In vitro activation of human macrophages by alginate-polylysine microcapsules

Microencapsulated islets of Langerhans have been proposed as a bioartificial pancreas. However, foreign body reaction with fibrosis has been observed around implanted microcapsules. Since macrophages are present in this reaction and interleukin-1 (IL-1), a cytokine released by activated macrophages, may induce fibrosis, we tested the capacity of alginate-polylysine microcapsules to activate macrophages. Human monocytes were isolated from whole blood of healthy donors by a Ficoll density gradient and adherence to a plastic support. Monocytes were cultured for 24 h with: (1) alginate-polylysine microcapsules; (2) lipopolysaccharide (LPS) (positive control group); and (3) alone (negative control group). Monocyte activation was evaluated by measuring the secretion of IL-1 beta and the production of intracellular IL-1 alpha and IL-1 beta. Macrophages characterization was performed by immunocytological subtyping. IL-1 beta release and intracellular IL-1 beta and IL-1 alpha production were significantly higher when macrophages were cultured with alginate-polylysine microcapsules than when macrophages were cultured alone. In conclusion, macrophages are activated in vitro by alginate-polylysine microcapsules. This effect may be involved in the fibrosis observed in vivo around implanted microcapsules. In addition, interleukin-1, released during macrophage activation, may cross the microcapsule membrane and impair islet function.