Figure 4.

The four memory-phenotype (MP) subpopulations are maintained via T-cell receptor (TCR) and CD28 signaling. (A–D) CD127^lo MP subsets represent cell populations that have recently received TCR signaling. Representative histograms display (A) TCRβ, CD3, (B) CD5, (C) CD69, and (D) GFP expression in the indicated MP subpopulations from Nur77-GFP reporter mice, while the bar graphs indicate (C) the frequency (mean ± SD) of CD69⁺ and (D) the mean fluorescence intensity (MFI) (mean ± SD) of GFP among the MP subpopulations (n = 5 mice). Filled histograms show negative control staining, whereas black and open histograms display naïve CD4⁺ T cells. (E, F) TCR signaling is essential for proliferation and dynamic equilibrium of MP subpopulations. CD4-CreERT2 TCRα^flox mice received tamoxifen (TMX) and were analyzed 10 days later. Bar graphs indicating the frequency (mean ± SD) of (E) Ki67⁺ cells among both TCRβ⁺ and TCRβ^neg fractions from each MP subset and (F) the indicated subpopulations among the TCRβ⁺ or TCRβ^neg MP cells are depicted (n = 5 mice). (G, H) CD28 signals are critical for optimal maintenance of MP subpopulations. Mice received CTLA4-Ig and were analyzed 10 days later. The bar graphs show the frequency (mean ± SD) of (G) Ki67⁺ cells among the indicated MP subpopulations from each group and (H) the indicated subsets among total MP T lymphocytes (n = 5 mice). Data are representative of 2 independent experiments. Statistically significant differences are indicated as *p < 0.05, **p < 0.01, and ***p < 0.001.