title: Exogenous IL-7 increases recent thymic emigrants in peripheral lymphoid tissue without enhanced thymic function.
abstract: Interleukin 7 (IL-7) is critical in maintaining thymic-dependent and thymic-independent pathways of T-cell homeostasis. T-cell receptor (TCR) rearrangement excision circles (TRECs) have been used as markers for recent thymic emigrants (RTEs) in assessing human thymic function. To study the thymic and peripheral effects of IL-7 on RTEs, we measured TREC content and peripheral naive T-cell subsets and turnover in IL-7-treated mice. Short-term administration of IL-7 into thymus-intact mice resulted in increased total TREC numbers, consistent with RTE accumulation. Decreases in TREC frequency were attributable to dilution secondary to increased cell turnover. Significantly, IL-7 administration into thymectomized mice resulted in patterns of decreased TREC frequency and increased total TREC number similar to those in IL-7-treated thymus-intact mice. Distinct patterns of naive cell and RTE distribution among peripheral immune organs and altered expression of CD11a were observed following IL-7 treatment in thymus-intact and thymectomized mice. These results demonstrate (1) that total TREC number and not TREC frequency accurately reflects quantitative changes in RTEs; (2) that short-term IL-7 administration results in preferential accumulations of RTEs among peripheral immune organs, accounting for the increase in TRECs in the total peripheral lymphoid pool; and (3) no evidence for regulation of thymic function by short-term IL-7 administration.
authors.affiliation: Experimental Immunology Branch, Center for Cancer Research, NIH, Bldg 10, Rm 4B14, 10 Center Dr, Bethesda, MD 20892-1360, USA. chuy@mail.nih.gov
authors.forename: Yu-Waye
authors.initials: YW
authors.lastname: Chu
authors.forename: Sarfraz A
authors.initials: SA
authors.lastname: Memon
authors.forename: Susan O
authors.initials: SO
authors.lastname: Sharrow
authors.forename: Frances T
authors.initials: FT
authors.lastname: Hakim
authors.forename: Michael
authors.initials: M
authors.lastname: Eckhaus
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Lucas
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Gress
mesh_terms: D000818:Animals; D040881:CD11a Antigen / Q000032:analysis; D002465:Cell Movement / Q000187:drug effects*; D015329:Gene Rearrangement, T-Lymphocyte; D006706:Homeostasis / Q000276:immunology; D015851:Interleukin-7 / Q000494:pharmacology*; D008198:Lymph Nodes / Q000166:cytology; D008221:Lymphoid Tissue / Q000166:cytology*; D051379:Mice; D008810:Mice, Inbred C57BL; D013154:Spleen / Q000166:cytology; D016176:T-Lymphocyte Subsets; D013934:Thymectomy; D013950:Thymus Gland / Q000166:cytology* / Q000502:physiology
chemical_list: D040881:CD11a Antigen; D015851:Interleukin-7