DOWN-SYNDROME (DS) PERIPHERAL-BLOOD CONTAINS PHENOTYPICALLY MATURE CD3+TCR-ALPHA,BETA+ CELLS BUT ABNORMAL PROPORTIONS OF TCR-ALPHA,BETA+, TCR-GAMMA,DELTA+, AND CD4+CD45RA+ CELLS - EVIDENCE FOR AN INEFFICIENT RELEASE OF MATURE T-CELLS BY THE DS THYMUS

Down syndrome (DS) thymocytes have a markedly diminished proportion of cells expressing high levels of the α,β T cell receptor (TCRα,β) and the associated CD3 molecule. Thus, we examined the surface expression of TCRα,β and CD3 as well as TCRγ,δ, CD4, CD8, Cd16, and CD45RA on peripheral blood lymphocytes (PBL) from 13 noninstitution-alized subjects with DS and 13 closely age-matched sibling controls using immunofluorescence and flow cytometry. DS PBL expressed high surface levels of TCRα,β and CD3, but, as compared to controls, they had a lower proportion of cells expressing TCRα,β (61% vs. 68%, respectively; P ≤ 0.05). Moreover, the absolute number of TCRα,β+ cells was considerably lower for DS subjects than for controls (1634 ± 229 vs. 2763 ± 530, respectively; P ≤ 0.05). DS subjects had a markedly higher proportion of cells expressing TCRγ,δ than did the controls (12% vs. 7%, respectively; P ≤ 0.02). In addition, DS subjects had a lower proportion of CD4+CD45RA+ cells than controls (22% vs. 35%, respectively; P ≤ 0.02), representing naive T cells which have recently emigrated from the thymus. The imbalance in the proportions of T cell subpopulations we have observed in DS PBL may contribute to the increased susceptibility to infection associated with DS and may represent a diminished efficiency in the production of newly differentiated T cells by the DS thymus. © 1992.