Between the breastbone and the heart is the thymus. It has a more specialized function with regard to our body’s immune system. It is the thymus that helps the T cells develop and enables them to function as protectors of the body. This is accomplished through the genetic rearrangement of the receptors in the T cell during its maturation phase in the thymus. It is especially important in newborn babies – without a thymus a baby’s immune system collapses and the baby can die

The thymus reaches its maximum potential during the childhood years of a person into puberty, eventually undergoing atrophy in middle to old age. This is because a large majority of the total stock of T cells are already produced and accumulated in the early years of life, so the thymus is less and less used as the years go on. In adults it can be removed without a problem because the other parts of the immune system can handle the job.