In: Biology
CXCR4, CCR7 and CCR9 are all expressed by T-lymphoid progenitors and involved in the migration of developing thymocytes through different regions of the thymus. Crosstalk between these receptors and developmental receptors (the T cell receptor (TCR) and pre-TCR) regulates both thymocyte migration and thymocyte development.
Thymocyte emigration is precisely timed to occur only after maturation is completed and after thymocytes are screened by negative selection to remove overtly autoreactive cells. The chemotactic receptor sphingosine-1-phosphate receptor 1 (S1P1; encoded by S1PR1) has a crucial role in regulating thymocyte export.
T cell progenitors enter the thymus close to the cortico–medullary junction which is highly vascularized and the ligand, sphingosine-1-phosphate (S1P), for S1P receptor is produced by neural crest-derived pericytes in the cortico–medullary junction. This is neccessay for the migration of mature single positive thymocytes towards the vascularised cortico–medullary junction and then out of the thymus.