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

+ b lo subset is L-selectin negative (CD62L 2 ) and has increased expression of CD44, CD49d, and CD18, consistent with an activation phenotype. The CD8a + b lo CD62L 2 cells but not the CD8a + b hi CD62L + cells dem- onstrated strong antiviral activity in the FIV acute-infection assay. The progressive expansion of the CD8a + b lo CD62L 2 effector subset cells in FIV-infected cats parallels that seen in human immunodeficiency virus (HIV)-infected patients, suggesting that failure in homeostatic mech- anisms regulating lymphocyte activation or trafficking (or both) may be a consequence of both HIV and FIV infections. Feline immunodeficiency virus (FIV), similar to human im- munodeficiency virus (HIV), induces a CD8 T cell lymphocy- tosis during the acute stage of infection that persists throughout the asymptomatic stage of disease (1-3). In both FIV and HIV infections, CD8 lymphocytosis correlates with the emergence of CD8 cells that provide antiviral immunity through both cy- totoxic and virus-suppressive mechanisms (4-8). CD8 cells that mediate immunity through cytotoxic or sup- pressor mechanisms can be subdivided by differential expres- sion of surface markers. Landay et al. (9) demonstrated that HLA-DR and CD38 expression on CD8 lymphocytes cor- relates with high antiviral activity. However, the CD8 1