TOLL like receptor 4 is involved in inflammatory reactions (overgrowth) against alginate capsules

Alginate capsules are currently investigated as bioreactors for delivering therapeutic molecules like insulin and cancer inhibiting proteins. One main problem with the concepts is that the capsules tend to be overgrown by inflammatory cells, with a variation depending on the capsule type. In this study we evaluated the role of Toll-like receptor (TLR) 2 and 4 in the overgrowth reactions against implanted alginate capsules by using transgenic mice lacking TLR2 and TLR4. The F10 generations of KO mice backcrossed in C57Bl/6J phenotype were used and compared with wild type mice. Alginate beads and alginate-poly-L-lysine-alginate (APA) capsules were implanted intra peritoneal in male and female mice (n=5 each group). Animals were sacrificed and the amount of free floating capsules was estimated. In addition, the degree of overgrowth of the free floating capsules was evaluated on a 0-5 score scale. Our data showed that TLR4 KO mice gave significant higher retrieval of implanted APA capsules than wild type in both sexes, while a significant difference was achieved in females for implanted alginate beads. Trends towards higher retrieval rate were seen in TLR2 KO mice, but significant difference to wild type was only seen in male given APA capsules. In TLR4 KO mice, a lower amount of cells were attached to the free floating fraction of alginate beads. These results suggest that TLR4 is a key component in the inflammatory reactions against implanted alginate bioreactors.