EVIDENCE FOR CD8(+) ANTIVIRAL ACTIVITY IN CATS INFECTED WITH FELINE IMMUNODEFICIENCY VIRUS

Human immunodeficiency virus (HIV) causes a long, asymptomatic infecti on characterized by normal to elevated numbers of circulating CD8(+) c ells and a progressive decline in CD4(+) cells. It has been speculated that HIV-specific antiviral activity driven by CD8(+) T cells may con trol viral replication during this period and maintain the clinically asymptomatic stage of disease. The disease induced in cats by feline i mmunodeficiency virus (FIV) is similar to HIV in that it is characteri zed by a long asymptomatic stage with a progressive decline in CD4(+) cells, culminating in AIDS. In the present study, we demonstrate that FIV is more readily isolated from CD8(+) T-cell-depleted peripheral bl ood mononuclear cells (PBMC) of FIV-infected cats than from unfraction ated PBMC cultures. In addition, CD8(+) cells isolated from FIV-positi ve cats demonstrating anti-FIV activity in PBMC cultures inhibit FIV i nfection of FCD4E cells in vitro. Anti-FIV activity is not found in FI V-negative cats and is not characteristic of cats acutely infected wit h FIV but is present in the majority of chronically infected, clinical ly asymptomatic and symptomatic cats. Decreases in plasma and cell-ass ociated viremia during the acute-stage FIV infection appears to preced e the appearance of CD8(+) anti-FIV cells in the circulation. In summa ry, this study demonstrates a population(s) of CD8(+) T cells in chron ically FIV-infected cats capable of suppressing FIV replication in cul tured PBMC. The significance of anti-FIV CD8(+) cells in the immunopat hogenesis of the infection and disease progression has yet to be deter mined.