The aim of this study was to investigate the

cellular and molecular expression of tartrate resistant acid phosphatase (TRAP) as a marker of activated macrophages in macrophage dependent dextran sulphate sodium (DSS)-induced colitis in rats. In normal colon, TRAP+/CX3CR1+ macrophages were located in the upper part of the lamina propria. In the early stage (day 13) of acute colitis prior to

histopathological changes, induction of the cytokines

TNF, IL-12 and IFNgamma occurred concomitant with

increased mRNA and enzyme activity of TRAP along with

a slight increase of TRAP immunolabelling in macrophages of the upper lamina propria, suggesting induction of TRAP in resident macrophages. Among these cytokines,TNFalpha up-regulated TRAP expression in the RAW 264.7 monocyte/macrophage cell line. In a later phase (day 7) with fulminant colitis, a massive infiltration of macrophages including recruited TRAP+/CCR2+ cells was observed also in the lower part of the lamina propria as well as in the submuscular layer. Additionally, diVerentiated cellular

expression of pro- and mature TRAP also suggest that

mucosal macrophages in the lower part of lamina propria

bordering the sub-mucosa provide a source of replenishment of macrophages situated in the upper lamina propria.

In conclusion, induction of TRAP provides an early sign of macrophage responsiveness in DSS induced colitis