Shinji Yaso

Production of monoclonal antibodies to islet cell surface antigens using hybridization of spleen lymphocytes from non-obese diabetic mice.

SummaryNon-obese diabetic mice display a syndrome with dramatic clinical and pathological features similar to those of Type 1 (insulin-dependent) diabetes in man. Circulating autoantibodies to the surface of islet cells were demonstrated in some of these mice by a protein A radioligand assay. To produce monoclonal antibodies to islet cell surface antigens, therefore, we took the spleens of non-obese diabetic mice, transferred the spleen cells into non-immunized recipient mice, which were made immunologically incompetent by a large dose of X-irradiation, and then fused their lymphocytes with FO mouse myeloma cells. After screening the resultant hybrids, one stable hybridoma (3A4) that produced a monoclonal antibody (IgG1) specifically bound to the surface of islet cells was obtained. The purified monoclonal antibody was bound to the surface of transplantable Syrian golden hamster insulinoma cells sevenfold more than control antibody. Adsorption of the antibody on mouse spleen lymphocytes or thymocytes resulted in only a slight decrease in 125I-protein A binding to insulinoma cells. This antibody also reacted with the surface of mouse and rat islet cells, but not with that of rat spleen cells or hepatocytes. A spectrophotometric assay for peroxidase activity demonstrated that six times more peroxidase bound to insulinoma cells incubated with the antibody than to cells treated with control antibody. Furthermore, this antibody could be visually detected in the immunoenzymatic labelling of the surface of insulinoma cells. In summary, we have developed a novel method of producing monoclonal antibodies to the surface of islet cells for probing into the pathogenesis of Type 1 diabetes.

Insulin-degrading enzyme is capable of degrading receptor-bound insulin

In the investigation of the intracellular sites of insulin degradation, it might be important whether receptor-bound insulin could be a substrate for insulin-degrading enzyme (IDE). Insulin receptor and IDE were purified from rat liver using a wheat germ agglutinin column and monoclonal anti-IDE antibody affinity column, respectively. [125I]insulin-receptor complex was incubated with various amounts of IDE at 0 degree C in the presence of disuccinimidyl suberate and analyzed by reduced 7.5% SDS-PAGE and autoradiography. With increasing amounts of IDE, the radioactivity of 135 kd band (insulin receptor alpha-subunit) decreased, whereas that of 110 kd band (IDE) appeared then gradually increased, suggesting that IDE could bind to receptor-bound insulin. During incubation of insulin-receptor complex with IDE at 37 degrees C, about half of the [125I]insulin was dissociated from the complex. However, the time course of [125I]insulin degradation in this incubation was essentially identical to that of free [125I]insulin degradation. Cross-linked, non-dissociable receptor-bound [125I]insulin was also degraded by IDE. Rebinding studies to IM-9 cells showed that the receptor binding activity of dissociated [125I]insulin from insulin-receptor complex incubated with IDE was significantly (p less than 0.001) decreased as compared with that without the enzyme. These results, therefore, show that IDE could recognize and degrade receptor-bound insulin, and suggest that IDE may be involved in insulin metabolism during receptor-mediated endocytosis through the degradation of receptor-bound insulin in early neutral vesicles before their internal pH is acidified.

Possible role of cell surface insulin degrading enzyme in cultured human lymphocytes

SummaryThe kinetic changes of insulin receptors and cell surface insulin degrading enzyme were examined in Bri-7 cultured human lymphocytes after preincubation with or without insulin. The concentration of cell surface insulin degrading enzyme was determined by immunoenzymatic labeling method using a polyclonal antiserum to insulin degrading enzyme. In Bri-7 cells preincubated with 10−10 to 10−5mol/l insulin for 18h, the surface insulin receptors and insulin degrading enzyme decreased progressively as a function of the concentration of insulin in the preincubation medium. The surface insulin receptors and insulin degrading enzyme of cells preincubated with 10−6mol/l insulin were decreased to 25 and 35% of the control respectively. In Bri-7 cells preincubated with 10−6 mol/l insulin for 30 min to 18 h, the loss of surface insulin degrading enzyme was slightly slower than that of the receptors; however, the curves were essentially parallel to each other. Thus, the treatment of Bri-7 cells with insulin caused down-regulation of insulin receptors in a dose- and time-dependent manner. Cell surface insulin degrading enzyme also decreased simultaneously. A combination of several insulin degradation assays (trichloroacetic acid precipitation, gel filtration and receptor rebinding) demonstrated that cell surface bound insulin remained intact, and that the degradation in Bri-7 cells seemed to be a limiting proteolysis of insulin. Furthermore, by the receptor rebinding method insulin degrading activity in cells after preincubation with 10−6 mol/l insulin (19.6±4.6%) was decreased, although not significantly, as compared with cells after preincubation without insulin (24.6±4.8%). These results suggest a possible hypothesis that cell surface insulin degrading enzyme may be internalized with the insulin-receptor complex, and that it may degrade insulin during the intracellular process.

