Persistently inverted CD4/CD8 ratio despite undetectable plasma viral RNA. The CD4/CD8 T cell ratio for each FIV-infected and uninfected control cat is plotted as a function of time (a). Cumulative data from each of the 2 uninfected control cats are plotted as thick grey lines while data from the 4 individual FIV-infected cats are plotted as solid black lines (165), medium-dashed lines (184), short-dashed lines (186) and dotted lines (187). The cumulative mean CD4/CD8 T-cell ratio for FIV-infected cats (black bar) was derived from all individual CD4/CD8 T-cell ratios obtained from 2 weeks to 112 weeks PI and compared to the ratio for the mock-infected control cats (grey bar). Significance is shown using p value with * p = .0001 (b). Cumulative means for the absolute number of CD4+ and CD8+ T cells for FIV-infected cats were compared to values for uninfected control cats. Statistical significance is marked by an asterisk (*) and for this analysis p = .0017. Error bars denote standard deviation (c). Plasma viral RNA copy numbers based on a FIV gag-based real-time PCR assay are plotted for each FIV-infected cat: circle (cat 165), diamond (184), square (187) and triangle (186) (d). Assay detection threshold is approximately 80 copies viral RNA per ml.