Expansion of CD8α+β- cells in cats infected with feline immunodeficiency virus

CD8(+) lymphocytes have been subdivided into CD8 alpha beta and CD8 alpha alpha populations in the peripheral blood lymphocytes (PBL) of humans and in several animal species but have not yet been investigated in cats. Feline immunodeficiency virus (FIV) causes progressive immunological disorders similar to human AIDS. In this study, we analysed CD8(+) cells in PBL of FIV-infected or uninfected cats by two-colour Row cytometric analysis. In specific pathogen-free adult cats, feline CD8 alpha(+)beta(high) cells were observed but CD8 alpha(+)beta(-) cells were not found in significant numbers. On the other hand, not only CD8 alpha(+)beta(high) but also CD8 alpha(+)beta(-) and CD8 alpha(+)beta(low) cell populations were observed in cats chronically infected with FIV. The expansion of the CD8 beta(low) or CD8 beta(-) subpopulations resulted in the apparent differences in CD4/CD8 ratios depending on the anti-CD8 MAb used. These findings suggest a need to reconsider the CD4/CD8 ratio in studies of FIV infection. Furthermore, we found that the CD8 alpha(+)beta(-) cell population expressed CD5 at a low level.