Effect of antiserum to monoclonal anti-islet cell surface antibody on pancreatic insulitis in non-obese diabetic mice

Immunotherapeutic intervention has been studied in non-obese diabetic (NOD) mice. Twenty-five male NOD mice aged 6 weeks were treated with anti-mouse T lymphocyte serum (ATS), N-(2-carboxyphenyl)-4-chloroanthranilic acid disodium salt (CCA); a non-specific immunostimulant which seems to potentiate the suppressor T cell activity, and antiserum raised against previously reported monoclonal antibody 3A4 to the surface of islet cells. Pancreatic islets from NOD mice sacrificed at 12 weeks of age were scored morphologically for the severity and the frequency of insulitis. Both the severity of insulitis in each islet and the frequency of insulitis-positive islets in each pancreas were reduced in the groups treated with ATS (group B), antiserum to 3A4 (group D) and a combination of antiserum plus CCA (group E) in comparison with other groups (control: group A and CCA: group C). At 8 weeks of age, the binding capacities of sera to insulinoma cells measured by protein A radioligand assay were significantly decreased in the groups treated with antiserum to 3A4 (groups D and E) as compared with those in the other groups. These results suggest that both ATS and antiserum to 3A4 prevent the occurrence and the progress of insulitis in NOD mice, but the immunosuppressive mechanisms differ from each other; therefore, combination therapy with these suppressants may be more effective in the prevention of Type 1 diabetes mellitus.

Suppressor T-cell abnormality in NOD mice before onset of diabetes

To investigate the pathological role of suppressor T-cells in non-obese diabetic (NOD) mice, we stimulated splenic T-lymphocytes from diabetes-prone NOD mice with concanavalin A (ConA) and then evaluated their ability to suppress the lymphocyte-proliferative responses to mitogen and allogenic cells. Lymphocytes from NOD mice showed significantly less suppressor ability than did those from BALB/c mice and non-obese non-diabetic (NON) mice, the corresponding non-diabetic sister strain of the NOD mouse, both in the mitogen response and in the mixed lymphocyte reaction (MLR). We used monoclonal antibodies and flow cytometry to analyze the lymphocytic surface phenotypes, and found markedly fewer Lyt2+ T-lymphocytes (suppressor/cytotoxic T-lymphocyte) in the NOD mice than in both controls after exposure to ConA. These results suggest that suppressor T-cell activity is already depressed in NOD mice before diabetes begins and that a substantial decrease in the number of suppressor T-cells induced by ConA may explain this depressed suppressor activity. This impairment may contribute to the pathogenesis of type 1 diabetes in NOD mice.

CELLULAR IMMUNE DYSFUNCTION IN THE NOD MOUSE

It is generally accepted that T lymphocyte-mediated autoimmunity contributes to the pathogenesis of Type 1 diabetes in humans and animals. Using spleen cells from nonobese diabetic (NOD) mice, a model of human Type 1 diabetes, we have analyzed the subset of T lymphocytes by flow cytometry and investigated concanavalin A (Con A)-induced interleukin 2 (IL-2) production and cell proliferation. NOD mice showed a higher percentage of Thy1.2+, L3T4+, and Lyt2+ T lymphocytes than did control ICR mice through the whole age examined. Spleen cells from a large majority of NOD mice were found to generate very low IL-2 production and cell proliferation in response to Con A. However, a few mice preserved their responsiveness to Con A. The following reasons may indicate that macrophage-mediated suppression participates in the deficient function of NOD spleen cells. (a) Macrophage depletion from NOD spleen cells retrieved Con A-induced IL-2 production. (b) Thioglycollate-induced peritoneal exudate cells containing many activated macrophages could completely suppress cell proliferation. (c) Prostaglandin synthetase inhibitor indomethacin reversed the suppression of IL-2 production by macrophages. (d) Conversely, exogenous prostaglandins could show the partial suppression of IL-2 production. These results suggest that activated macrophages suppress the response of NOD spleen cells to Con A mostly through prostaglandins. This impairment may contribute to the pathogenesis of Type 1 diabetes in NOD mice.