In vivo microscopy of murine islets of Langerhans: increased adhesion of transferred lymphocytes to islets depends on macrophage-derived cytokines ina model of organ-specific insulitis

Environmental factors contribute to the pathogenesis of type 1 diabetes (in sulin-dependent diabetes mellitus). Multiple low doses of streptozotocin (M LDS) induce hyperglycaemia and insulitis in mice. Previously we demonstrate d that adhesion of lymphocytes to endothelium of islets is only increased w hen donor animals were diabetic and recipient mice had received 5 mg/kg str eptozotocin (STZ). Therefore we used streptozotocin to evaluate the immunol ogical relevance of such an irritation of islets. Lymphocytes, separated fr om diabetic mice (MLDS), were fluorescently labelled and injected to recipi ent mice that had received 5 mg/kg STZ. With in vivo microscopy we measured lymphocyte flow and adherence in islets. Expression of vascular cell adhes ion molecule-1 (VCAM-1) and intracellular adhesion molecule-1 (ICAM-1) in t he pancreas was assessed using immunohistochemistry. Very late antigen-4 (V LA-4) and leucocyte function-associated antigen-1 (LFA-1) expression on tra nsferred lymphocytes was measured with flow cytometry. Pretreatment of reci pients with antibodies to cytokines or silica reduced lymphocyte adherence to islet endothelium from 2.04% (goat immunoglobulin G; IgG) or 1.82% (rat IgG) to 0.47, 0.58, 0.39 or 0.19% for monoclonal antibody (mAb) interferon- gamma (IFN-gamma), polyclonal antibody (pAb) tumour necrosis factor-alpha ( TNF-alpha), pAb interleukin (IL)-1 alpha or silica, respectively. Reduced a dhesion was associated with a decreased expression of VCAM-1 and ICAM-1 in islets of treated recipients compared with mice treated with 5 mg/kg STZ al one. In conclusion, pretreatment of recipients with 5 mg/kg STZ leads to an increased expression of adhesion molecules in the islets and lymphocyte ad hesion to islet endothelium in vivo, demonstrating an immune response of th e islets. Prevention of increased expression of ICAM-1 or VCAM-1 and reduct ion of lymphocyte adhesion in islets by silica or antibody indicate an invo lvement of macrophages and macrophage derived cytokines in the generation o f this immune response.