**Core Concept**
The thyroid gland uses a specific protein to transport iodine into the lumen of the follicles, where it is oxidized and attached to tyrosine residues on thyroglobulin. This process is crucial for the synthesis of thyroid hormones.

**Why the Correct Answer is Right**
Pendrin is a transmembrane protein that functions as a chloride-iodide transporter in the thyroid gland. It is responsible for the accumulation of iodide in the follicular lumen, where it is then oxidized and incorporated into thyroglobulin. This process enables the thyroid gland to concentrate iodide from the bloodstream, which is essential for thyroid hormone production. The pendrin protein is highly specific for iodide transport and is not involved in the transport of other ions or molecules.

**Why Each Wrong Option is Incorrect**
**Option A:** Endocytosis is a process by which cells internalize molecules or particles from the extracellular environment, but it is not the primary mechanism by which iodine is transported into the thyroid follicle lumen.

**Option C:** Antipo is not a recognized protein or mechanism involved in iodine transport in the thyroid gland. This option appears to be a distractor and is not a valid choice.

**Option D:** Primary active transport involves the use of ATP to transport molecules against their concentration gradient, but iodine transport in the thyroid gland is mediated by a secondary active transport mechanism involving pendrin.

**Clinical Pearl / High-Yield Fact**
Pendrin is also associated with congenital pendred syndrome, a condition characterized by sensorineural hearing loss, goiter, and thyroid hormone deficiency.

**✓ Correct Answer: B. Pendrin protein**