Filippo Calcinaro

CTLA-4-Ig regulates tryptophan catabolism in vivo.

Cytotoxic T lymphocyte–associated antigen 4 (CTLA-4) plays a critical role in peripheral tolerance. However, regulatory pathways initiated by the interactions of CTLA-4 with B7 counterligands expressed on antigen-presenting cells are not completely understood. We show here that long-term survival of pancreatic islet allografts induced by the soluble fusion protein CTLA-4–immunoglobulin (CTLA-4–Ig) is contingent upon effective tryptophan catabolism in the host. In vitro, we show that CTLA-4–Ig regulates cytokine-dependent tryptophan catabolism in B7-expressing dendritic cells. These data suggest that modulation of tryptophan catabolism is a means by which CTLA-4 functions in vivo and that CTLA-4 acts as a ligand for B7 receptor molecules that transduce intracellular signals.

Demonstration of a Dawn Phenomenon in Normal Human Volunteers

To ascertain whether the dawn phenomenon occurs in nondiabetic individuals and, if so, whether it is due to an increase in glucose production or a decrease in glucose utilization, we determined plasma concentrations of glucose, insulin, C-peptide, and counter regulatory hormones, as well as rates of glucose production, glucose utilization, and insulin secretion at one-halfhourly intervals between 1:00 and 9:00 a.m. in eight normal volunteers. After 5:30 a.m., plasma glucose, insulin, and C-peptide concentrations all increased significantly; rates of glucose production, glucose utilization, and insulin secretion also increased (all P < 0.05). Plasma cortisol, epinephrine, and norepinephrine increased significantly from nocturnal nadirs between 4:00 and 6:30 a.m. Plasma growth hormone, which had increased episodically between 1:00 and 4:30 a.m., decreased thereafter nearly 50% (P < 0.05). Plasma glucagon did not change significantly throughout the period of observation. These results indicate that a dawn-like phenomenon, initiated by an increase in glucose production, occurs in nondiabetic individuals. Thus, early morning increases in plasma glucose concentrations and insulin requirements observed in IDDM and NIDDM may be an exaggeration of a physiologic circadian variation in hepatic insulin sensitivity induced by antecedent changes in catecholamine and/or growth hormone secretion.

Studies on overnight insulin requirements and metabolic clearance rate of insulin in normal and diabetic man: relevance to the pathogenesis of the dawn phenomenon

SummaryIn order to assess whether the metabolic clearance of insulin changes overnight, 11 patients with Type 1 (insulin-dependent) diabetes and low insulin antibody titre, and 6 nondiabetic subjects were studied. In these studies insulin was always infused by a Harvard pump. Initially, the nocturnal insulin requirements were assessed in the diabetic patients by an overnight feedback insulin infusion to maintain euglycaemia. The insulin requirements decreased continuously after midnight to a nadir of 0.115 ± 0.014 mU · kg−1 · min−1 at 04.30 hours, but after 05.00 hours the insulin requirements increased nearly 40 percent to a maximum of 0.16 ±0.012 mU · kg−1 · min−1 at 07.00 hours. To assess whether plasma insulin clearance changes overnight, the diabetic patients were studied on two different occasions, from 22.00–02.30 hours and from 04.00–08.30 hours. During each of these two studies insulin was infused in sequential steps of 90 min each at the rate of 0.13, 0.40 and 0.20 mU · kg−1 · min−1. Despite changes in plasma free insulin concentration, the metabolic clearance of insulin in the interval 22.00–02.30 hours (12.6±0.17 ml · kg−1 · min−1) was no different from that of the interval 04.00–08.30 hours (12.5 ± 0.19 ml · kg−1 · min−1). The nondiabetic subjects were studied on two different occasions to assess whether the metabolic clearance of insulin changes overnight. Somatostatin (0.25 mg/h) and insulin (0.3 mU kg−1 · min−1) were infused from 22.00–02.30 hours on one occasion, and from 04.00–08.30 hours on the other. The metabolic clearance of plasma free insulin in the interval 22.00–02.30 hours was no different from that of the interval 04.00–08.30 hours (12.6 ± 0.20 vs 12.9 ± 0.25 ml · kg−1 · min−1 nor was it different from that of the diabetic patients.It is concluded that, first, the metabolic clearance rate of insulin does not change overnight either in diabetic or in nondiabetic subjects; second, that it is independent of plasma insulin concentration; and third, that its value is comparable in nondiabetic subjects and in diabetic patients with a low titre of insulin antibodies. Thus, changes in insulin sensitivity rather than changes in insulin clearance are implicated in the pathogenesis of the dawn phenomenon.

