The immune system changes throughout life.
At birth, acquired (specific) immunity is not fully developed. However, newborns have some antibodies, which crossed the placenta from the mother during pregnancy. These antibodies protect newborns against infections until their own immune system fully develops. Breastfed newborns also receive antibodies from the mother in breast milk.
As people age, the immune system becomes less effective in the following ways:
These changes in immune function may contribute to the greater susceptibility of older people to some infections and cancers.
Last full review/revision October 2014 by Peter J. Delves, PhD