Implantation of any material into the body initiates a cascade of signaling events often producing encapsulation of the implant by an avascular, collagenous, and highly cellularized matrix. This process -- known as the foreign body response -- persists throughout the lifetime of the implant. The resulting fibrous network of collagen is thought to be produced by fibroblasts acting on cues from resident macrophages. As the primary modulators of the foreign body response, macrophages secrete many different cytokines at the site of injury. The precise intracellular signaling is largely unknown. Understanding the cooperative nature of these cells is important in gaining further knowledge toward the development and possible control of fibrotic encapsulation.

To evaluate the effects that macrophages have on fibroblastic collagen production, a non-contacting cell co-culture system was implemented using both secondary and primary murine-derived cells. As the time course for triggering the formative components of the foreign body response is approximately three weeks, cells were co-cultured for 21 days on tissue culture polystyrene (TCPS) as previously described.^1-4 TCPS may activate macrophages over time and change their cytokine secretion profiles, which may in turn affect the behavior of the fibroblasts. Cell culture media was collected at days 1, 2, 3, 7, 14, and 21 and tested for changes in soluble protein secretion. A cytometric bead array (CBA) assay using flow cytometry was used to determine cytokine profiles over time. Mouse IL-2, IL-3, IL-4, IL-5, IL-6, IL-9, IL-10, IL-12p70, IL-13, MCP-1, TNF, MIP-1á, MIP-1â, GM-CSF, IFNã, and RANTES were evaluated. A collagen assay was employed to determine variations in fibroblast collagen production both isolated and co-cultured with macrophage-lineage cells. All cells were imaged frequently on surfaces in cultures to determine any changes in behavior and morphology.

The co-culture system demonstrated was found to induce increased collagen production by fibroblasts and alter cytokine profiles over time, compared to those from mono-cultured fibroblasts. These profiles will be related to phenotypic behaviors in these cells in the foreign body response.

References:

1.M.L. Godek, G.S. Malkov, E.R. Fisher, D.W. Grainger, “Macrophage serum-based adhesion to surface chemistry is distinct from that exhibited by fibroblasts,” Plasma Proc. Polym., 3, 485-497, (2006).

2.M.L. Godek, J.A. Sampson, N.L. Duchsherer, Q. McElwee, D.W. Grainger, “Rho GTPase protein expression and activation in murine monocyte/macrophages is not modulated by model biomaterial biomaterial culture surfaces,” J. Biomat. Sci. Polym.

3.M.L. Godek, R. Michel, L.M. Chamberlain, D.G. Castner, D.W. Grainger, “Adsorbed serum albumin is permissive to macrophage attachment to polymer surfaces in culture”, J. Biomed. Mat. Res., under revision, (2007).

4.L.M. Chamberlain, M.L. Godek, M. Gonzalez-Juarrero, D.W. Grainger, “Comparison of murine macrophage cell models for in vitro assessment of the foreign body response”, submitted to J. Biomed. Mater. Res., 2007.