The foreign body response to biomaterial implants is reduced by co-inhibition of TLR2 and TLR4

The foreign body response (FBR) is a formidable reaction that occurs to any non-biological implantable biomaterial and results in fibrous encapsulation. Non-specific protein adsorption is the first stage of the FBR and is thought to initiate the response by activation of innate immune cells. Here we show that Toll-like receptors (TLRs) 2 and 4 are the primary receptors responsible for recognizing surface adsorbed proteins as damage associated molecular patterns (DAMPs) and they determine the material dependent FBR. An in vitro model using multiple biomaterials identified that macrophages, not neutrophils, respond to surface-adsorbed plasma via TLR2 and/or TLR4 and that deletion of both was required to inhibit activation across all materials. In the more complex in vivo environment, simultaneous deletion of TLR2 and TLR4 nearly abrogated the FBR to multiple biomaterials and eliminated the material dependencies in a subcutaneous implant mouse model. Deletion of either TLR2 or TLR4 showed either no effect or a partial reduction, depending on the material, demonstrating that TLRs determine the material-dependent FBR in vivo. Collectively, we identified TLR2 and TLR4 as necessary receptors for the FBR and implicate macrophage recognition of DAMPs of surface-adsorbed proteins, which vary depending on the material, as the main driver initiating the FBR. Our findings establish TLR2 and TLR4 as therapeutic targets to evade the FBR across a range of implantable materials. STATEMENT OF SIGNIFICANCE: Synthetic biomaterials when implanted elicit a foreign body response (FBR) leading to fibrous encapsulation. The mechanisms however are not fully understood. When a biomaterial is implanted, proteins non-specifically adsorb to the material. These proteins may act as damaged associated molecular patterns (DAMPs) to induce inflammation. Toll like receptor (TLR) 2 and 4 are known receptors that recognize DAMPs. This work investigated several different biomaterials and found that TLR2 and TLR4 mediate the FBR in a material-dependent manner. Deleting both TLR2 and TLR4 was necessary to inhibit significantly fibrous capsule formation across all materials tested. Our findings provide direct evidence that DAMPs are the main driver of the FBR and establish TLR2/4 as potential therapeutic targets to evade the FBR.