title: Dendritic cells control CD4+CD25+ Treg cell suppressor function in vitro through juxtacrine delivery of IL-2.
abstract: CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) restrict inflammatory responses to self and nonself. Aberrant Treg activity is pathologic: Insufficient Treg activity is implicated in autoimmunity, allergy, and graft-versus-host-disease; overabundant activity is implicated in chronic infection and cancer. Tregs require IL-2 for their expansion and acquisition/execution of suppressor function; however, because Tregs cannot produce IL-2, they depend on IL-2 from an exogenous source. Until now, that IL-2 source had not been established. We asked whether dendritic cells (DCs) could supply IL-2 to Tregs and, if so, what was required for that delivery. We used flow cytometry, IL-2 ELISPOT, RT-qPCR, and IL-2 promoter-driven reporter assays to measure intracytoplasmic IL-2, secreted protein, IL-2 message and IL-2 promoter activity in bone marrow-derived (BMDC) and splenic DCs. We examined conjugate formation between Tregs, conventional CD4(+) cells, and IL-2-expressing DCs. We measured Treg levels of CD25, Foxp3, and suppressor function after co-culture with IL-2 sufficient and IL-2(-/-) DCs. We generated IL-2-mCherry-expressing DCs and used epifluorescence microscopy and flow cytometry to track IL-2 transfer to Tregs and test requirements for transfer. Between 0.7 to 2.4% of DCs constitutively produced IL-2 and diverted IL-2 secretion to Tregs by preferentially forming conjugates with them. Uptake of DC IL-2 by Tregs required cell-cell contact and CD25. Tregs increased levels of CD25 and Foxp3 from baseline and showed greater suppressor function when co-cultured with IL-2-sufficient DCs, but not when co-cultured with IL-2(-/-) DCs. Exogenous IL-2, added in excess of 500 U/ml to co-cultures with IL-2(-/-) DCs, restored Treg suppressor function. These data support a model of juxtacrine delivery of IL-2 from DCs to Tregs and suggest that a subset of DCs modulates Treg function through controlled, spatial delivery of IL-2. Knowledge of how DCs regulate Tregs should be integrated into the design of interventions intended to alter Treg function.
authors.affiliation: Department of Medicine, Roy J and Lucille A. Carver College of Medicine, The University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Katarina
authors.initials: K
authors.lastname: Kulhankova
authors.forename: Todd
authors.initials: T
authors.lastname: Rouse
authors.forename: Mohamed E
authors.initials: ME
authors.lastname: Nasr
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Field
mesh_terms: D000818:Animals; D015704:CD4 Antigens / Q000378:metabolism*; D002450:Cell Communication; D049109:Cell Proliferation; D003713:Dendritic Cells / Q000166:cytology / Q000276:immunology*; D051858:Forkhead Transcription Factors / Q000378:metabolism; D007376:Interleukin-2 / Q000235:genetics / Q000378:metabolism*; D053645:Interleukin-2 Receptor alpha Subunit / Q000378:metabolism*; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D010641:Phenotype; D050378:T-Lymphocytes, Regulatory / Q000166:cytology / Q000276:immunology*; D014158:Transcription, Genetic
chemical_list: D015704:CD4 Antigens; D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse; D007376:Interleukin-2; D053645:Interleukin-2 Receptor alpha Subunit