Dendritic cells acquire tolerogenic properties at the site of sterile granulomatous inflammation
Introduction
Subcutaneous implantation of polyvinyl sponges represents a suitable experimental model for studying the pathways of inflammation and subsequent wound healing, triggered by tissue damage. In addition, prolonged persistence of the implanted sponges results in a foreign-body reaction followed by chronic granulomatous inflammation [1], [2].
The sequence of events after the tissue injury is initially characterized by activation of coagulation cascade and complement. Byproducts of these processes drive the development of chemotactic factors that recruit neutrophils, than monocytes and lastly T cells [3]. The majority of monocytes transform into macrophages, but about 25% of these cells differentiate into dendritic cells (DC)1[4]. As it is well known, DC are crucial antigen-presenting cells, promoting both immunity and tolerance [5], [6]. DC in peripheral tissue, such as Langerhans cells in epidermis and dermal (interstitial) DC, originate from their blood precursors or from monocytes [7]. They are functionally immature with limited capacity to activate naive T cells, but with high potential to capture and process antigens. Foreign antigens and inflammatory stimuli increase the recruitment of DC at the sites of inflammation and promote their migration towards regional lymph nodes, where final maturation of DC occurs [8].
Some experimental evidence suggests that DC at the inflammatory site recruit other inflammatory cells, modulate angiogenesis, and promote or suppress local T cell effector functions [9]. These mechanisms are of crucial importance for the regulation of inflammation and wound repair. In addition, DC can be involved in the pathogenesis of numerous chronic inflammatory diseases [10]. However, we are still at the beginning of understanding how DC perform these different functions.
In this study, we used a model of subcutaneous implantation of polyvinyl sponges in rats to study the phenotypic and functional characteristics of DC accumulated into the sponge exudate. Such experiments have not been performed so far. We found that, with the progression of granulomatous inflammation, DC acquire tolerogenic capacity. The relationship of this phenomenon with different DC subsets and cytokine production is discussed.
Section snippets
Animals
AO and DA rats, both sexes, 8–10 weeks old, bred at the Farm for Experimental Animals, Military Medical Academy, Belgrade, were used. AO rats were used in all experiments for the preparation of inflammatory DC, whereas lymph node lymphocytes or T cells of DA rats were used in allogeneic proliferation assays.
Antibodies
The following mouse anti-rat monoclonal antibodies (mAbs) (purified ascites) were used: OX-6 (anti-MHC class II—unconjugated and biotin conjugated), R73 (reactive with αβ-TCR), W3/25
Dynamics of change in the number of DC during inflammation
Inflammatory cells were isolated from implanted sponges at different time points. Cytospins were prepared and stained with OX-6 mAb reactive with rat MHC class II molecule. As presented in Fig. 1, both relative and absolute numbers of OX-6+ cells progressively increased in the inflammatory exudate, reaching maximal values at day 10 following implantation of the sponges. After that, their numbers decreased.
Most OX-6+ cells displayed a morphology characteristic for DC, and up to 20% of them
Discussion
In this work, we studied the dynamics of changes in number, phenotype and functions of inflammatory DC, using a model of subcutaneous implantation of polyvinyl sponges in rats. This model is suitable for studying the processes of acute inflammation and wound healing (early phase) and chronic granulomatous inflammation [1], [15]. To our knowledge, this is the first paper examining DC using such a model of the foreign body response.
We have shown that the number of DC isolated from the sponge
Acknowledgments
We thank Dr. H. Yagita (Jutendo University, Tokyo, Japan), Dr. C. Dijkstra (Free University, Amsterdam, The Netherlands) and Dr. Dammers (University of Groningen, The Netherlands) for generous gifts of 3H5, 2F4; 1B6c; His 24 and His 48 mAbs, respectively.
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