Monoclonal antibodies to CD18 and CD11A (LFA-1) distinguish Down's syndrome (trisomy 21) from normal lymphoblastoid cells.

To evaluate the potential of using fluorescence flow cytometry (FFC) in the diagnosis of Down's syndrome we analysed a series of Trisomy 21 lymphoid cell-lines (LCL) with a panel of monoclonal antibodies (MoAb) to the CD11a and CD18 subunits of lymphocyte function associated antigen 1 (LFA-1). In pairwise analysis of Trisomy 21 (T21) and normal LCL with 6 CD18 and 10 CD11a MoAb we found that T21 LCL could be distinguished from normal LCL with both types of MoAb, even though only the CD18 gene is duplicated in Down's syndrome. Experiments in which CD18 or CD11a were capped showed that the two subunits co-migrate on T21 and normal LCL, probably as heterodimers. This appears to explain the increased expression of CD11a on Trisomy 21 LCL. There was no evidence that T21 LCL express the other two leucocyte integrin subunits CD11b and CD11c, indicating that Trisomy 21 has little affect on tissue specific control of these molecules. In contrast, there appears to be reduced expression of an unrelated adhesion molecule LFA-3 on Trisomy 21 LCL. We discuss the relevance of these results in the diagnosis of Down's syndrome.