Adiratna Mat Ripen, Takeshi Nitta, Shigeo Murata, Keiji Tanaka and Yousuke Takahama (2011). Ontogeny of thymic cortical epithelial cells expressing the thymoproteasome subunit B5t. European Journal of Immunology 41(5): 1278-1287
Proteasomes are responsible for generating peptides presented by class I MHC molecules of the immune system. ?5t, a recently identified proteasome component, is specifically expressed in thymic cortical epithelial cells (cTECs) and plays a pivotal role in generating an immunocompetent repertoire of class I MHC-restricted CD8(+) T cells. Here, we report that ?5t is detectable in the thymus as early as E12.5 mouse embryos. We also found that ?5t expression in cTECs was detectable in mice deficient for RelB or Rag2, indicating that ?5t in cTECs is expressed in the absence of thymic medulla formation or thymocyte development beyond the CD4(-) CD8(-) stage. ?5t expression in the embryonic thymus was not detectable in Foxn1-deficient nude mice, although its expression was not reduced in mice deficient for both CCR7 and CCR9, in which fetal thymus colonization by leukocytes is defective. These results indicate that ?5t expression in cTECs is dependent on Foxn1 but independent of thymocyte crosstalk or thymic medulla formation.