RESUMO
Muramyl dipeptide (MDP), a product of bacterial cell-wall peptidoglycan, activates innate immune cells by stimulating nucleotide-binding oligomerization domain containing 2 (NOD2) -dependent activation of the transcription factor NFkappaB and transcription of proinflammatory genes. A20 is a ubiquitin-modifying enzyme that restricts tumor necrosis factor (TNF) receptor and Toll-like receptor (TLR) -induced signals. We now show that MDP induces ubiquitylation of receptor- interacting protein 2 (RIP2) in primary macrophages. A20-deficient cells exhibit dramatically amplified responses to MDP, including increased RIP2 ubiquitylation, prolonged NFkappaB signaling, and increased production of proinflammatory cytokines. In addition, in vivo responses to MDP are exaggerated in A20-deficient mice and in chimeric mice bearing A20-deficient hematopoietic cells. These exaggerated responses occur independently of the TLR adaptors MyD88 and TRIF as well as TNF signals. These findings indicate that A20 directly restricts NOD2 induced signals in vitro and in vivo, and provide new insights into how these signals are physiologically restricted.
Assuntos
Cisteína Endopeptidases/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteína Adaptadora de Sinalização NOD2/metabolismo , Transdução de Sinais/fisiologia , Ubiquitinação/fisiologia , Acetilmuramil-Alanil-Isoglutamina/farmacologia , Animais , Macrófagos/metabolismo , Camundongos , Camundongos Mutantes , NF-kappa B/metabolismo , Proteína Serina-Treonina Quinase 2 de Interação com Receptor , Proteína Serina-Treonina Quinases de Interação com Receptores/metabolismo , Proteína 3 Induzida por Fator de Necrose Tumoral alfa , Ubiquitina/metabolismoRESUMO
Toll-like receptors (TLRs) on host cells are chronically engaged by microbial ligands during homeostatic conditions. These signals do not cause inflammatory immune responses in unperturbed mice, even though they drive innate and adaptive immune responses when combating microbial infections. A20 is a ubiquitin-modifying enzyme that restricts exogenous TLR-induced signals. We show that MyD88-dependent TLR signals drive the spontaneous T cell and myeloid cell activation, cachexia, and premature lethality seen in A20-deficient mice. We have used broad spectrum antibiotics to demonstrate that these constitutive TLR signals are driven by commensal intestinal flora. A20 restricts TLR signals by restricting ubiquitylation of the E3 ligase tumor necrosis factor receptor-associated factor 6. These results reveal both the severe proinflammatory pathophysiology that can arise from homeostatic TLR signals as well as the critical role of A20 in restricting these signals in vivo. In addition, A20 restricts MyD88-independent TLR signals by inhibiting Toll/interleukin 1 receptor domain-containing adaptor inducing interferon (IFN) beta-dependent nuclear factor kappaB signals but not IFN response factor 3 signaling. These findings provide novel insights into how physiological TLR signals are regulated.
Assuntos
Cisteína Endopeptidases/imunologia , Inflamação/imunologia , Peptídeos e Proteínas de Sinalização Intracelular/imunologia , Fator 88 de Diferenciação Mieloide/imunologia , Receptores Toll-Like/imunologia , Proteínas Adaptadoras de Transporte Vesicular/imunologia , Animais , Cisteína Endopeptidases/deficiência , Cisteína Endopeptidases/genética , Células-Tronco Hematopoéticas/imunologia , Homeostase , Peptídeos e Proteínas de Sinalização Intracelular/deficiência , Peptídeos e Proteínas de Sinalização Intracelular/genética , Lipopolissacarídeos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Peritonite/induzido quimicamente , Peritonite/imunologia , Linfócitos T/imunologia , Fator 6 Associado a Receptor de TNF/imunologia , Proteína 3 Induzida por Fator de Necrose Tumoral alfa , UbiquitinaçãoRESUMO
BACKGROUND: The crypt lamina propria of the mouse small intestine has been shown to harbor multiple tiny clusters filled with c-kit- and interleukin 7 receptor (IL-7R)-positive lympho-hemopoietic cells (cryptopatches; CPs). However, it has remained an open question whether similar lymphoid tissue are present in the gastrointesitinal tract in other animals. In the present study, we investigated whether the small intestine of rats harbored lymphoid tissues similar to mouse CPs. METHODS: Immunohistochemical and flow cytometric analyses were carried out using various antibodies, including those to c-kit and IL-7R molecules. RESULTS: Lymphocyte-filled villi (LFVs), populated predominantly with c-kit- and IL-7 receptor (IL-7R)-positive cells and less with T cell receptor (TCR)-alphabeta T cells were found throughout the small intestine of young adult rats. Although LFVs were absent from fetal rat intestine, they were first detected at around 2 weeks after birth. Notably, in most LFVs that settled in the antimesenteric wall of the small intestine in young adult rats, immunoglobulin M-positive B cells were also detectable at the bottom of the LFVs. In aged rats, lymphocytes in some LFVs displayed a different phenotype, comprising a large B-cell area that included a germinal center. Thus, these clusters represent the first description of isolated lymphoid follicles (ILFs) in the rat small intestine. CONCLUSIONS: The present study provides the first evidence for c-kit- and IL-7R-positive lymphocyte clusters in the rat small intestine. Our data also indicating that LFVs and ILFs may constitute novel organized gut-associated lymphoid tissues in lamina propria of the rat small intestine.
Assuntos
Intestino Delgado/anatomia & histologia , Tecido Linfoide/anatomia & histologia , Animais , Ratos , Ratos WistarRESUMO
A20 is a cytoplasmic protein required for the termination of tumor necrosis factor (TNF)-induced signals. We show here that mice doubly deficient in either A20 and TNF or A20 and TNF receptor 1 developed spontaneous inflammation, indicating that A20 is also critical for the regulation of TNF-independent signals in vivo. A20 was required for the termination of Toll-like receptor-induced activity of the transcription factor NF-kappaB and proinflammatory gene expression in macrophages, and this function protected mice from endotoxic shock. A20 accomplished this biochemically by directly removing ubiquitin moieties from the signaling molecule TRAF6. The critical function of this deubiquitinating enzyme in the restriction of TLR signals emphasizes the importance of the regulation of ubiquitin conjugation in innate immune cells.