Observations on rat collagenase-separated islets and long-term composite islet allografts

Collagenase digest preparations of isolated rat islets and long-surviving allogeneic rat islets implanted beneath the kidney capsule of a composite kidney and islet allograft have been studied immunocytochemically and by electron microscopy. The four main endocrine cell types were identified in the collagenase preparations with minimal evidence of cell damage. In contrast, there were only granulated B cells in the composite grafts and amongst the granules of these cells there was pleomorphism. The granule appearances may support previous suggestions that paracrine control of insulin secretion is lacking in these composite grafts.