Analysis of the human thymic perivascular space during aging

The perivascular space (PVS) of human thymus increases in volume during agi ng as thymopoiesis declines. Understanding the composition of the PVS is th erefore vital to understanding mechanisms of thymic atrophy. We have analyz ed 87 normal and 31 myasthenia gravis (MG) thymus tissues from patients ran ging in age from newborn to 78 years, using immunohistologic and molecular assays. We confirmed that although thymic epithelial space (TES) volume dec reases progressively with age, thymopoiesis with active T-cell receptor gen e rearrangement continued normally within the TES into late life. Hematopoi etic cells present in the adult PVS include T cells, B cells, and monocytes . Eosinophils are prominent in PVS of infants 2 years of age or younger. In the normal adult and the MG thymus, the PVS includes mature single-positiv e (CD1a(-) and CD4(+) or CD8(+))T lymphocytes that express CD45RO, and cont ains clusters of T cells expressing the TIA-1 cytotoxic granule antigen, su ggesting a peripheral origin. PBMCs bind in vitro to MECA-79(+) high endoth elial venules present in the PVS, suggesting a mechanism for the recruitmen t of peripheral cells to thymic PVS. Therefore, in both normal subjects and MG patients, thymic PVS may be a compartment of the peripheral immune syst em that is not directly involved in thymopoiesis.