Possible participation of colloid antigen 2 and abhormone (IgG with hormone activity) for the etiology of Graves' disease.

The theory that antibody (Ab) directed against the TSH receptor (TSHR) (TSHRAb) is the causal factor of Graves' disease seems unlikely. Corticosteroids have not had a curative effect on the hyperthyroidism of Graves' disease despite their effectiveness for other autoimmune diseases. Two kinds of TSHRAb, thyroid-stimulating Ab (TSAb) and thyroid-blocking Ab (TBAb), are known as causal factors of hyperthyroidism and hypothyroidism, respectively. Previously, we reported that TSAb may be thyroid stimulating animal IgG-like hormone and TBAb may be the precursor of TSAb. In this paper we suggested that TBAb (precursor) converts to TSAb (active form) via the action of the protease, colloid antigen 2 (CA2). We speculate that the conversion of TBAb to TSAb is controlled by two factors: the protease and an anti-protease Ab. When anti-protease Ab levels are high, the patient exhibits hypothyroidism due to the increase in TBAb levels caused by neutralization of the protease. When anti-protease Ab levels are negative, the patient's hypothyroidism disappeared by the negative serum TBAb due to increased protease. An immunoglobulin G (IgG) with enzyme activity is known as an abzyme, which may be an undeveloped form. IgG with hormone activity may be likewise called an abhormone, which could also be an undeveloped form. The tumor marker CEA is a known member of the IgG supergene family. Many ancestral versions of proteins may have been produced as an IgG form. Possible participation of colloid antigen 2 and abhormone for the etiology of Graves' disease is suggested.