Normal development of the immune response is due in part to hormones produced by the .

thymus gland

Explanation:

The thymus gland is  located behind your sternum and between your lungs, is only active until puberty.

After puberty, the thymus starts to slowly shrink and become replaced by fat.

Thymosin is the hormone of the thymus, and it stimulates the development of disease-fighting T cells.

Thymus gland

Explanation:

Thymus gland are vital organ that are small in size and they can be found behind the breastbone. Thymus can start to decay during puberty and they help to fight infection due to the presence of T cells which is an important white blood cells in the body and they are most active during puberty, but reduce in size after puberty due to the fact that they are replaced by fat.

Thymus enables vital organs in the immune system to grow properly and it involved development of the immune system in adolescent.

Therefore Normal development of the immune response is due in part to hormones produced by the THYMUS GLAND