Which gland is primarily responsible for hormone secretion in the immune system?

The thymus gland plays a crucial role in the immune system by producing hormones that are essential for the development and maturation of T-lymphocytes, a type of white blood cell that is vital for adaptive immunity. These hormones, such as thymosin and thymopoietin, help regulate the immune response and promote the differentiation of precursor cells into functional T cells. The thymus is particularly active during childhood and adolescence, which is when the immune system is developing most robustly. As individuals age, the thymus gradually decreases in size and function, but its initial role in developing a competent immune system is foundational.

In contrast, the other glands listed have hormone functions that are primarily focused on different systems in the body. The pituitary gland, for instance, is known as the "master gland" because it controls various other endocrine glands but does not directly influence immune function. The adrenal glands produce hormones like cortisol and adrenaline that are involved in stress response and metabolism, while the thyroid gland regulates metabolism through hormones such as thyroxine. None of these glands primarily target hormone secretion linked to immune function like the thymus does.