Down's syndrome lymphoid cell lines exhibit increased adhesion due to the over-expression of lymphocyte function-associated antigen (LFA-1).

We have analysed homotypic adhesion induced by the phorbol ester TPA in EBV-immortalized Down's syndrome (trisomy 21) and normal lymphoblastoid cell lines. Our results show that the trisomy 21 cells aggregated more readily than normal cells. The aggregation of the two types of cell was blocked effectively by the addition of monoclonal antibodies to the alpha and beta chains (CD11a, CD18) of lymphocyte function-associated antigen (LFA-), but not by monoclonal antibodies to LFA-3 and the alpha chain of p150,95 (CD11c). Since TPA did not increase the expression of CD18 on trisomy 21 cells, we conclude that the increased adhesiveness is the result of over-expression of CD18 as a result of gene dosage.