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* = Presenting author

P005 Characterization of human colonic and ileal dendritic cells in health and Crohn's disease

I. Moret-Tatay*1, 2, 3, Y.H. Siaw1, 4, R. Man5, H.O. Al-Hassi1, R. Vora1, 4, D. Reddi1, A.L. Hart4, B. Beltrán3, 6, P. Nos3, 6, S.C. Knight**1, D. Bernardo**1

1Imperial College London, Northwick Park and St. Mark's Campus, Antigen Presentation Research Group, Harrow, HA1 3UJ, United Kingdom, 2IIS Hospital La Fe, Gastroenterology, Valencia, Spain, 3Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas, CIBERehd, , Spain, 4St. Mark's Hospital, North West London Hospitals NHS Trust, Digestive Medicine, Harrow, HA1 3UJ, United Kingdom, 5St. Mark's Hospital, North West London Hospitals NHS Trust, Wolfson Unit for Endoscopy, Harrow, HA1 3UJ, United Kingdom, 6Hospital Universitari i Politècnic La Fe, Digestive Medicine, Valencia, Spain

** - both authors have contributed equally to the paper

Background

Human intestinal dendritic cells (DC) maintain a balance between tolerance to nutrients/commensals and immunogenicity against pathogens. Changes in intestinal DC properties are found in inflammatory bowel diseases including Crohn's disease (CD). Most studies, however, do not consider DC compartmentalization through the human gut. Here we studied whether DC subsets and phenotype change through the human gut in healthy controls (HC) and CD patients.

Methods

Paired biopsies from human proximal colon and the terminal ileum (TI) were obtained from HC and CD patients. DC were identified following collagenase digestion where DC phenotype were assessed by flow cytometry. Antigen presenting cells (CD45+HLA-DRhigh) were identified within single viable cells. Discrimination between DC and Mφ was subsequently performed based on lineage marker expression (CD3,CD14,CD16,CD19,CD34) and side scatter properties of the cells identifying DC as CD45+HLA-DR+lineage-complexitylow. DC were further distinguished from Mφ as CD64- with CCR7 up-regulation following overnight culture.

Results

In all samples, intestinal DC were myeloid (mDC, CD11c+) and were further divided into different subsets based on CD103 and SIRPα expression. CD103-SIRPα+ and CD103+SIRPα+ were type 1 immature mDC (CD1c+CD141-ILT3+) while CD103+SIRPα- were type 2 mature mDC (CD1c-CD141+ILT3-). CCR2 was expressed in all CD103-SIRPα+ DC, with expression being variable on CD103+SIRPα+ and absent on CD103+SIRPα- DC.

In HC, total DC numbers were higher in the proximal colon compared with the TI with no differences in the CD103/SIRPα DC subset composition between compartments. However, the TI from HC carried higher numbers of CCR2+DC and CD11cdimCD1c-DC.

In CD patients compared with healthy controls, DC numbers were higher in both the colon and the TI and displayed a specific reduction of CD103+SIRPα+ DC in both tissues. CCR2 expression on ileal and colonic DC did not differ between HC and CD. In CD, however, the proportion of ileal CD11cdimCD1c- DC was lower in CD patients than in HC, an effect that was not seen in the proximal colon. Finally, TLR2 and TLR4 expression were higher in both the colon and TI from CD patients, compared with the healthy matched tissue, due to a specific up-regulation of CD11c+CD1c+DC.

Conclusion

DC subsets and phenotype change through the length of the human gastrointestinal tract and display different tissue-specific alteration in CD patients. Tissue compartmentalization is, therefore, likely to affect the Results of studies addressing the immune system of the human gut, both in health and disease.