Time course of transforming growth factor‐β1 (TGF‐β1) mRNA expression in the host reaction to alginate‐poly‐L‐lysine microcapsules following implantations into rat epididymal fat pads

Microencapsulation of islets of Langerhans within semipermeable membranes has been proposed to prevent their immune destruction after transplantation. However, the successful application of this method is impaired by a pericapsular reaction, which eventually induces graft failure. Our goal is to study the role of cytokines in the pathogenesis of this reaction, using the model of alginate-poly-L-lysine microcapsule implantation into Wistar rat epididymal fat pads (EFP). The specific objective of this study was to determine the time course of transforming growth factor (TGF)-β 1 mRNA expression by semi-quantitative reverse transcriptase-polymerase chain reaction. Microcapsules induced an increase of TGF-β 1 mRNA expression that reached a maximum 14 days after implantation. Seven, 14, 30, and 60 days after microcapsule implantation, the expression of TGF-β 1 mRNA was significantly higher in pericapsular infiltrate cells than in nonimplanted EFP cells (p < 0.05, p < 0.0001, p < 0.005, and p < 0.01, respectively). Injection of physiological saline induced a small and gradual augmentation of TGF-β 1 mRNA expression with a maximum 30 days after injection (p < 0.01 vs. nonimplanted EFP cells). These results demonstrated that microcapsule implantation, in comparison with saline injection, induce an early, extended, and amplified TGF-β 1 mRNA expression. This suggests that TGF-β 1 plays a role in the pathogenesis of the pericapsular host reaction.