Autoimmunity and diabetes
Immunological dogma once maintained that the body could not lodge an immune attack upon its own tissues. This belief was eroded by the discovery of autoantibodies in the 1950s, which led on to the identification of organ-specific autoimmune diseases such as Hashimoto's thyroiditis and autoimmune Addison's disease. Conditions such as these involve activation of both humoral and cellular immune mechanisms, overlap with one another, and have associations with the HLA system, suggesting a basis for immunological specificity. Recognition that type 1 diabetes belongs to this group of diseases was delayed by a failure to distinguish between type 1 and type 2 diabetes, and difficulties in demonstrating autoantibodies directed against the pancreatic islets. This page traces the rise of the autoimmune paradigm, and explains why it took another 20 years for the immune basis of type 1 diabetes to be recognised.
Paul EhrlichPaul Ehrlich commented in 1900 that the organism 'possesses certain contrivances, by means of which the immunity reaction, so easily produced by all kinds of cells, is prevented from acting against the organism’s own elements and so giving rise to autotoxins ... so that one might be justified in speaking of a horror autotoxicus'. This soon became the ruling dogma, although he also said that 'when the internal regulating contrivances are no longer intact ... great dangers arise. In the explanation of many disease-phenomena, it will in the future be necessary to consider the possible failure of the internal (i.e. immune) regulation.'
In 1957 Witebsky and Rose demonstrated that isoantibodies (antibodies against tissues from the same species) could be generated by crude extracts of thyroid or purified thyroglobulin, a protein specific to the thyroid. They went on to show that animals could also develop autoantibodies against their own thyroid when extracts were reinjected together with adjuvant. A surgical collaborator pointed out that the associated changes in the thyroid resembled Hashimoto’s thyroiditis, prompting them to search for and detect thyroid autoantibodies in affected patients. They were however beaten to publication by Roitt and Doniach, who proposed that 'destruction of the thyroid in Hashimoto’s disease results from progressive interaction of thyroglobulin in the gland with the autoantibody present in the patient’s circulation'. Adrenal autoantibodies were soon found in idiopathic Addison’s disease, in which lymphocytic infiltration of the thyroid is an associated feature, suggesting an autoimmune basis for both conditions.
Rosalyn YalowFurther evidence of autoimmunity came from the demonstration by Berson and Yalow of insulin-binding globulin in the serum of insulin-treated diabetic patients, a discovery that opened the way to the radioimmunoassay of insulin. The concept that insulin could itself elicit an immune response immediately suggested that this response could in some way contribute to the development of diabetes.
The paradigm shift was abrupt. Macfarlane Burnet informed the staff at the Walter and Eliza Hall Institute in 1957 that the Institute was switching from virology to immunology. The implication was clear: get into immunology or get out. Other clinical disorders were rapidly fitted to the autoimmune model, and the central features of the paradigm were essentially in place by 1963.
Autoantibodies were commonly detected in the 1960s by indirect immunofluorescence, a two-step technique. In step one, the serum to be tested is washed over a frozen section of the target tissue so that any antibodies present in the serum will bind to that tissue. In the second step, the tissue section is exposed to antibodies to human immunoglobulin labelled with fluorescein isocyanate. The antibody to be tested is thus sandwiched between the tissue antigen and the labeled anti-immunoglobulin antibody, and the antigen-antibody complexes will fluoresce under the microscope at the appropriate wavelength of light. This method was later used to detect islet cell antibodies (ICAs), but only after many unsuccessful attempts to do so. The reasons for this will become apparent.
Overlap with other autoimmune disease
As noted above, autoimmune thyroid and adrenal disease are associated conditions. Further overlap has been described with pernicious anaemia and a other conditions including coeliac disease and rheumatoid arthritis, whereas there is a negative association with multiple sclerosis, mediated by its association with HLA-DR2, which confers protection against diabetes. Organ-specific autoimmunity was noted to be more common in juvenile (type 1), but not in maturity-onset (type 2) diabetes, but this understanding was delayed by a failure to appreciate that these represent quite different disease processes.
