Abstract
Monosomy 21 (M21) is a rare aneuploid condition which in certain cases leads to reduced levels of chromosome 21 gene products. We have prepared an Epstein-Barr virus lymphoblastoid cell-line (LCL) from patient with M21 who has immunological abnormalities, and analysed the expression of lymphocyte function-associated antigen-1 (LFA-1). This heterodimeric leucocyte integrin consists of CD11a (alpha) subunits non-covalently associated with CD18 (beta) subunits coded, respectively, by genes on chromosomes 16 and 21. To determine whether monosomy 21 results in decreased expression of LFA-1, monoclonal antibodies were used to compare the expression of CD11a and CD18 on the M21 LCL with LCL from trisomy 21 (Down's syndrome, T21), normal controls and a possible case of leucocyte adhesion deficiency. In addition, phorbol-ester-induced homotypic adhesion, an LFA-1-mediated effect, was compared in these LCLs. The results are consistent with a gene dosage mediated reduction of LFA-1 expression by the M21 LCL.