The expression of LFA-1 is increased on down's syndrome (Trisomy 21) Platelets

Abstract We have previously demonstrated the presence of lymphocyte function associated antigen-1 (LFA-1) on human platelets. The genes encoding the CD18 (LFA-1 β chain) and CD11a (LFA-1 α chain) are located on chromosomes 21 and 16 respectively. Down syndrome patients are known to have a substantial overexpression of LFA-1 on lymphoid cells, probably due to the extra copy of CD18 gene in Trisomy 21 (T21). However, on some cells (monocytic and granulocytic), the effect of T21 was not clear. In this study, we looked for a possible difference in LFA-1 expression between T21 and normal donor platelets, using comparative flow cytometry analysis and Western blot. Using this approach, we show that the expression of the common β subunit LFA-1 was constitutively increased on platelets from 5 to 7 T21 patients. The expression of the α chain on resting and thrombin-activated platelets from children or adults with T21 compared to age-matched controls, showed a similarly increased expression to that of the β chain. These data indicate that a trisomy-dependent constitutive effect on the expression of CD18 on platelets occurs in Down's syndrome, and that this also increases CD11a expression, which therefore leads to the overexpression of LFA-1. This alteration may be related to the higher incidence of cardiovascular disease in such patients.