Detection of muramyl dipeptide-sensing pathway defects in patients with Crohn's disease.
OBJECTIVE
Crohn's disease is strongly associated with double mutations in NOD2/CARD15. Three common mutations (Arg702Trp, Gly908Arg, Leu1007fs) impair innate immune responses to bacterial muramyl dipeptide. Rare NOD2 variants occur, but it is difficult to both identify them and assess their functional effect. We assessed the true frequency of defective muramyl dipeptide sensing in Crohn's disease and developed a rapid diagnostic assay.


METHODS
An ex vivo assay was established and validated based on muramyl dipeptide stimulation of peripheral blood mononuclear cell cytokine production. Muramyl dipeptide-induced enhancement of interleukin (IL)-8 secretion and synergistic increase in lipopolysaccharide-induced IL-1beta secretion were studied. Assay results were compared with NOD2 genotype status (3 common mutations and rare variants) in 91 individuals including a prospective cohort of 49 patients with Crohn's disease.


RESULTS
The assay was highly sensitive and specific for detection of profound defects in muramyl dipeptide sensing caused by double NOD2 mutations (IL-8 P = 0.0002; IL-1beta P = 0.0002). Disease state, active inflammation, or concurrent use of immunosuppressive medication did not influence results. Healthy NOD2 heterozygotes had modest impairment of muramyl dipeptide induced IL-8 secretion (P = 0.003). Only 1 of 7 patients with Crohn's disease with both a common mutation and a rare variant had a profound muramyl dipeptide-sensing defect.


CONCLUSIONS
Profound defects in muramyl dipeptide sensing were found in 10% of patients with Crohn's disease. Defects were caused exclusively by inherited mutations in NOD2. The ex vivo assay has multiple potential applications as a clinical diagnostic tool to distinguish patients with muramyl dipeptide-sensing defects and for research investigation.
van Heel
David A
DA
Institute of Cell and Molecular Science, Barts & The London, Queen Mary's School of Medicine & Dentistry, London, UK. d.vanheel@qmul.ac.uk
Hunt
Karen A
KA
King
Kathy
K
Ghosh
Subrata
S
Gabe
Simon M
SM
Mathew
Christopher G
CG
Forbes
Alastair
A
Playford
Raymond J
RJ
D000119:Acetylmuramyl-Alanyl-Isoglutamine / Q000097:blood / Q000737:chemistry*; D003424:Crohn Disease / Q000097:blood / Q000235:genetics* / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D005838:Genotype; D006579:Heterozygote; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007249:Inflammation; D053583:Interleukin-1beta / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism; D009000:Monocytes / Q000378:metabolism; D009154:Mutation; D012680:Sensitivity and Specificity
D016207:Cytokines; D007166:Immunosuppressive Agents; D053583:Interleukin-1beta; D016209:Interleukin-8; D008070:Lipopolysaccharides; D000119:Acetylmuramyl-Alanyl-Isoglutamine