(+), and B cells in vitro, and reverse transcriptase PCR demonstrated that all subsets contained viral RNA in vivo and therefore are productive reservoirs for FIV.