title: Tolerance and Cross-Tolerance following Toll-Like Receptor (TLR)-4 and -9 Activation Are Mediated by IRAK-M and Modulated by IL-7 in Murine Splenocytes.
abstract: OBJECTIVE
  Immune suppression during critical illness predisposes to serious infections. We sought to determine the mechanisms regulating tolerance and cross-tolerance to common pro-inflammatory danger signals in a model that recapitulates the intact in vivo immune response.
  
  
  METHODS
  Flt3-expanded splenocytes obtained from wild-type or matching IRAK-M knockout (IRAK-M-/-), C57BL/6, male mice (8-10 weeks old) were treated repeatedly or alternately with either LPS or CpGA DNA, agonists of Toll-like receptor (TLR)-4 and -9, respectively, over successive 24-hour periods. Supernatants were collected following each 24-hour period with cytokine release (ELISA) and splenocyte IRAK-M expression (Western blot) determined. Tolerance and cross-tolerance were assessed in the absence or presence of programmed death receptor (PD)-1 blocking antibody or IL-7 pre-treatment.
  
  
  RESULTS
  Splenocytes notably exhibited both tolerance and cross-tolerance to subsequent treatments with either LPS or CpGA DNA. The character of tolerance and cross-tolerance in this model was distinct following initial LPS or CpGA treatment in that TNFα and IFNγ release (not IL-10) were suppressed following LPS; whereas, initial CpGA treatment suppressed TNFα, IFNγ and IL-10 release in response to subsequent stimulation (LPS or CpGA). Tolerance and cross-tolerance were unrelated to IL-10 release or PD-1 but were attenuated in IRAK-M-/- splenocytes. IL-7 significantly suppressed IRAK-M expression and restored TNFα and IFNγ production without influencing IL-10 release.
  
  
  CONCLUSIONS
  In summary, acute immune tolerance and cross-tolerance in response to LPS or CpGA were distinct in that LPS selectively suppressed pro-inflammatory cytokine responses; whereas, CpGA suppressed both pro- and anti-inflammatory responses. The induction of tolerance and cross-tolerance in response to common danger signals was mechanistically unrelated to IL-10 or PD-1 but was directly influenced by IRAK-M expression. IL-7 reduced IRAK-M expression and attenuated immune tolerance induced by either LPS or CpGA, and thus may be useful for reversal of immune tolerance in the setting of critical illness.
authors.affiliation: Dorothy M. Davis Heart and Lung Research Institute, Division of Pulmonary Allergy, Critical Care, and Sleep Medicine, Wexner Medical Center, Columbus, OH, United States of America.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Julian
authors.affiliation: College of Veterinary Medicine, Department of Veterinary Biosciences, The Ohio State University, Columbus, OH, United States of America.
authors.forename: Heather R
authors.initials: HR
authors.lastname: Strange
authors.affiliation: Dorothy M. Davis Heart and Lung Research Institute, Division of Pulmonary Allergy, Critical Care, and Sleep Medicine, Wexner Medical Center, Columbus, OH, United States of America.
authors.forename: Megan N
authors.initials: MN
authors.lastname: Ballinger
authors.affiliation: Departments of Anesthesiology, Medicine and Surgery, Washington University School of Medicine, St. Louis, MO, United States of America.
authors.forename: Richard S
authors.initials: RS
authors.lastname: Hotchkiss
authors.affiliation: College of Veterinary Medicine, Department of Veterinary Biosciences, The Ohio State University, Columbus, OH, United States of America.
authors.forename: Tracey L
authors.initials: TL
authors.lastname: Papenfuss
authors.affiliation: Dorothy M. Davis Heart and Lung Research Institute, Division of Pulmonary Allergy, Critical Care, and Sleep Medicine, Wexner Medical Center, Columbus, OH, United States of America.
authors.forename: Elliott D
authors.initials: ED
authors.lastname: Crouser
mesh_terms: D000818:Animals; D007108:Immune Tolerance; D007371:Interferon-gamma / Q000235:genetics / Q000276:immunology; D053592:Interleukin-1 Receptor-Associated Kinases / Q000235:genetics / Q000276:immunology*; D016753:Interleukin-10 / Q000235:genetics / Q000276:immunology; D015851:Interleukin-7 / Q000235:genetics / Q000276:immunology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009838:Oligodeoxyribonucleotides / Q000494:pharmacology; D013154:Spleen / Q000166:cytology / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology*; D051217:Toll-Like Receptor 9 / Q000235:genetics / Q000276:immunology*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000276:immunology
chemical_list: C408982:CPG-oligonucleotide; C556062:IL10 protein, mouse; D015851:Interleukin-7; D008070:Lipopolysaccharides; D009838:Oligodeoxyribonucleotides; C493487:Tlr4 protein, mouse; C495370:Tlr9 protein, mouse; D051197:Toll-Like Receptor 4; D051217:Toll-Like Receptor 9; D014409:Tumor Necrosis Factor-alpha; C576410:interleukin-7, mouse; D016753:Interleukin-10; D007371:Interferon-gamma; D053592:Interleukin-1 Receptor-Associated Kinases; C507772:Irak3 protein, mouse