The study of the immunopathogenesis of IDDM in patients is hampered by several restrictions:
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The onset of IDDM is relatively late in the natural history of the immune process since almost 80-90% of islets have to be destroyed before insulin deficiency is diagnosed.
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The site of the immune process, the islet of the human pancreas, is not easily accessible for investigations.
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The disease process in humans is quite heterogenous. Therefore, animal models of Type 1 diabetes are necessary for the study of human disease.
Are animal models sufficient to describe the pathogenesis in human patients? I think the answer is clearly no! Animal models of Type 1 diabetes differ from human IDDM, e.g. by the genetic homogeneity of inbred animals or sex bias and environmental triggers. Moreover, the commonly used animal models such as the NOD mice or BB rats have very special genetic defects, e.g. the I-A deletion in NOD mice or the lymphopenia in BB rat. These defects may induce further diseases such as thyroiditis and sialitis that are not commonly observed in human IDDM. Altogether, there is no possibility of rejecting animal models in the study of IDDM. The results should be considered with great care before applying to human disease especially if new concepts for therapy are concerned. Then, animal models of Type 1 diabetes are relevant for IDDM in humans as long as the limitations of this approach stay in mind.