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* = Presenting author

P027 Characterisation of human intestinal dendritic cells and macrophages through the lower gastrointestinal tract.

D. Bernardo*, A. C. Marín, P. M. Linares, M. Jiménez, M. Chaparro, J. P. Gisbert

Hospital Universitario de La Princesa, IIS-IP and CIBERehd, Gastroenterology Unit, Madrid, Spain

Background

Dendritic cells (DC), the most potent antigen presenting cells, are unique on their ability to generate primary (tolerogenic/pro-inflammatory) immune responses. In the gastrointestinal (GI)-tract, DC maintain a balance between tolerance towards nutrients/commensals and immunity against pathogens. Macrophages (MΦ) also maintain GI-homeostasis cooperating with DC to generate regulatory T-cells with suppressor functions. However, it is unknown if intestinal DC and MΦ properties vary through the lower GI tract, which may have relevance in patients with inflammatory bowel disease (IBD) or colorectal cancer with different affected tissues. Here, we aim to characterise DC and MΦ subset composition in the distal colon, proximal colon, and terminal ileum from healthy controls.

Methods

Paired biopsy samples were obtained from the distal colon, proximal colon, and terminal ileum from healthy controls with no known autoimmune disease or malignancies. DC and MΦ were characterised by flow cytometry following quick collagenase digestion.

Results

Human intestinal DC and MΦ were identified within single total viable leukocytes as HLA-DR+CD11c+ and subsequently divided into CD14-CD64- DC or CD14+CD64+ MΦ. DC were further divided into subsets based on the expression of CD103 and SIRPα. CD103-SIRPα+ DC were the main intestinal DC subset which, together with CD103+SIRPα+ DC, were CD1c+ILT3+CD86-. CCR2 was expressed by all CD103-SIRPα+ intestinal DC with its expression being variable on CD103+SIRPα+ DC, where it displayed a negative correlation with CD103 expression. CD103+SIRPα- DC constituted a minor subset of CD141+ILT3-CD86+CCR2- DC. MΦ were divided into ‘high’ and ‘dim’ subsets based on the intensity of CD14 and CD64. The ‘dim’ subset (CD14+CD64+) were CCR2+CD11cloHLA-DRloSIRPα+, whereas the ‘high’ subset (CD14++CD64++) were CCR2-CD11chiHLA-DRhiSIRPα+/-. Macrophage subset could indeed represent newly arrived monocytes (the ‘dim’ subset) that would differentiate into fully mature macrophages (the ‘high’ subset) once they have entered the tissue. Total DC numbers were higher in the proximal colon, where there were lower numbers of total CD103+DC rendering such compartment with a specific reduction of CD103+SIRPα+ DC. On the contrary, MΦ numbers were lower in the terminal ileum, where the ‘high’ subset was absent.

Conclusion

The human GI tract carries different DC and MΦ subsets that change their relative proportions through its length. Immune regional differences should therefore be considered when studying patients with GI-diseases. Current studies are identifying the specific DC and MΦ subsets that are altered in IBD patients with different affected tissues.