Feline CD8+ T cell non-cytolytic anti-feline immunodeficiency virus activity mediated by a soluble factor(s)

Feline immunodeficiency virus (FIV) is more readily isolated from CD8(+) T cell-depleted peripheral blood mononuclear cells (PBMC) of FIV-infected cats than from unfractionated PBMC cultures. However, it is not known whether feline CD8(+) T cells downregulate FIV expression by direct interaction with FIV-infected cells or via a soluble mediator. Furthermore, it is not known whether this anti-FIV activity involves a lyric or non-lytic mechanism. In the present study, we demonstrated that autologous and allogeneic CD8(+) T cells from asymptomatic FIV-infected cats inhibited the replication of FIV in CD8(+) T cell-depleted PBMC cultures in a dose-dependent manner. The inhibitory effect was mediated by a non-lytic mechanism, and was not dependent on direct cell-to-cell contact: an inhibitory effect was exerted by CD8(+) T cells across a semi-permeable membrane, and an inhibitory activity was also present in cell-free supernatants from CD8(+) T cells. These results suggest that this suppressive effect is mediated, at least in part, by soluble factors produced by CD8(+) T cells.