Diabetic glomerulosclerosis is defined by increased glomerular extracellular matrix (ECM) that is mainly synthesized by mesangial cells that underwent an activation mediated by cytokines and growth factors from various cellular origins. In this study, we tested whether macrophages could infiltrate the glomeruli and influence ECM synthesis in experimental diabetes. To test our hypothesis, we initially studied the dynamics of glomerular macrophage recruitment in streptozotocin-induced diabetic rats at days 1, 2, 4, 8, 15, and 30 by using quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) on isolated glomeruli and immunohistochemistry and morphometry. We then assessed the role of macrophages on the basis of the pharmacological modulation of their recruitment by insulin or ACE inhibitor treatments and by X-irradiation-induced macrophage depletion at days 8 and 30. Macrophages were recruited within the glomeruli at the very early phase of hyperglycemia by using RT-P C R CD14 detection from day 2 and by using ED1 immunohistochemistry from day 8. This glomerular macrophage infiltration was associated with an increase in 1 -chain type IV collagen mRNA. In parallel, the diabetic glomeruli became hypertrophic with an increase in the mesangial area. Macrophage recruitment was preceded by or associated with an increased glomerular expression of vascular cell adhesion molecule 1, intracellular adhesion molecule 1, and monocyte chemoattractant protein 1, which contributes to monocyte diapedesis. Glomerular interleukin-1 mRNA synthesis was also enhanced as early as day 1 and could be involved in the increase in ECM and adhesion molecule gene expressions. Insulin treatment and irradiationinduced macrophage depletion completely prevented the glomerular macrophage recruitment and decreased 1 -chain type IV collagen mRNA and mesangial area in diabetic rats, whereas ACE inhibitor treatment had an incomplete effect. It can be concluded that in the streptozotocin model, hyperglycemia is followed by an early macrophage recruitment that contributes to the molecular and structural events that could lead to glomerulosclerosis. Therefore, besides direct stimulation of mesangial cells by hyperglycemia, macrophages recruited in the glomeruli during the early phase of hyperglycemia could secondarily act on mesangial c e l l s . Diabetes 4 9 :4 6 6-475, 2000

Recent advances indicate that, in various chronic inflammatory disorders, the activation of the immune system is triggered locally rather than in lymphoid organs. In this study, we have evaluated whether the humoral alloimmune response involved in chronic rejection is elicited within the graft. We used the rat aortic interposition model and microdissected the adventitia of the graft. Over time, the T cell infiltrate shifted toward a B helper phenotype. B lymphocyte clusters were detected and were the site of intense proliferation and apoptosis. Simultaneously, adventitial vascular endothelium acquired a high endothelial venule phenotype. Similar features were evidenced in the interstitium of chronically allografts (hearts and kidneys). Strikingly, ganocultured graft interstitial tissue was found to be the site of production of antibodies directed against donor MHC-I molecules. These findings, therefore, document the appearance of germinal centers in chronically rejected tissues. This lymphoid neogenesis implies that the graft is not only the target of the alloimmune response but also a site where this response actually develops, so as to optimize the communication between the targeted tissue and the immune effectors.chronic rejection ͉ transplantation ͉ B cells ͉ germinal centers ͉ adventitia D espite recent advances in transplantation, the long-term outcome of transplanted organs remains impeded by chronic rejection (1). Accumulating evidence suggests that humoral immunity (2-4) and, particularly, alloantibodies directed against donor MHC I molecules (5-8) are critical in the pathogenesis of chronic vascular rejection.Clinically, chronic rejection is responsible for a slow deterioration of graft function, which correlates with typical histological changes. Excluding organ-specific manifestations, the most common histopathological feature is chronic vascular rejection, also known as allograft arteriosclerosis, characterized by widespread and diffuse narrowing of the vascular lumen as a result of intimal proliferation of smooth muscle cells and fibroblasts and destruction of smooth muscle cells from the media (9-12). Chronic vascular rejection is also typified by an abundant adventitial inflammatory infiltrate (9). We therefore evaluated whether the humoral alloimmune response was elicited within the adventitia of the graft. In such case, chronic vascular rejection would be similar to other chronic inflammatory disorders in which tissue destruction results from a vicious circle maintained by an uncontrolled local immune response.We demonstrate the involvement of intragraft lymphoid neogenesis in the development of chronic rejection in an animal model, based on aortic transplantation between histoincompatible strains of rats (13-16). We show that the adventitial inflammatory infiltrate harbors a secondary lymphoid organ structure and that anti-donor MHC I antibodies are produced within these structures. Additionally, we provide insights into the clinical relevance of these observations because similar lymphoid str...

Diabetic nephropathy is a major risk factor for end-stage renal disease and cardiovascular diseases and has a marked genetic component. A common variant (D allele) of the angiotensin Iconverting enzyme (ACE) gene, determining higher enzyme levels, has been associated with diabetic nephropathy. To address causality underlying this association, we induced diabetes in mice having one, two, or three copies of the gene, normal blood pressure, and an enzyme level range (65-162% of wild type) comparable to that seen in humans. Twelve weeks later, the three-copy diabetic mice had increased blood pressures and overt proteinuria. Proteinuria was correlated to plasma ACE level in the three-copy diabetic mice. Thus, a modest genetic increase in ACE levels is sufficient to cause nephropathy in diabetic mice.