Appearance of Cells Expressing CD80 and CD86 Costimulatory Antigens in the Pancreas of Nonobese Diabetic Mice

The immunopathogenetic mechanisms that lead to type I diabetes in the nonobese diabetic mouse are poorly defined. The immunoregulatory effects of the costimulatory CD80/B7-1 and CD86/B7-2 antigens expressed by the antigen-presenting cells may be crucial for the development of immune responses and their absence may lead to clonal anergy, which is important in the prevention of autoimmune reactivity. To evaluate the role of the CD80 and CD86 antigens in the development of insulin-dependent diabetes mellitus, expression of these antigens in the pancreas of normal and nonobese diabetic mice was studied. The pancreata of normal BALB/c mice and young nonobese diabetic mice contained no CD80- or CD86-positive cells. CD80- and CD86-positive cells appeared in the pancreas of nonobese diabetic mice by 6 weeks of age. Double immunostaining at the age of 12 weeks showed that CD80-positive cells accumulated around the islets of Langerhans but no insulin-containing cells expressed the costimulatory molecules. The morphology of the CD80- and CD86-positive cells was heterogeneous. Many were Mac-1 integrin (CD11b/CD18) positive, suggesting that macrophages expressing the costimulatory antigens are present in the pancreas of all nonobese diabetic mice by 12 weeks of age and that CD80- and CD86-expressing macrophages may be involved in the local regulation of antiislet immune responses.