Insulitis in human diabetes: a histological evaluation of donor pancreases.AIMS/HYPOTHESIS
 According to the consensus criteria developed for type 1 diabetes, an individual can be diagnosed with insulitis when ≥ 15 CD45+ cells are found within the parenchyma or in the islet-exocrine interface in ≥ 3 islets.  The aim of this study was to determine the frequency of individuals with type 2 diabetes fulfilling these criteria with reference to non-diabetic and type 1 diabetic individuals.


 Insulitis was determined by examining CD45+ cells in the pancreases of 50, 13 and 44 organ donors with type 2 diabetes, type 1 diabetes and no diabetes, respectively.  CD3+ cells (T cells) infiltrating the islets were evaluated in insulitic donors.  In insulitic donors with type 2 diabetes, the pancreases were characterised according to the presence of CD68 (macrophages), myeloperoxidase (MPO; neutrophils), CD3, CD20 (B cells) and HLA class I hyperstained islets.  In all type 2 diabetic donors, potential correlations of insulitis with dynamic glucose-stimulated insulin secretion in vitro or age, BMI, HbA1c or autoantibody positivity were examined.


 Overall, 28% of the type 2 diabetic donors fulfilled the consensus criteria for insulitis developed for type 1 diabetes.  Of the type 1 diabetic donors, 31% fulfilled the criteria.  None of the non-diabetic donors met the criteria.  Only type 1 diabetic donors had ≥ 15 CD3+ cells in ≥ 3 islets.  Type 2 diabetic donors with insulitis also had a substantial number of CD45+ cells in the exocrine parenchyma.  Macrophages constituted the largest fraction of CD45+ cells, followed by neutrophils and T cells.  Of type 2 diabetic pancreases with insulitis, 36% contained islets that hyperstained for HLA class I. Isolated islets from type 2 diabetic donors secreted less insulin than controls, although with preserved dynamics.  Insulitis in the type 2 diabetic donors did not correlate with glucose-stimulated insulin secretion, the presence of autoantibodies, BMI or HbA1c.


 CONCLUSIONS/INTERPRETATION
 The current definition of insulitis cannot be used to distinguish pancreases retrieved from individuals with type 1 diabetes from those with type 2 diabetes.  On the basis of our findings, we propose a revised definition of insulitis, with a positive diagnosis when ≥ 15 CD3+ cells, not CD45+ cells, are found in ≥ 3 islets.
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