Inflammatory response to peritoneal implantation of alginate-poly-L-lysine microcapsules

A thorough understanding of the mechanisms involved in the host reaction to alginate-poly-L-lysine microcapsules (HRM) is important to design methods for the evaluation, selection, and development of biocompatible biomaterials and microcapsules or treatments to control this reaction. The objective of this study was to identify those immune cells and cytokines involved in the pathogenesis of the HRM. The total and differential cell counts were evaluated, and the mRNA expression of TNF-alpha, IL-1beta, IL-6 and TGF-beta1 was measured in peritoneal washings at 3, 17, 48, 96 and 168 h after saline or microcapsule injections. Neutrophil number and IL-1beta and IL-6 m-RNA expression presented an early transient increase, with no differences between saline and microcapsule injections, suggesting a reaction to the procedure. Macrophages, lymphocytes and TNF-alpha were significantly more activated over a longer period of time, after microcapsule implantation than saline injection. They are likely involved in transforming the reaction into a chronic inflammatory process. TGF-beta1 and IL-1beta presented a late (day 7) significant increase after microcapsule but not saline injections. They are likely involved in transforming the reaction into a fibrogenic process. These results suggest that macrophages, lymphocytes, TNF-alpha, IL-1beta and TGF-beta1 play a role in the pathogenesis of the HRM.