THE CD8(-INFECTED CATS IS CHARACTERIZED BY REDUCED SURFACE EXPRESSIONOF THE CD8 BETA-CHAIN() CELL PHENOTYPE MEDIATING ANTIVIRAL ACTIVITY IN FELINE IMMUNODEFICIENCY VIRUS)

The acute stage of feline immunodeficiency virus (FIV) infection is ch aracterized by a CD8(+) anti-FIV response that parallels the appearanc e of a CDS' subpopulation with reduced expression of the beta chain (C D8 alpha(+)beta(lo)). The relationship between the CD8 alpha(+)beta(lo ) phenotype and CD8(+) anti-FIV activity was examined. Flow cytometric analysis of peripheral blood mononuclear cells with anti-CD8 beta cha in monoclonal antibody 117 revealed that the CD8 alpha(+)beta(lo) phen otype expanded throughout the asymptomatic infection, constituting 80% -90% of the CD8 beta(+) cells in long-term-infected cats. Purified CD8 alpha(+)beta(hi) and CD8 alpha(+)beta(lo) subpopulations were analyze d for anti-FIV activity in an acute infection assay. Anti-FIV activity resided principally in the CD8 alpha(+)beta(lo) population and was de monstrated in acute FIV infections, as well as in long-term asymptomat ic infections. These data suggest that a unique CD8 alpha(+)beta(lo) a nti-FIV phenotype arises early in infection and may play a major role in eliminating virus and maintaining the asymptomatic infection.