Insulin autoantibodies in patients with autoimmune diseases.
Insulin antibodies (IAA) can be detected in the serum of the majority of newly diagnosed IDDM patients prior to insulin therapy. In first degree relatives of IDDM patients, IAA are associated with an increased risk of development of IDDM. However, the disease specificity of IAA, detected by radiobinding assays, has not been addressed. We thus tested sera from patients with autoimmune disease for IAA. One of 29 (3%) patients with Graves' disease and five of 27 (19%) patients with SLE had IAA levels exceeding the range for normal controls. IAA were not detected in sera from 29 patients with Addison's disease, 15 patients with pernicious anaemia or 10 patients with increased gamma globulins. Non-specific binding of 125I-labelled insulin was increased in serum from 14 (21%) samples from patients with Graves' disease, 10 (37%) patients with SLE, one (3.2%) of 29 patients with Addison's disease and two (13%) of 15 patients with pernicious anaemia. The increased non-specific binding most likely relates to immunoglobulin binding as it was also found in eight of 10 patients with oligoclonal or polyclonal increase in gamma globulins. Our findings suggest that moderate elevations of IAA are not uncommon in patients with SLE, in whom increased non-specific binding of insulin is also common. This observation is of importance in preclinical diabetes screening studies.