A method for the massive separation of highly purified, adult porcine islets of langerhans

A method for the massive and reproducible isolation of highly purified, adult porcine islets of Langerhans is described. The successful combination of donor animal-strain selection with original procedures for pancreas retrieval and enzymatic digestion permitted us to separate uniquely massive concentrations of pure porcine islets with no need for mechanical disruption of the pancreatic tissue. Following our procedure, porcine islets, which fully retain viability and function, can be harvested easily and rapidly. Xenotransplantation of such islets, immunoprotected within algin/polyaminoacidic microcapsules, was associated with complete reversal of hyperglycemia in rodents with either spontaneous or streptozotocin-induced diabetes mellitus.

Immunoprotection of pancreatic islet grafts within artificial microcapsules.

To circumvent pancreatic islet graft-directed immune destruction we enveloped porcine islets within highly biocompatible and selectively permeable algin/polyaminoacid microcapsules. These special microspheres were deposited between the inner (permeable) and the outer (impermeable) layers of an artificial, coaxial vascular prosthesis, directly anastomized to blood vessels. Five dogs with spontaneous, insulin-dependent diabetes received microencapsulated porcine islets in arterio-vein iliac prosthesis by-passes. One showed complete and the remainder partial, sustained reversal of hyperglycemia. Microencapsulation may be a potential solution to immunological problems related to islet transplantation.

Improved in planta expression of the human islet autoantigen glutamic acid decarboxylase (GAD65)

The smaller isoform of the enzyme glutamic acid decarboxylase (GAD65) is a major islet autoantigen in autoimmune type 1 diabetes mellitus (T1DM). Transgenic plants expressing human GAD65 (hGAD65) are a potential means of direct oral administration of the islet autoantigen in order to induce tolerance and prevent clinical onset of disease. We have previously reported the successful generation of transgenic tobacco and carrot that express immunoreactive, full-length hGAD65. In the present study, we tested the hypothesis that the expression levels of recombinant hGAD65 in transgenic plants can be increased by targeting the enzyme to the plant cell cytosol and by mediating expression through the potato virus X (PVX) vector. By substituting the NH2-terminal region of hGAD65 with a homologous region of rat GAD67, a chimeric GAD671-87/GAD6588-585 molecule was expressed in transgenic tobacco plants. Immunolocalization analysis showed that immunoreactive GAD67/65 was found in the plant cell cytosol. By using a radio-immuno assay with human serum from a GAD65 autoantibody-positive T1DM patient, the highest expression level of the recombinant GAD67/65 protein was estimated to be 0.19% of the total soluble protein, compared to only 0.04% of wild-type hGAD65. Transient expression of wild-type, full-length hGAD65 in N. benthamiana mediated by PVX infection was associated with expression levels of immunoreactive protein as high as 2.2% of total soluble protein. This substantial improvement of the expression of hGAD65 in plants paves the way for immunoprevention studies of oral administration of GAD65-containing transgenic plant material in animal models of spontaneous autoimmune diabetes.

Transgenic plants expressing human glutamic acid decarboxylase(GAD65), a major autoantigen in insulin-dependent diabetes mellitus

Parenteral and oral administration of autoantigens can induce immune tolerance in autoimmune diseases. Prophylactic therapy based on oral administration of human autoantigens is not, however, feasible when sufficient quantities of candidate autoantigens are not available. Transgenic plants that express high levels of recombinant proteins would allow large quantities of autoantigens to be produced at relatively low costs. In addition, transgenic food would provide a simple and direct method of delivering autoantigens. The production and the characterization of transgenic tobacco and carrot plants expressing human GAD65, a major autoantigen in human insulin-dependent diabetes mellitus (IDDM), is reported. Immunogold labeling and electron microscopy of transgenic tobacco tissue shows the selective targeting of human GAD65 to chloroplast tylacoids and mitochondria. In planta expressed GAD65 has a correct immunoreactivity with IDDM-associated autoantibodies and retains enzymatic activity, a finding that suggests a correct protein folding. In transgenic tobacco and carrot the expression levels of human GAD65 varies between 0.01% and 0.04% of total soluble proteins. Transgenic edible plant organs are now available to study the feasibility of inducing immune tolerance in IDDM animals by oral administration of GAD65.

