Pre-diabetes in the spontaneously diabetic BB/E rat: lymphocyte subpopulations in the pancreatic infiltrate and expression of rat MHC class II molecules in endocrine cells.

Use of monoclonal antibodies specific for rat lymphocyte subsets and an anti-insulin marker has allowed us to document the following sequence of events leading to the development of clinical diabetes in this animal model. The first change observed in the pancreas is increased expression of MHC class II molecules on vascular endothelium and this precedes lymphocytic infiltration. Next, T cells of the T helper phenotype infiltrate the pancreas around blood vessels. Many of the infiltrating T cells show class II expression indicating that they are activated. A few cytotoxic and suppressor cells and B lymphocytes are also present and their numbers increase proportionately with rat age. Some macrophages are also seen. Finally, at a late stage class II MHC molecules can be detected in partially destroyed islets on beta cells which are still actively synthesising insulin. We have never observed expression of class II molecules on glucagon or somatostatin secreting cells which are invariably well preserved.