Down's syndrome: problems of immunodeficiency.

The high susceptibility to infections, malignancies, and autoimmune disorders of subjects with Down's syndrome (DS) is associated with laboratory and pathological evidence of immunodeficiency. The percentage of circulating T-lymphocytes is indeed low from birth, and lymphocyte proliferative response to mitogens, normal during the 1st decade of life, declines rapidly thereafter. There is indirect evidence that T-lymphocyte maturation is impaired in DS; furthermore, the thymus is morphologically deranged and there is recent direct evidence that serum levels of thymic hormones are low. It is suggested that the immunodeficiency of DS results from a defect limited primarily to the epithelial cells of the thymus which fail to synthesize or secrete one or more hormones necessary for the differentiation of T-lymphocytes.