Reactivity of monocyte-derived macrophages from patients with Crohn's disease
Date
2016
Authors
Vennonen, Ingrid
O'Brien, Claire
Pavli, Paul
Bhat, Purnima
Journal Title
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Volume Title
Publisher
Wiley
Abstract
Introduction: While usually seen as an autoimmune disease, the role of
bacteria and pathogen-sensing by antigen presenting cells in the intestinal
mucosa in Crohn's disease (CD) is becoming more apparent. The loss of integrity
of the intestinal monolayer may allow bacterial penetration and trigger
inflammation via interaction with tissue macrophages. Macrophages in
the gut are solely derived from monocyte precursors in peripheral blood.
They become resident (Type 2) macrophages upon entry into the mucosal
environment. However, in CD, monocyte-derived macrophages (MDM)
display Type 1 characteristics of pro-inflammatory cytokine production
and activation. Here, we investigate macrophage interaction with
enterocytes in the presence of pro-inflammatory signals in the gut.
Methods: An “inverted” polarized monolayer of Caco-2 (human
enterocyte) cells was established on membranes (Fig. 1). Monocytes were
isolated from peripheral blood of patients with CD, ulcerative colitis (UC)
or healthy controls (HC) and co-cultured with Caco-2 cells on the
basolateral side of the membrane. We examined the effect of the monocytes
on Caco-2 polarity, monocyte reactivity to enterocytes and their reactivity
to IFN-γ, TNF-α, and LPS from enterotoxigenic E. coli.
Results: Monocytes grown in conditioned media from Caco-2 cells showed
morphologic changes of differentiation, including giant cell formation,
without the need for direct cell-to-cell contact (Fig. 2). Monocytes from
CD patients, but not HC or UC, reduced the TER of monolayers, an indication
of monolayer integrity (Fig. 3A). Examining the membranes by IF
suggested that monocytes were found at the edges of the disrupted monolayer
(Fig. 3B). Macrophages from patients with CD showed a trend to
more IFN-γ expression than macrophages from UC and HC. Intracellular
cytokine staining of monocytes co-cultured with epithelial cells (polarized
and non-polarized) showed no significant differences between markers of
activation such as surface expression of CD69, or intracellular IFN-γ, or
TNF-α. Macrophages from CD patients co-cultured with polarized Caco-
2 cells produced IL10, an anti-inflammatory cytokine, with little pro-inflammatory
IL6 or IL8 produced in response to LPS and TNF-α (Fig. 4).
Conclusion: Monocyte-derived macrophages from peripheral blood interact
with enterocytes in a context-specific manner. Where there is a lack
of polarity of the epithelial layer, it appears that the macrophages may
attempt to support development of monolayer integrity. In the presence
of pro-inflammatory signal therefore, they react in response to both their
preset parameters and the signals they encounter in the gut. In patients with
CD, there is evidence here that some degree of pre-programming influences
their behaviour in this simple model.
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Journal of Gastroenterology and Hepatology
Type
Conference paper
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2099-12-31