Disordered cellular immunity in type I diabetes of man and the BB rat

Mechanisms of autoimmunity in the non-obese diabetic mouse: effector/regulatory cell equilibrium during peak inflammation

Immune imbalance in autoimmune disorders such as type 1 diabetes may originate from aberrant activities of effector cells or dysfunction of suppressor cells. All possible defective mechanisms have been proposed for diabetes-prone species: (i) quantitative dominance of diabetogenic cells and decreased numbers of regulatory T cells, (ii) excessive aggression of effectors and defective function of suppressors, (iii) perturbed interaction between effector and suppressor cells, and (iv) variations in sensitivity to negative regulation. The experimental evidence available to date presents conflicting information on these mechanisms, with identification of perturbed equilibrium on the one hand and negation of critical role of each mechanism in propagation of diabetic autoimmunity on the other hand. In our analysis, there is no evidence that inherent abnormalities in numbers and function of effector and suppressor T cells are responsible for the immune imbalance responsible for propagation of type 1 diabetes as a chronic inflammatory process. Possibly, the experimental tools for investigation of these features of immune activity are still underdeveloped and lack sufficient resolution, in the presence of the extensive biological viability and functional versatility of effector and suppressor elements.

Assessment of the diabetogenic drugs alloxan and streptozotocin as models for the study of immune defects in diabetic mice

The efficacy of the diabetogenic drugs streptozotocin and alloxan were evaluated as models for the study of immune defects associated with diabetes. Streptozotocin- or alloxan-treated mice, with a stable hyperglycaemia of 25-33 mmol/l plasma glucose, were severely impaired in their ability to mount antibody forming, mitogenic, or delayed-type hypersensitivity responses in vivo. Treatment of alloxan-diabetic mice with insulin in vivo completely reversed all immune defects, while insulin treatment of streptozotocin-diabetic mice restored immune function to only 70-80% of normal levels. Results obtained by viability measurements and in vitro biological assays of lymphoid function, including proliferation in response to T- and B-cell mitogens, the production of interleukin-2 by T cells, and the production of interleukin-1 by macrophages indicated that direct exposure to alloxan for 48 h (at concentrations less than or equal to 14 mmol/l) had no adverse effects on lymphoid activity, while exposure to streptozotocin was routinely toxic at concentrations greater than or equal to 1 mmol/l. Both alloxan and streptozotocin exhibited strong toxicity in vitro for isolated pancreatic islet cells. Finally, lymphocytes from streptozotocin-diabetic mice, or cells incubated in vitro with streptozotocin, contained numerous chromosomal abnormalities indicative of DNA strand breakage. Such abnormalities were absent in alloxan-diabetic mice and in cells incubated with alloxan in vitro. These results indicate that immune dysfunction associated with streptozotocin is attributable to direct and irreversible impairment of lymphoid cell function and viability. In contrast, immune dysfunction associated with alloxan-diabetes appears to be a consequence of the diabetic state.(ABSTRACT TRUNCATED AT 250 WORDS)

Class I, II and III major histocompatibility complex gene polymorphisms in BB rats

The BB rat spontaneously develops insulin-dependent diabetes mellitus of autoimmune aetiology. From breeding studies, one of the genes necessary for the development of diabetes in these animals is linked to RT1, the rat's major histocompatibility complex. To study further the RT1 linked diabetogenic gene of the BB rat, we have studied restriction fragment length polymorphism using 32P-labelled DNA probes of the major histocompatibility complex genes. As we have previously reported, an I-A alpha probe (mouse class II gene) defines four chromosome types in the control BBN population, only one of which is found among diabetes prone BB rats. All BB rats we have studied are homozygous for the type IIa chromosome. Here we examine restriction fragment length polymorphisms using three other DNA probes. Using a DC beta-probe (human class II), the same pattern of polymorphisms (though different molecular weights) is found as with the I-A alpha probe. An H-2d C4 (fourth component of complement, mouse class III) defines no polymorphisms among or between BB and BBN rats. Using H-2 LdC-2 domain probe (mouse class I) many polymorphisms are apparent and in a limited series distinguishes I-A alpha defined IIa/IIa BBN rats from IIa/IIa BB rats. These studies provide the basis to subtype the RT1u identical BB and BBN animals and should aid in the localization and characterization of the RT1 linked diabetogenic gene of the BB rat.

Type I diabetes mellitus: a chronic autoimmune disease?

Currently defined categories of diabetes mellitus reflect our growing knowledge of the biochemical and immunologic basis of several disorders resulting in hyperglycemia. The authors discuss the autoimmune phenomenon and autoimmune diseases associated with Type I diabetes mellitus. Special focus is placed on the impact of immunologic assays on the current and future clinical care of patients with Type I diabetes and their genetically susceptible relatives.