Further morphological and biochemical observations on early low dose streptozocin diabetes in mice

Conflicting published data regarding the role of macrophages and other cell types during the early stages of diabetes mellitus led us to further study this problem. To this end we diabetized mice, using low doses of streptozocin (STZ), 40 mg/kg body wt/day/5 days, and processed their pancreatic tissue for immunocytochemistry and ultrastructural observations; immunohistochemistry was performed on days 5 and 18 after the first STZ injection, and islets were observed ultrastructurally on days 5, 9, 10, and 18. Animals were tested for fasting serum glucose, and isolated islets were assayed for insulin secretion capacity. Immunohistology demonstrated that expression of major histocompatability complex class 2 antigens is strongly induced by multiple, low dose STZ treatments prior to impaired insulin release, and that different types of cells within the islet are capable of expressing Ia molecules. Ultrastructurally we found (a) a small number of macrophages (most probably resident monocytes/macrophages) containing B-cell debris, that were located close to either damaged or intact B cells; (b) a large number of recruited macrophages in a vascular or perivascular position; and (c) macrophages recognizable in the exocrine portion, close to the islets, occasionally containing exocrine cell debris. This led us to believe that recruited macrophages play an important role in the early islet-infiltrating stage.