Antibodies against Proinsulin and Homologous MAP Epitopes Are Detectable in Hashimoto's Thyroiditis Sardinian Patients, an Additional Link of Association

Abstract

Hashimoto's thyroiditis (HT) is the prevailing organ-specific autoimmune disease in Sardinia, often complicated with other autoimmune disorders, most commonly type 1 diabetes (T1D). While numerous studies describe levels of anty-thyroid antibodies (Abs) in T1D patients, few papers evaluate the status of anti-islet autoimmunity in subjects affected by HT. Previously, we portrayed Mycobacterium avium subspecies paratuberculosis (MAP) as an environmental factor strongly associated with both diseases. In this study, we analyzed plasma of Sardinian HT patients (n=177) and healthy controls (HCs; n=175) for the presence of Abs against proinsulin and MAP-derived homologous epitopes: MAP1,4αgbp157-173/PI64-80 were recognized by 5,08% and 18,64% of HT vs 0,57% and 7,43% of HCs (AUC=0,6 for both; p<0,0003 and 0,002, respectively), whereas the prevalence of Abs against MAP2404c70-85/PI46-61 peptides was higher but not significant in patients when compared to HCs. In women (n=152), Abs against MAP1,4αgbp157-173 were detected in 12,50% of HT vs 2,75% of HCs (AUC=0,63; p<0,0002), while positivity to its human homolog PI64-80 was observed in 16,42% of HT vs 6,42% of HCs (AUC=0,61; p<0,001). In men (n=25), a significant anti-PI46-61 Abs levels were detected in 4% of HT vs none of the HCs (AUC=0,7; p<0,003). Age-related analyses revealed the highest prevalence between 31-40 years old (45,83%) in the total study population and among males (33,33%); in contrast, women had a higher seroreactivity between 51-60 years (42,11%). A further follow-up and determination of anti-islet Abs levels is needed to evaluate the association of immune responses directed against the MAP/PI homologous peptides with progression to overt diabetes in HT subjects.

Fig 1. Prevalence of serum Ab positivity to MAP1,4αgbp_157-173/PI_64-80 and MAP2404c_70-85/PI_46-61 homologus epitopes in Sardinian HT patients and age/sex-matched HCs.

Fig 2. Sex-related prevalence of Abs against MAP1,4αgbp_157-173/PI_64-80 and PI_46-61 in Sardinian HT patients and HCs.

Plasma was tested for immunoreactivity against plate-coated homologous peptides MAP1,4αgbp_157-173/PI_64-80 and MAP2404c_70-85/PI_46-61. Statistical analyses were performed for all peptides separately in the context of entire study population (A, B), female (C, D) and male (E) HT subjects and HCs. The dotted lines indicate thresholds of positivity relative to each assay calculated by ROC analysis. The percentage of Abs-positive patients is reported on top of each distribution; horizontal bars correspond to means. AUC and p values (CI 95%) are indicated in the top right corner. Only statistically significant data are reported.