Antibodies against thyroxine (T4) and/or triiodothyronine (T3) were detected in 3 patients with Hashimoto's thyroiditis. One of the patients had both anti-T4 and anti-T3 antibodies and the other 2 patients had only anti-T3 antibody.
Recovery of T4 or T3 added to the patients' sera determined by RIA was significantly low. The binding of 125IT4 or 125IT3 to the patients' sera was demonstrated by the polyethylene glycol method and by using RIA kits without adding the antibody provided.
The results in any unknown sample were compared to those obtained when an equal amount of standard serum was identically treated, and the results were expressed as unknown/standard ratios of bound 125I and bound 131I, respectively.
The binding activity was localized in the IgG fraction by column chromatography and by immunoprecipitation. T4- or T3-binding protein in two sera migrated in the gammaglobulin region on paper electrophoresis and was found in 7S fraction on Sephadex G-200 chromatography.
For one serum containing anti-T3 antibody and another containing anti-T4 antibody, the binding affinity and capacity were estimated by Scatchard plot analysis; affinity constants were 5.4 x 10(8) L/mol and 1.3 x 10(9) L-mol, respectively; capacities 1.4 ng/ml and 1.2 ng/ml, respectively.
The presence of anti-T3 and anti-T4 antibodies in serum may result in an apparent lowering of the serum T3 and T4 concentrations, respectively. PMID : 809458 PubMed - indexed for MEDLINE.
Thyroperoxidase (TPO) is an enzyme involved in thyroid hormone synthesis, catalyzing the oxidation of iodide on tyrosine residues in thyroglobulin for the synthesis of triiodothyronine and thyroxine (tetraiodothyronine). TPO is a membrane-associated hemoglycoprotein expressed only in thyrocytes and is one of the most important thyroid gland antigens.
These autoantibodies also frequently occur (6080) in the course of Graves disease. In patients with subclinical hypothyroidism, the presence of TPO antibodies is associated with an increased risk of developing overt hypothyroidism.
The initial step of the method therefore consisted in a dissociation of the postulated antigen-antibody complex by a 45 ammonium sulfate precipitation. The second part of the method consisted in incubating the euglobulins with trace amounts of 125I-T3 and 131I-T4.
Moderately increased levels of thyroperoxidase (TPO) antibodies may be found in patients with nonthyroid autoimmune disease such as pernicious anemia, type I diabetes, or other disorders that activate the immune system.
Serum T4 or T3 antibodies and the other 2 patients had only anti-T3 antibody. Serum T4 or T3 values measured by the single antibody radioimmunoassay (RIA were low or nil in these patients.
Many clinical endocrinologists use the TPO antibody test as a diagnostic tool in deciding whether to treat a patient with subclinical hypothyroidism, and Mayo Medical Laboratories endorses this practice. See Thyroid Function Ordering Algorithm in Special Instructions.
The hormones bound to the gammaglobulins were then separated from the free hormones by a column of DEAE Sephadex A-50 in ammonium acetate 0.05 M pH 7.6. The amounts of 125I and 131I bound to the gammaglobulin fraction were then measured.
Furthermore, it raises the concern that such patients may be at increased risk of developing other autoimmune diseases, such as adrenal insufficiency and type 1 diabetes. The frequency of detectable anti-TPO observed in nonimmune thyroid disease is similar to the 10 to 12 observed in a healthy population with normal thyroid function.