IDR/A and IDR/B-specific anti TPO aAbs mainly recognize the same regions on hTPO: the binding strength makes the difference. IDR/A- and IDR/B- specific epitopes (left and right panel respectively) are globally composed by the same peptidic regions on hTPO. Region 599–617 (in orange) represents the amino acid sequence predominantly recognized by IDR/A-specific anti-TPO aAbs (as illustrated by three yellow lines on the left panel). On the hand, IDR/B-specific anti-TPO aAbs bind several regions widely spread on the IDR. The immunodominant binding surface (in blue) and region 599–617, composed the IDR/B-specific epitopes as shown by the yellow lines which illustrate the contact points on hTPO. As not shown in the figure, the CCP-like domain may contribute to the immunodominant epitopes.