Type 1 diabetes is an autoimmune disease resulting from destruction of the insulin producing beta cells in the pancreas. The patients need life-long heavy treatment and still complications, both acute and later in life, are common. The incidence of type 1 diabetes has increased rapidly during the last decades, especially among young children. The disease can be predicted by genes predisposing type 1 diabetes, mainly human leukocyte antigen (HLA) genes, together with presence of autoantibodies to beta-cell antigens, where multiple autoantibodies confer the highest risk. A number of immune system intervention trials are now ongoing aiming to halt the progression of the inflammatory process in the beta cells.

This thesis aimed to investigate the prevalence and levels of autoantibodies in healthy children and in children with type 1 diabetes. Another aim was to study different properties of one of these autoantibodies, such as to which epitopes the antibodies bind and the distribution of immunoglobulin (Ig)-G subclasses, after immunomodulatory treatment in children with type 1 diabetes.

We found that positivity to autoantibodies against glutamic acid decarboxylase (GADA) and tyrosine phosphatase like protein islet antigen-2 (IA-2A) was associated with HLA risk genotypes in 5-year old children from the general population. HLA risk genotypes seemed important for persistence of autoantibodies and for development of type 1 diabetes, while emergence of autoantibodies, especially transient autoantibodies, seemed to be more influenced by environmental factors. Improved methods for detection of autoantibodies are needed, for prediction of diabetes and for identification of high-risk individuals suitable for prevention treatments. Therefore, an assay for measurement of insulin autoantibodies (IAA), based on surface plasmon resonance (SPR), was developed. The main advantages of this method are that there is no need for labelling and that it is time-saving compared to the traditionally used radioimmunoassay (RIA), but further development of the method is needed.

Treatment with GAD-alum (Diamyd) in children with type 1 diabetes has shown to preserve residual insulin secretion. This clinical effect was accompanied by an increase in GADA levels. We investigated the epitope reactivity of GADA in both GAD-alum and placebo treated children, and found that binding to one of the tested epitopes was temporarily increased after injection of GAD-alum. This result suggests that the quality of GADA was, to some extent, transiently affected by the treatment. On the other hand, no changes in binding to epitopes associated with stiff person syndrome (SPS) were observed, which together with the lack of change in GAD65 enzyme activity further strengthens the safety of the treatment. We also observed that the distribution of IgG subclasses was changed by GAD-alum treatment, with a lower proportion of IgG1 and higher IgG3 and IgG4. Lower IgG1 and higher IgG4 suggest a temporary switch towards a protective Th2 immune response, which has previously been observed in the same individuals for other immunological markers.

In conclusion, measurement of autoantibodies related to type 1 diabetes is an important tool for studying the autoimmune process in pre-diabetic and type 1 diabetic children. In addition to the use as markers of disease progression, the autoantibodies may be used for studying the effects of immunomodulatory treatments on the humoral immune response.