HLA-DR3 and HLA-DR5 confer risk for autoantibody positivity against the thyroperoxidase (mic-TPO) antigen in healthy blood donors.

The prevalence of circulating autoantibodies against thyroperoxidase (mic-TPO) was determined in 3,000 healthy blood donors (age range: 23 to 60 years) from the Hamburg area. Of the blood donors, 153 (5.1%) were found to have high titer of mic-TPO (> 350 IU/ml). Only two autoantibody positive subjects (0.06%) were chemically hyper- and hypothyroid, respectively. Analysis of HLA-DR specificities revealed that HLA-DR specificities DR3 and DR5 were significantly increased when compared to controls (n = 1,863). Comparison of the autoantibody-positive probands with a group of disease controls, i.e., Graves' patients and patients with lymphocytic thyroiditis, revealed a higher prevalence of HLA-DR3-positive HLA haplotypes in the disease controls when compared to autoantibody positives. Individuals with a mic-TPO level greater than 2,000 IU/ml were almost exclusively found to have one HLA-DR3 or HLA-DR5 positive HLA haplotype. We conclude that a high prevalence of high-titer mic-TPO can be found in healthy blood donors. Circulating signs of thyroid autoimmunity were associated with HLA specificities also found to be associated with autoimmune thyroid diseases.