T cell-intrinsic S1PR1 regulates endogenous effector T-cell egress dynamics from lymph nodes during infection

Viral clearance requires effector T-cell egress from the draining lymph node (dLN). The mechanisms that regulate the complex process of effector T-cell egress from the dLN after infection are poorly understood. Here, we visualized endogenous pathogen-specific effector T-cell migration within, and from, the dLN. We used an inducible mouse model with a temporally disrupted sphingosine-1-phosphate receptor-1 (S1PR1) gene specifically in endogenous effector T cells. Early after infection, WT and S1PR1^-/- effector T cells localized exclusively within the paracortex. This localization in the paracortex by CD8 T cells was followed by intranodal migration by both WT and S1PR1^-/- T cells to positions adjacent to both cortical and medullary lymphatic sinuses where the T cells exhibited intense probing behavior. However, in contrast to WT, S1PR1^-/- effector T cells failed to enter the sinuses. We demonstrate that, even when LN retention signals such as CC chemokine receptor 7 (CCR7) are down-regulated, T cell intrinsic S1PR1 is the master regulator of effector T-cell emigration from the dLN.