Organ-specific cellular immunity
Jorn NerupSophisticated methods are needed to demonstrate activation of organ-specific cellular immunity, and such techniques were lacking in the early days of the autoimmune paradigm. Unusually, abnormal cellular immunity was identified before autoantibodies in type 1 diabetes. This arose because Nerup, who had previously demonstrated cell-mediated immunity in autoimmune Addison's disease, now went on to examine this in juvenile diabetes using the now obsolete introduced leucocyte migration test, which could identify the presence of T cells primed against the antigen tested. These mechanisms were of course unknown at the time, but the test was recognised as a measure of 'cellular hypersensitivity'. Nerup speculated that cellular hypersensitivity was the counterpart of the infiltration seen in insulitis, and that cell-mediated immunity could therefore play an important part in the pathogenesis of insulin-dependent diabetes.
The discovery of the HLA system
Human leucocyte antigens (HLA) were first identified as the human equivalent of transplantation antigens recognised in the mouse. Mouse studies showed that these antigens controlled immune responses to viruses and other antigens, and associations with a range of human disorders were soon reported, beginning with Hodgkin's disease in 1967. Autoimmune disorders were prominent among the HLA-associated disorders. The HLA Class 1 associations of juvenile diabetes were reported by Nerup and colleagues in 1974, and very soon after by Cudworth and Woodrow.
The discovery of islet cell antibodies (ICA)
The long delay in acceptance of the idea of autoimunity in diabetes was mainly due to two factors: failure to make a clinical distinction between the two major types of diabetes; and failure to detect antibodies directed against the pancreatic islets. Indirect immunofluorescence was the technique of choice in this attempt, and many investigators had tried to find these unsuccessfully before they were first demonstrated by Bottazzo and Doniach in 1974. In retrospect, there were many reasons for this:
- ICA can be detected in 70–85% of recently diagnosed individuals but fade over time; they do not show up well in longer duration patients.
- The fluorescence response is relatively weak, and is best demonstrated with microscopes that provide epi-illumination. Such microscopes had not been available to earlier investigators.
- ICA are more readily detected in fresh blood group O pancreas than in pancreases from donors with other blood groups.
Franco Bottazzo These elements came together, not without a certain degree of serendipity, when Franco Bottazzo prepared his thesis on Addison's disease under the supervision of Deborah Doniach. He set out to screen a panel of other tissues, including the pancreas, and had access to the right quality microscope, to fresh group O pancreas (provided by his co-worker Richard Lendrum), and above all to a freezer full of serum from patients with multiple endocrine autoimmunity. Such patients often have high persistent levels of GAD antibodies, one of the components of the ICA staining reaction, and his pancreas sections therefore lit up under the microscope.
This finding was replicated almost immediately by McCuish and colleagues in Scotland, and so it was that two of the key missing elements needed to fit juvenile (type 1) diabetes into the autoimmune paradigm were published in the Lancet within a few weeks of one another.
Further confirmation of the autoimmune (or, as some prefer, immune-mediated) basis of type 1 diabetes appeared in subsequent years. This included, among other elements, the introduction of the non-obese diabetic (NOD) mouse, cellular transfer of diabetes in rodents and – accidentally – in humans, and the observation that immunosuppression could influence the course of newly-diagnosed diabetes. Nonetheless, a true paradigm shift in our understanding of type 1 diabetes occurred within the space of a few months in 1974.
^ Ehrlich P, Morgenroth J. On haemolysins. Fifth communication. F. Himmelweit, ed. In: The Collected Papers of Paul Erlich, vol. 2. Pergamon, London, 1957, pp. 246–55
^ Rose NR. Studies of thyroid their role in shaping modern immunology. Gallagher RB, Gilder J, Nossal GJV, Salvatore G, eds. In: The Making of a Modern Science. London, Academic, 1995
^ Roitt IM, Doniach D, Campbell PN, Hudson RV. Auto-antibodies in Hashimoto’s disease (lymphadenoid goitre). Lancet 1956;271(6947):820–21
^ Burnet FM. The new approach to immunology. New Engl J Med 1961;264:24–34
^ Gale EAM. The discovery of type 1 diabetes. Diabetes 2001;50:217–26
^ Nerup J, Andersen OO, Bendixen, G et al. Cell-mediated autoimmunity in diabetes mellitus. Proc R Soc Med 1974;67:506–13
^ Nerup J Platz P, Andersen OO et al. HL-A antigens and diabetes mellitus. Lancet 1974;2:864–6
^ Bottazzo GF, Florin-Christensen A, Doniach D. Islet-cell antibodies in diabetes mellitus with autoimmune polyendocrine deficiencies. Lancet 1984;2(7892):1280–3