T lymphocytes in patients with Down's syndrome.

: Individuals with Down's syndrome (DS) are thought to have abnormalities in their immune system, and a tendency to infection and malignancy. Studies to quantify the number of T lymphocytes in the peripheral blood of 82 unselected institutionalized patients (50 DS, 27 controls matched for sex and age, 2 chronic lymphocytic leukemic, 2 acute leukemic, and 1 Hodgkin's disease) were conducted. The numbers of circulating T cells in DS patients did not differ significantly from the control group, and were in the upper limits of normality. Number of "avid" T cells, however, were significantly higher in the DS than in the control group. The blastogenic response of the T cells to mitogen was significantly depressed. The data did not exclude the existence of qualitative abnormalities. Except for DS patients with congenital heart disease, those older than 15 years were not more prone to upper respiratory infections than other institutionalized mentally retarded patients.