PROTECTION FROM AUTOIMMUNE DIABETES BY ADJUVANT THERAPY IN THE NON-OBESE DIABETIC MOUSE : THE ROLE OF INTERLEUKIN-4 AND INTERLEUKIN-10

Insulin‐dependent diabetes mellitus (IDDM) is an autoimmune disease that is characterized by the destruction of insulin‐producing β‐cells in the pancreatic islets. A single administration of CFA prevents clinical hyperglycaemia in non‐obese diabetic (NOD) mice. We have previously shown that CFA administration does not eliminate insulitis in the pancreas of the treated animals, but diverts the disease process from a destructive to a non‐destructive pathway. We provide evidence that this phenomenon may be under cytokine control. Neutralizing monoclonal antibodies against IL‐4 and IL‐10 were injected, singularly or in combination, into CFA‐treated NOD mice. Antibody treatment did not lead to the development of overt diabetes; however, a marked impairment of glucose tolerance was shown in about one half of the mice treated with a combination of the two antibodies at the end of the study. This functional abnormality correlated with the histological loss of pancreatic islet tissue. These studies suggest a role for IL‐4 and IL‐10 in CFA‐induced protection from diabetes in the NOD mouse. They also suggest that, in this animal model, the nature of the autoimmune response to islet tissue (either destructive or non‐destructive) may reflect the relative proportion of Th1‐ and Th2‐type cytokines produced in the lesions.

Autoantibody Profile and Epitope Mapping in Latent Autoimmune Diabetes in Adults

Abstract: The presence of islet cell autoantibodies in adult diabetic subjects who do not require insulin treatment for at least six months after the initial clinical diagnosis identifies the so‐called latent autoimmune diabetes in the adult (LADA). Glutamic acid decarboxylase autoantibodies (GAD65Ab) are the best immune marker to identify LADA patients, while other islet autoantibodies, such as IA‐2 autoantibodies, have a very low diagnostic sensitivity. Islet cell antibodies, as detected by indirect immunofluorescence, may improve the diagnostic specificity of the immune analysis when detected in GAD65Ab‐positive patients. Although the majority of LADA patients progresses towards insulin dependency within a few years after the diagnosis, this form of diabetes is heterogeneous. The presence of high titers of GAD65Ab and/or GAD65Ab directed towards COOH‐terminal epitopes of the autoantigen (GAD65‐CAb) identifies a subgroup of LADA patients with clinical characteristics similar to those of typical type 1 diabetes and at very high risk of progression toward insulin dependency. On the other hand, low titers of GAD65Ab, or the exclusive presence of GAD65Ab directed to middle epitopes of the autoantigen, characterizes LADA patients with clinical characteristics almost indistinguishable from those of GAD65Ab‐negative type 2 diabetic patients. LADA subjects, especially in the presence of high titers of GAD65Ab and/or GAD65‐CAb, have an increased risk for other organ‐specific autoimmune diseases such as thyroid autoimmune diseases or autoimmune Addisons. LADA should be considered a major component of the autoimmune polyendocrine syndromes, and screening for other autoimmune diseases should be performed in all LADA patients.

Recent advances in adrenal autoimmunity

Autoimmune Addison’s disease (AAD) results from the immune-mediated destruction of adrenocortical cells. AAD is a major component of the autoimmune polyendocrine syndromes type 1 (APS 1) and type 2. The adrenal autoimmune process is made evident by the apperance of circulating autoantibodies against the steroidogenic enzyme 21-hydroxylase. Detection of 21-hydroxylase in patients with endocrine autoimmune diseases enables the identification of subjects with preclinical AAD. An impaired response to a corticotrophin stimulation test marks the irreversible stage of preclinical AAD and predicts progression towards clinical AAD in over 80% of cases. APS 1 is caused by mutations of the autoimmune regulator (AIRE) gene, which encodes an activator of transcription, Aire, that induces the expression of autoantigens in thymic medullary epithelial cells and promotes immunological tolerance. Isolated and APS 2-related AAD is an autoimmune disease with evidence for complex genetic susceptibility caused by T-cell-mediated destruction of adrenocortical cells, with a major contribution of HLA genes. The target cells in the adrenal cortex participate in the immune reaction by releasing chemokines, such as CXCL-10, that attract Th1 cells.