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P045. Macrophage subtypes disrupt the epithelium via deregulated tight junctions and induction of apoptosis

D. Lissner, M. Schumann, C. May, L.-I. Kredel, A. Batra, A. Kühl, J.-D. Schulzke, B. Siegmund, Charite, Hepatology and Gastroenterology Campus Benjamin Franklin, Berlin, Germany

Background

We have shown that pro-inflammatory macrophage subtypes, as found in the lamina propria of patients with Crohn's disease (CD), are capable of disrupting the epithelial barrier. The exact mechanism has not been described yet.

Methods

Unpolarized macrophages (M0) were isolated from human peripheral blood and subsequently polarized into M1- and M2-macrophages. The effect of these cells types on epithelial resistance and thus integrity was analysed after co-culture with different epithelial cell lines (Caco-2, T-84, HT-29/B6). Tight junction proteins (claudin-1 and -2, JAM-1, ZO-1, E-cadherin) and caspase-3 and -8 were analysed by immunostaining and western blot.

Results

Compared to regulatory M2-macrophages, pro-inflammatory M0- and M1 macrophages lead to a massive decrease in epithelial resistance. Mainly, this is due to deregulation of tight junction proteins: The pore-forming protein claudin-2 is significantly up-regulated in M0- and M1-exposed epithelial cells, whereas E-cadherin tends to be decreased in these conditions and increased in M2-exposed cells. Additionally, increased caspase-3 in M0-treated epithelial cells reveals induction of apoptosis as a further mechanism. Here, elevated amounts of active caspase-8 suggest death receptor mediated apoptosis, rather than via mitochondrial regulation.

Conclusion

The disrupting effect of pro-inflammatory macrophages, as found in the lamina propria of patients with CD, on the epithelial barrier is due to deregulated tight junction proteins and induction of death receptor mediated apoptosis.