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* = Presenting author

P057 The T-cell compartment of the adipose tissue-differences of Crohn's disease and obesity

L.I. Kredel*1, A.A. Kuehl1, C. Romagnani2, I. Freise1, J. Gröne3, J. Ordemann4, B. Siegmund1

1Charité, Campus Benjamin Franklin, Gastroenterology, Infectiology and Rheumatology, Berlin, Germany, 2Deutsches Rheuma-Forschungszentrum, Angeborene Immunität, Berlin, Germany, 3Charité Universitätsmedizin Berlin, CBF, General, Vascular and Thoracic Surgery, Berlin, Germany, 4Charité, Campus Mitte, Center for Obesity and Metabolic Surgery, Berlin, Germany

Background

Creeping fat (CF), a hyperplasia of the mesenteric fat adjacent to the inflamed segments of the intestine, is pathognomonic for Crohn's disease (CD). While fat accumulation in CD is locally restricted, it is generalized in obesity (OB). Today OB is categorized not only as a form of body constitution but rather as a chronic inflammatory state. Since a destroyed mucosal barrier is pathophysiolocically highly relevant in CD, it seems interesting that OB induces an impaired barrier function and intestinal inflammation in rodents. In both diseases distinct alterations within the cellular, humoral, and stromal compartments have been described. While adipose tissue inflammation is believed to be a main player in the systemic consequences of OB, the impact of adipose tissue immune cells in CD is less defined. Whether the immunological processes within the fat contribute to the intestinal inflammation or if the hyperplastic fat might exert a protective function for the organism, is still controversially discussed.

We aim to perform a comparative characterization of the immune-cell department of CD and OB patients in order to reveal the contribution of adipose tissue immune cells for both inflammatory conditions.

Methods

Mesenteric/visceral fat (5-10g) was collected from patients with CD, undergoing surgery because of disease-related complications, and visceral fat from obese patients, undergoing bariatric surgery. Small fractions were fixed in formalin and paraffin. Immune histological staining was performed. Immune cells were isolated from the tissue and lymphocytes were analyzed by flow cytometry.

Results

The morphological pattern of immune cell infiltration differs in CD and OB. While in OB, infiltrating cells are arranged in small groups, widespread inside the tissue; In CD cells accumulate close to the mucosal border. With over 20%, lymphocytes represent a major group of non-adipocytes within the CF. In OB their percentage is significantly lower. In both conditions CD4+ T-cells are higher in number compared to CD8+ T-cells. Interestingly, their activation status differs significantly. While in OB memory-T-cells represent the majority, there is a strong infiltration of naive T-cells into the CF in CD.

Conclusion

Inflammatory processes within the intra-abdominal adipose-tissue impact (intestinal) inflammation in CD and OB. Adipose tissue immune cells contribute to the systemic consequences of OB. The inflammatory processes in intra-abdominal adipose tissue in OB and CD differ significantly; hence adipose tissue inflammation in CD might impact inflammatory processes in other, probably even protective, ways.