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P103. Adding fuel to the fire – neutrophils as antigen presenting cells in Crohn's disease

R. Somasundaram1, C.J. van der Woude1, M. Peppelenbosch1, G. Fuhler1, 1Erasmus mc, Gastroenterology and Hepatology, Rotterdam, Netherlands

Background

Neutrophils (PMN) are the first line of defence against bacterial infection. However, they may also act as antigen-presenting cells (APCs), as is observed in inflammatory diseases like rheumatoid arthritis and bacterial infections. During inflammation, PMN are exposed to proinflammatory cytokines which not only influence PMN survival, but upon prolonged exposure can also lead to their dedifferentiation towards an APC-like phenotype. PMN influx at the site of inflammation in Crohn's disease (CD) has been described. However, the functional consequences of their presence remain controversial. Here, we show that PMN in mucosa from CD patients acquire APC characteristics.

Methods

Freshly isolated peripheral blood PMN from healthy volunteers (HC) and CD patients were cultured for 3 days in the presence of GMCSF 50U/ml, IFNγ 100U/ml, IL4 3 ng/ml. Expression of CD80, CD86, MHCII on CD66b+ PMN were measured by flowcytometry in peripheral blood and single cell suspensions from biopsies. PMN expression of MHCII at the site of inflammation was determined by double labelling of biopsies.

Results

PMN present in the peripheral blood from CD patients and HCs did not express the co-receptors for antigen presentation. However, mucosal PMN from fresh CD biopsies did express APC co-receptors, both at site of inflammation and in non-inflamed regions (n = 5, 13±2% of PMN vs 15±6%). In contrast, mucosal PMN from healthy control biopsies did not express CD80, CD86 or MHC II. As a confirmation of the flowcytometric data, biopsies from CD patients and HCs were stained for MHCII in conjunction with the PMN marker CD66b. Double positive cells were found only in active CD colonic and small intestinal biopsies. To investigate whether the propensity to dedifferentiate was intrinsically enhanced in CD PMN, peripheral blood PMN were cultured in the presence of a cytokine cocktail, inducing dedifferentiation and expression of CD80, CD86, MHC II. However, similar percentages of PMN expressed APC markers in CD (9.6±6%, n = 8) and HC (15±10.6%, n = 11) in vitro.

Conclusion

We show for a first time that a subset of PMN in active CD patients expresses APC co-receptors. Induction of redifferentiation of PMN from CD and HC in vitro is not different, indicating that in all likelyhood, the local presence of pro-inflammatory cytokines induces this dedifferentiation of mucosal PMN in CD patients. This may serve to enhance presentation of bacterial antigens to T cells, thereby adding fuel to the already over-activated T cell response in CD.