Immune response to xenogeneic matrix grafts used in pediatric surgery

Lyoplant is an acellular, bovine derived extracellular matrix (ECM) that has been used for tissue remodelling and repair in numerous xenotransplantations. The aim of our study was to evaluate the inflammatory response and tensile strength after xenogeneic matrix (Lyoplant) implantation compared to the more widely used synthetic polypropylene matrix.

Full-thickness abdominal wall defects were created in 15 Wistar WU rats and reconstructed with either a Lyoplant matrix (B. Braun Aesculap, Tuttlingen, Germany) or a Prolene matrix (a polypropylene matrix [PPP]; Prolene, Ethicon, Norderstedt, Germany). Animals in both the treatment and the control groups were checked daily for local and systemic complications. Bodyweight was recorded and the possible development of a hernia was monitored. After 6 weeks the abdomen was reopened and adhesions to the intestine were determined. Histopathology and immunohistochemistry were performed to evaluate the immunological reaction to the xenograft.

Compared to the untreated animals, all rats had a physiological growth and bodyweight curve: No wound infection was observed during the experiment. An abdominal hernia developed at the implant site only in one rat treated with a PPP matrix. All other animals had an excellent clinical recovery and good cosmetic results. PPP animals showed a pronounced inflammatory response indicated by an increased number of fibroblasts. The Lyoplant matrix implantation induced an infiltration of CD4 and CD68 positive cells. In addition, active neovascularization was found, indicating a remodelling process. The inflammatory response in Lyoplant treated animals was significantly milder than in PPP implanted rats. Interestingly, some CD8 positive cells were detected in the Lyoplant group.

A xenogeneic extracellular matrix, such as Lyoplant, may induce an immune response which is predominantly TH2-like and comparable with a remodelling reaction rather than rejection.