The thymus is located just below the breast bone. It is relatively large in infants and grows until puberty. In adulthood, it starts to slowly shrink and become replaced by fat, according to the National Institute of Neurological Disorders and Stroke. It can weigh only 5 grams in elderly adults.

What does the thymus do in adults?

The thymus is responsible for producing and maturing lymphocytes, or immune cells. These include T cells, a type of white blood cell that defends the body from infections. Additionally, the thymus suppresses the effects of aging, according to a 2016 study.

Is thymus absent in adults?

Hypothetically, the thymus should stop functioning at around 105 years of age; but, studies with bone marrow transplant patients have shown that the thymi of the majority of patients over forty were unable to build a naïve T cell compartment.