Iodine use induces an increase of serum TgAb and TPOAb and a TgAb epitope spreading only in subjects with lymphocytic thyroiditis

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 432-458-Thyroid Autoimmunity
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-448
Francesco Latrofa*, Emilio Fiore, Teresa Rago, Lucia Antonangeli, Lucia Montanelli, Debora Ricci, Maria Annateresa Provenzale, Monica Frigeri, Maria Scutari, Fabrizio Aghini-Lombardi, Massimo Tonacchera and Paolo Vitti
University of Pisa, Italy
Iodine prophylaxis has been associated with a higher frequency of thyroid autoimmunity. We correlated thyroid autoimmunity and iodine use in 1295 subjects (502 M and 793 F), 45.7±19.2 yrs old, living in Pescopagano, an Italian village. 70.0% (906) of subjects declared to routinely use iodized salt (Iodized Salt Users: IS-Users) and 30.0% (389) to do not (IS-non Users). Urinary iodine excretion (UIE) was evaluated in 468 subjects. TgAb and TPOAb were measured in all subjects; high levels of TgAb and TPOAb were considered expression of clinical Hashimoto’s Thyroiditis (HT). According to thyroid ultrasound, the subjects were divided into two groups: HT pattern (HT-US) (n. 87, 6.7%) and non HT pattern (non HT-US) (n=1208, 93.3%). TgAb epitopes of 16 IS-Users and 17 IS-non Users HT patients were evaluated by inhibition of TgAb binding to Tg in ELISA using 4 human monoclonal TgAb-Fab.

Results. UIE was significantly higher in IS-Users (112.0, 65.0-166.0 µg/L) than in IS-non Users (86.5, 48.0-132.0) (p< 0.01). The frequency of positive TgAb was 18.9% (171/906) in IS-Users and 13.6% (53/389) in IS-Non Users (p = 0.02) and that of positive TPOAb was 16.9% (153/906) and 13.1% (51/389), respectively (p = 0.09). The percent of positive TgAb and TPOAb was higher in the HT-US than in the non HT-US group (p<0.01 for both). In the HT-US group the percent of positive TgAb was 58.5% (38/65) in IS-Users and 31.8% (7/22) in IS-non Users (p = 0.03), while that of positive TPOAb was 69.2% (45/65) and 45.5% (10/22), respectively (p = 0.05). In the HT-US group the percent of high levels of TgAb was 50.8% (33/65) in  IS-Users and 13.6% (3/22) in IS-non Users (p<0.01), while that of high levels of TPO was 61.5% (40/65) and 31.8% (7/22), respectively (p= 0.01). In the non HT-US group the percent of positive and high levels of both TgAb and TPOAb were similar in IS-Users and IS-non Users. The levels of inhibition by region B TgAb-Fab were 27.5% (6.5-48.3%) in IS-Users and 3.0% (0.0-20.5%) in IS-non Users (p=0.047); inhibitions by the other three TgAb-Fab were similar in IS-Users and Is-non Users.

In summary: i) serum thyroid autoantibodies are more common in IS-Users than in IS-non Users; ii) the effect of iodine is evident in subjects with HT-US and in patients with clinical HT; iii) iodine is associated with serum autoimmunity to Tg more than to TPO; iv) thyroid autoimmunity associated with the use of iodine is correlated with the expression of different TgAb epitopes. In conclusion, the use of iodine is associated with the onset of serum thyroid autoimmunity but this effect is observed only in subjects with a lymphocytic infiltration of the thyroid.

Nothing to Disclose: FL, EF, TR, LA, LM, DR, MAP, MF, MS, FA, MT, PV

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