TRANSPLANTATION OF MICROCAPSULES (A POTENTIAL BIOARTIFICIAL ORGAN) - BIOCOMPATIBILITY AND HOST-REACTION

Tolerance to alginate-polylysine-alginate microcapsules implanted into the peritoneal cavity was compared in the Wistar Furth rat and the BB/E (Wistar-derived) spontaneously diabetic rat. A marked foreign-body type reaction was observed in the BB/E rat in both diabetic and non-diabetic animals. In contrast, little or no reaction was observed in the Wistar Furth rat. Implantation under the kidney capsule, an immunologically privileged site, did not protect the microcapsules. Blocking the surface charge of the microcapsule by coating with tolylene diisocyanate also failed to modify the reaction. Coating with a water-insoluble lacquer (Eudragit RL) resulted in dense capsule overgrowth. Thus tolerance to alginate polylysine alginate microcapsules appears to be dependent upon the recipient animal strain and this may explain some of the discrepancies in function observed in different animal models when this system has been used to encapsulate pancreatic islets for a bioartificial pancreas. The tissue reaction does not seem to be affected by clinical diabetic status although abnormal immunological responses in animals with a tendency to spontaneous diabetes could be important. Attempts to reduce the reaction to the capsules in the BB/E rat strain by modifying the membrane were unsuccessful.