Progressive Expansion of an L-Selectin—Negative CD8 Cell with Anti—Feline Immunodeficiency Virus (FIV) Suppressor Function in the Circulation of FIV-Infected Cats

The acute stage of feline immunodeficiency virus (FIV) infection is characterized by the appearance of a major CD8 subpopulation with reduced expression of the CD8 β chain (CD8α+βlo). CD8 antiviral activity was subsequently shown to be mediated by the CD8α+βlo phenotype, which is the dominant CD8 phenotype in long-term infected cats. Two- and three-color flow cytometric analysis demonstrated that the CD8α+βlo subset is L-selectin negative (CD62L−) and has increased expression of CD44, CD49d, and CD18, consistent with an activation phenotype. The CD8α+βloCD62L− cells but not the CD8α+βhiCD62L+ cells demonstrated strong antiviral activity in the FIV acute-infection assay. The progressive expansion of the CD8α+βloCD62L− effector subset cells in FIV-infected cats parallels that seen in human immunodeficiency virus (HIV)—infected patients, suggesting that failure in homeostatic mechanisms regulating lymphocyte activation or trafficking (or both) may be a consequence of both HIV and FIV infections.