The primary function of the thymus in immune response is to facilitate the maturation of T cells, a crucial component of the adaptive immune system. Located behind the sternum, the thymus serves as the site where precursor cells differentiate into functional T cells. This process is vital for the immune system to recognize and respond effectively to pathogens. Through a process called positive selection and negative selection, the thymus also ensures that T cells can distinguish between self and non-self, thus preventing autoimmune diseases.