Lymphocyte subpopulations in Down's syndrome: High percentage of circulating HNK-1⁺, Leu 2a⁺ cells

Peripheral blood lymphomononuclear cells (PBL) from 35 patients with Down's syndrome (DS, trisomy-21; 25 institutionalized and 10 non-institutionalized) were phenotypically characterized by means of various monoclonal antibodies. They included a high percentage of T lymphocytes with low avidity for sheep erythrocytes as well as an extremely high percentage of HNK-1⁺ cells and of lymphocytes reacting with the OKT8 and Leu 2a antibodies. The HNK-1⁺ cells of DS include four different subsets: (a) E⁺, OKT3⁺, OKT8^-, Leu 2a^-; (b) E⁺, OKT3⁺, OKT8⁺, Leu 2a⁺; (c) E^-, OKT3^-, OKT8^-, Leu 2a^- and (d) E^-, OKT3^-, OKT8⁺, Leu 2a⁺. Subsets (a) and (c) are also present in PBL from karyotypically normal controls while subsets (b) and (d) have a phenotype which has not been previously reported. These findings may be related to the triple expression by trisomic cells of the receptor for interferon, which is coded by a gene located on chromosome number 21. Alternatively, the high number of 'immature' NK cells of DS, possibly identical with pre-T lymphocytes, may originate from the congenital thymic derangement associated with trisomy 21.