Constitutive expression of IDO by dendritic cells of mesenteric lymph nodes: functional involvement of the CTLA-4/B7 and CCL22/CCR4 interactions.
Dendritic cells (DCs) express the immunoregulatory enzyme IDO in response to certain inflammatory stimuli, but it is unclear whether DCs express this enzyme under steady-state conditions in vivo. In this study, we report that the DCs in mesenteric lymph nodes (MLNs) constitutively express functional IDO, which metabolizes tryptophan to kynurenine. In line with a previous report that regulatory T cells (Tregs) can induce IDO in DCs via the CTLA-4/B7 interaction, a substantial proportion of the MLN DCs were located in juxtaposition to Tregs, whereas this tendency was not observed for splenic DCs, which do not express IDO constitutively. When CTLA-4 was selectively deleted in Tregs, the frequency of IDO-expressing DCs in MLNs decreased significantly, confirming CTLA-4's role in IDO expression by MLN DCs. We also found that the MLN DCs produced CCL22, which can attract Tregs via CCR4, and that the phagocytosis of autologous apoptotic cells induced CCL22 expression in CCL22 mRNA-negative DCs. Mice genetically deficient in the receptor for CCL22, CCR4, showed markedly reduced IDO expression in MLN-DCs, supporting the involvement of the CCL22/CCR4 axis in IDO induction. Together with our previous observation that MLN DCs contain much intracytoplasmic cellular debris in vivo, these results indicate that reciprocal interactions between the DCs and Tregs via both B7/CTLA-4 and CCL22/CCR4 lead to IDO induction in MLN DCs, which may be initiated and/or augmented by the phagocytosis of autologous apoptotic cells by intestinal DCs. Such a mechanism may help induce the specific milieu in MLNs that is required for the induction of oral tolerance.
Laboratory of Immunodynamics, Department of Microbiology and Immunology, Osaka University Graduate School of Medicine, Suita, Japan.
Toshiharu
T
Onodera
Myoung Ho
MH
Jang
Zijin
Z
Guo
Mikako
M
Yamasaki
Takako
T
Hirata
Zhongbin
Z
Bai
Noriko M
NM
Tsuji
Daisuke
D
Nagakubo
Osamu
O
Yoshie
Shimon
S
Sakaguchi
Osamu
O
Takikawa
Masayuki
M
Miyasaka
D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018122:B7-1 Antigen / Q000378:metabolism / Q000502:physiology*; D060908:CTLA-4 Antigen; D054422:Chemokine CCL22 / Q000378:metabolism / Q000502:physiology*; D003713:Dendritic Cells / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D005260:Female; D007108:Immune Tolerance / Q000235:genetics; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D007970:Leukopenia / Q000235:genetics / Q000276:immunology; D008198:Lymph Nodes / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D008643:Mesentery; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D054398:Receptors, CCR4 / Q000378:metabolism / Q000502:physiology*
D015703:Antigens, CD; D018122:B7-1 Antigen; D060908:CTLA-4 Antigen; C515483:Ccl22 protein, mouse; C515355:Ccr4 protein, mouse; D054422:Chemokine CCL22; C556707:Ctla4 protein, mouse; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D054398:Receptors, CCR4