Figure 5. Division history, CD62L expression, and memory formation in vivo.

The dynamics of the T cell response to infection were tracked from day 4 out to day 53 post-infection. Memory formation was studied by measuring the proportion of OT-1 cells at the peak that remained at day 53 post-infection. Survival of total OT-1 cells is positively correlated with adoptive transfer frequency (A) (Spearman’s tied rank correlation test), indicating that higher transfer amounts lead to better memory formation. This may have occurred because these cells underwent fewer divisions (were ‘younger’) or because a higher proportion of these cells were CD62L^high. Both division number (B) and CD62L expression (C) are significantly correlated with survival (Spearman’s rank correlation test). The average survival of the CD62L^high population (mean survival = 27.01%) was significantly higher than the CD62L^low population (mean survival = 6.25%, p < 0.0001 paired t-test), regardless of the adoptive transfer amount (D, E). When the CD62L^high and CD62L^low populations were analyzed separately, the survival of the CD62L^high population was not significantly correlated with adoptive transfer amount. However, there was a significant positive correlation between the survival of the CD62L^low population and adoptive transfer amount (p = 0.04, r = 0.57 Spearman tied-rank correlation) (D). There was also a trend towards reduced survival of CD62L^low cells that had divided more times (E), although this was not significant (p=0.08).