PMC

Age-related changes in percentage of the CD4 single-positive (SP) (a) and CD8 SP (b) T cells with memory phenotype over the 5-year study period. All values were compared by using the Duncan test. *, † and ‡ indicate significant differences (P < 0·05) within double-positive (DP)-High versus DP-Low, DP-High versus DP-Middle, and DP-Middle versus DP-Low, respectively.

Changes in percentage of the double-positive (DP) T-cell subset in 20 cynomolgus monkeys over the 5-year study period. Percentages of the DP T-cell subset are shown as x-fold change, compared with those obtained from the monkeys when 6 years of age. The bold line indicates the mean value among the 20 monkeys tested. The dashed horizontal line indicates no change, compared with those (1x) at 6 years of age.

Increase of peripheral double-positive (DP) T cells in cynomolgus monkeys at 6 years of age. (a) Flow cytometric analysis of CD4 and CD8 co-expression on peripheral blood lymphocytes (PBL). The results shown are representative of 20 monkeys. (b) The percentage of DP T cells in PBL of 20 monkeys at 6 years of age. Four monkeys had a significantly higher percentage (>5% in PBL) of DP T cells when compared with those of other 16 monkeys. The bars indicate the mean, and the P-value was obtained using the Student's t-test.

Age-related changes in each T cell subset – CD4 single positive (SP), CD8 SP and double-positive (DP) T cells – over the 5-year study period. (a) Although the percentage of each T-cell subset was variable, the percentage sum in the CD4 SP and DP T cells was essentially unchanged in each group during the 5-year study period. (b) In two monkeys of the DP-High group, a rapid increase was observed in the proportion of DP T cells over an 8-month time-period. Data shown represent the proportional changes of T-cell subsets (CD4 SP, CD8 SP and DP T cells), in total CD3⁺ cells, over 8 months. Values shown in the boxes represent the percentage of each subset.

Percentages of CD4 single-positive (SP) and CD8 SP T cells with memory phenotype in cynomolgus monkeys at 6 years of age. To evaluate the percentage of T cells with memory phenotype, the leucocytes isolated from 20 monkeys were stained with CD28-labelled fluorescein isothiocyanate (FITC) or CD29-FITC, CD4-labelled phycoerythrin (PE), and CD8-labelled R-phycoerythrin (RPE)-Cy5. In four monkeys with a higher percentage of double-positive (DP) T cells, the levels of memory CD4 SP (a) and CD8 SP (b) T cells were significantly higher than those of other monkeys. The P-value was obtained using the Student's t-test.