Toll-like receptor mediated responses to adsorbed damage-associated molecular patterns on biomaterial surfaces
Macrophage , Toll-like receptor , Foreign body reaction , Protein adsorption , Polymeric biomaterials , Damage-associated molecular patterns , Insulin infusion cannulas , Inflammatory response , Immunology
The foreign body reaction is a chronic inflammatory response to an implanted biomaterial that ultimately leads to fibrous encapsulation of the implant. It is widely accepted that the host response to implanted biomaterials is largely dependent on the species and conformations of proteins adsorbed onto the material surface, due to the adsorbate’s role in mediating cellular interactions with the implanted material. While the cellular response to adsorbed serum-derived proteins has been studied extensively, the presence of endogenous, matrix- and cell-derived mediators of inflammation within the adsorbed protein layer and their impact on cell-material interactions is not well understood. Damage-associated molecular patterns (DAMPs) are endogenous ligands released by stressed or damaged tissues to stimulate sterile inflammatory responses via Toll-like receptors (TLRs) and other pattern recognition receptors. The work in this thesis explored the contribution of cellular damage molecules in cell lysate and TLR signalling in macrophage responses to a range of non-resorbable polymers, including insulin infusion cannulas. The in vitro data showed that adsorbed DAMPs on polymeric surfaces, both alone and in the presence of blood proteins, strongly induced NF-B/AP-1 transcription factor activity and pro-inflammatory cytokine secretion in reporter macrophages, compared to serum- and plasma-adsorbed surfaces. Lysate-dependent NF-B/AP-1 activation and cytokine production was strongly attenuated by TLR2 neutralizing antibodies. Work with primary bone marrow-derived macrophages confirmed the similar contribution of TLR2- and MyD88-dependent signalling in pro-inflammatory, anti-inflammatory, and angiogenic cytokine gene expression and production in response to model cannula surfaces with adsorbed DAMPs and plasma. Trends in the results from short term cannula implants in wildtype (WT) and TLR-knockout mice demonstrated that, while WT mice had an increase in inflammation over the 7 days, TLR2-/- and MyD88-/- mice had a decreasing trend. Furthermore, TLR2-/- and MyD88-/- mice had similar inflammatory cell layer thicknesses after 7 days, which were thinner than in WT mice. The results of the work presented here demonstrate that TLR2- and MyD88-dependent signalling are promising targets to modulate the acute inflammatory response, and merit further investigation.