Fig 6. Frequency and distribution of SIV-specific CD8⁺ peripheral blood T cells on the day of superinfection challenge with respect to protection status.

Cell populations were determined by multi-parametric flow cytometry following stimulation of PBMC separately with SIV-Gag, Rev and Tat peptide pools. Background responses detected in medium alone control samples were subtracted for every combination of cytokines and a cut-off of >0.01% after background subtraction was used as the threshold for positive reactivity (dashed line). Frequencies were derived by addition of results for Gag, Rev and Tat. Box plots show the 25^th and 75^th percentiles and median (solid line) and mean (dotted line) for each cytokine combination (a & c). Statistically significant differences are highlighted by blue boxes. Proportionate functionality for each macaque (b & d) is shown as a pie chart, with quadruple positivity shown in black and triple to mono positivity shown as shades of grey. Arcs show the combination of cytokine reactivities.