Real time multi-photon imaging reveals coordination between thymocyte development, location and migration through intrathymic microenvironments (85.6)

Abstract

Abstract As they develop, CD4-CD8- (DN) thymocytes are found progressively from the corticomedullary junction towards the capsule. Following beta selection, CD4 and CD8 are expressed, generating double positive (DP) thymocytes that are found throughout the cortex. If a DP thymoycte expresses T cell receptor (TCR) and passes positive-selection, it becomes a single positive (SP) thymocyte, which is located in the medulla. Static images have revealed this intrathymic localization, suggesting a model in which DN thymocytes migrate directionally towards the capsule, while DP thymocytes move towards the medulla, which they enter as SP thymocytes. Using multi-photon imaging of thymocyte subsets in thick thymic slices, we directly test this model. Using thymuses expressing EGFP, we identify the precise microenvironments in which thymocyte subsets are localized. For the first time, we now image within the thymic medulla. We find that DN and DP thymocytes migrate without directional bias throughout the cortex, but DP velocities are influenced by cortical micorenvironmental cues. Interestingly, only SP thymocytes enter the medulla, where they migrate very rapidly. SPs also migrate rapidly in the cortex, where their movement is biased towards the medulla. Importantly, medullary entry is strictly dependent on G-protein-coupled receptor activity, though CCR7 signaling cannot entirely account for this requirement. L.I.R.E is a Leukemia and Lymphoma Society Special Fellow