title: Expression of 4-1BB and 4-1BBL in thymocytes during thymus regeneration.
abstract: 4-1BB, a member of the tumor necrosis factor receptor (TNFR) superfamily, is a major costimulatory receptor that is rapidly expressed on the surface of CD4(+) and CD8(+) T cells after antigen- or mitogen-induced activation. The interaction of 4-1BB with 4-1BBL regulates immunity and promotes the survival and expansion of activated T cells. In this study, the expression of 4-1BB and 4-1BBL was examined during regeneration of the murine thymus following acute cyclophosphamide- induced involution. Four-color flow cytometry showed that 4-1BB and 4-1BBL were present in the normal thymus and were preferentially expressed in the regenerating thymus, mainly in CD4(+)CD8(+) double-positive (DP) thymocytes. Furthermore, the CD4(lo)CD8(lo), CD4(+)CD8(lo) and CD4(lo)CD8(+) thymocyte subsets, representing stages of thymocyte differentiation intermediate between DP and single-positive (SP) thymocytes, also expressed 4-1BB and 4-1BBL during thymus regeneration but to a lesser degree. Interestingly, the 4-1BB and 4-1BBL positive cells among the CD4(+)CD8(+) DP thymocytes present during thymus regeneration were TCR(hi) and CD69(+) unlike the corresponding controls. Moreover, the 4-1BB and 4-1BBL positive cells among the intermediate subsets present during thymus regeneration also exhibited TCR(hi/int+) and CD69(+/int) phenotypes, indicating that 4-1BB and 4-1BBL are predominantly expressed by the positively selected population of the CD4(+)CD8(+) DP and the intermediate thymocytes during thymus regeneration. RT-PCR and Western blot analyses confirmed the presence and elevated levels of 4-1BB and 4-1BBL mRNA and protein in thymocytes during thymus regeneration. We also found that the interaction of 4-1BB with 4-1BBL promoted thymocyte adhesion to thymic epithelial cells. Our results suggest that 4-1BB and 4-1BBL participate in T lymphopoiesis associated with positive selection during recovery from acute thymic involution.
authors.affiliation: Department of Pediatrics, Pusan National University School of Medicine, Yangsan 626-870, Korea.
authors.forename: Young-Mi
authors.initials: YM
authors.lastname: Kim
authors.forename: Hye Kyung
authors.initials: HK
authors.lastname: Kim
authors.forename: Hyo Jin
authors.initials: HJ
authors.lastname: Kim
authors.forename: Hee-Woo
authors.initials: HW
authors.lastname: Lee
authors.forename: Seong-A
authors.initials: SA
authors.lastname: Ju
authors.forename: Beom K
authors.initials: BK
authors.lastname: Choi
authors.forename: Byoung S
authors.initials: BS
authors.lastname: Kwon
authors.forename: Bong-Seon
authors.initials: BS
authors.lastname: Kim
authors.forename: Jae-Bong
authors.initials: JB
authors.lastname: Kim
authors.forename: Young-Tak
authors.initials: YT
authors.lastname: Lim
authors.forename: Sik
authors.initials: S
authors.lastname: Yoon
mesh_terms: D053330:4-1BB Ligand / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000378:metabolism; D002448:Cell Adhesion; D002454:Cell Differentiation; D002460:Cell Line; D002478:Cells, Cultured; D003520:Cyclophosphamide / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology; D005786:Gene Expression Regulation; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D012333:RNA, Messenger / Q000235:genetics; D012038:Regeneration; D013601:T-Lymphocytes / Q000166:cytology* / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D053261:Tumor Necrosis Factor Receptor Superfamily, Member 9 / Q000235:genetics / Q000378:metabolism*
chemical_list: D053330:4-1BB Ligand; D007166:Immunosuppressive Agents; D012333:RNA, Messenger; D053261:Tumor Necrosis Factor Receptor Superfamily, Member 9; D003520:Cyclophosphamide