Level of major histocompatibility complex class I expression on endothelium in non-obese diabetic mice influences CD8 T cell adhesion and migration

An important prerequisite for development of insulitis and beta-cell destruction in type 1 diabetes is successful transmigration of autoreactive T cells across the islet endothelium. Previous work suggests that antigen presentation to T cells by endothelium, which requires endothelial cell expression of major histocompatibility complex (MHC) molecules, promotes tissue-specific T cell migration. We therefore tested the hypothesis that the level of endothelial MHC class I molecule expression in diabetes-prone mice directly influences autoreactive CD8 T cell migration. We investigated the immune phenotype of endothelial cells, focusing on endothelial MHC class I molecule expression in a range of different tissues and mouse strains, including non-obese diabetic (NOD) mice. In addition, we examined whether the level of expression of MHC class I molecules influences autoantigen-driven CD8 T cell transmigration. Using endothelial cell lines that expressed 'high' (NOD mouse), medium (NOD x C3H/HeJ F(1) generation mice) and no (C3H/HeJ) H-2K(d), we demonstrated in vitro that MHC levels have a profound effect on the activation, adhesion and transmigration of pathogenic, islet autoreactive CD8 T cells. The expression level of MHC class I molecules on endothelial tissues has a direct impact upon the efficiency of migration of autoreactive T cells. The immune phenotype of microvascular endothelium in NOD mice may be an additional contributory factor in disease predisposition or development, and similar phenotypes should be sought in human type 1 diabetes.

Proinsulin peptide immunotherapy in type 1 diabetes: report of a first-in-man Phase I safety study

Immunotherapeutic strategies under consideration for type 1 diabetes include modification of the autoimmune response through antigen-specific routes. Administration of short peptides representing T cell epitopes targeted by patients with the disease represents one approach. This study evaluated safety and mechanistic outcomes during first-in-man intradermal administration of a human leucocyte antigen-DR4 (HLA-DR4)-restricted peptide epitope of proinsulin (C19-A3). This randomized, open-label study assessed two major theoretical risks of peptide immunotherapy, namely induction of allergic hypersensitivity and exacerbation of the proinflammatory autoimmune response, using clinical assessment and mechanistic assays in vitro. Patients with long-standing type 1 diabetes and HLA-DRB1*0401 genotype received 30 microg (n = 18) or 300 microg (n = 18) of peptide in three equal doses at 0, 1 and 2 months or no intervention (n = 12). Proinsulin peptide immunotherapy in the dosing regimen used is well tolerated and free from risk of systemic hypersensitivity and induction/reactivation of proinsulin-specific, proinflammatory T cells. Peptide-specific T cells secreting the immune suppressive cytokine interleukin (IL)-10 were observed at month 3 in four of 18 patients in the low-dose group (versus one of 12 in the control group; P = not significant). Mean IL-10 response to peptide in the low-dose group increased between 0 and 3 months (P = 0.05 after stimulation with 5 microM peptide in vitro) and then declined to baseline levels between 3 and 6 months (P = 0.01 at 10 microM peptide in vitro). These studies pave the way for future investigations in new-onset patients designed to examine whether proinsulin peptide immunotherapy has beneficial effects on markers of T cell autoimmunity and preservation of beta cell mass.

Primary and immortalised human pancreatic islet endothelial cells: phenotypic and immunological characterisation

AIMS/HYPOTHESIS

Studies on the biology of the microvascular endothelial cells (MECs) that surround and penetrate the pancreatic islets are hampered by difficulties in isolating and culturing large numbers of pure cells. We aimed to morphologically and functionally characterise primary MECs purified and cultured from human islets, and to establish a simian virus 40 (SV40)-immortalised cell line from these primary cultures.

MATERIALS AND METHODS

Human islet MECs were extracted and purified using anti-CD105 coated immunomagnetic beads, and endothelial markers and surface molecules analysed by flow cytometric analysis. An immortalised cell line was then established by using a chimeric adeno5/SV40 virus.

RESULTS

Islet MECs expressed classic and specific endothelial markers, a high basal level of intercellular adhesion molecule-1, and low levels of E-selectin and TNF (previously known as TNF-alpha) inducible vascular cell adhesion molecule-1. IFNG (previously known as IFN-gamma) induced expression of HLA class II molecules. The immortalised islet MECs expanded rapidly, exhibited increased DNA synthesis, and were passaged approximately 30 times, without signs of senescence. They retained the endothelial characteristics of the parental cells, and behaved as the primary cells in terms of TNF stimulation of expression of adhesion molecules and support of leucocyte adhesion and transmigration.

CONCLUSIONS/INTERPRETATION

The immortalised islet MECs that we have established could effectively represent a substitute for primary counterparts for in vitro studies on the role of the microvasculature in pathophysiological processes involved in type 1 and type 2 diabetes.

Expression of nephrin by human pancreatic islet endothelial cells

AIMS/HYPOTHESIS

The islet microcirculation has morphological characteristics resembling those of renal glomeruli. Transcription of the nephrin gene, a highly specific barrier protein of the slit diaphragm of podocyte foot processes, has been reported in the pancreas, although its cellular localisation and function remain to be defined. In this study, we purified and characterised microvascular endothelial cells (MECs) isolated from human islets and investigated the expression and distribution of nephrin on these cells.

METHODS

Human islet MECs were extracted and purified using anti-CD105-coated immunomagnetic beads and their endothelial characteristics were confirmed by expression of classical endothelial markers and basal high-level expression of intercellular adhesion molecule-1 and TNF-alpha-inducible vascular cell adhesion molecule-1. Nephrin expression was assessed by immunofluorescence, flow cytometric analysis and western blotting on cell lysates, as well as by RT-PCR.

RESULTS

Immunofluorescence studies detected nephrin in a fine, punctate, diffuse pattern on cultured islet MECs, and also in human pancreatic islet sections. In both cases nephrin colocalised with endothelial markers. TNF-alpha treatment induced a marked reduction and redistribution of the protein in one or multiple aggregates. Nephrin expression was confirmed by flow cytometry, western blotting and RT-PCR studies. In contrast, nephrin could not be detected at the protein or mRNA level in human macro- and microvascular cells from other sites.

CONCLUSIONS/INTERPRETATION

Nephrin is expressed at protein and mRNA levels in islet microendothelium, supporting the hypothesis that islet MECs exhibit distinctive morphological characteristics that indicate functional specialisation of potential pathophysiological importance.