Downregulation of CD43 in RAEB and RAEB-T patients. Report of 3 cases.

CD43 (leukosialin, sialophorin) is a cell surface mucin expressed at high levels on most leukocytes and is reported to be involved in adhesion, anti-adhesion, and signal transduction prodders. Regulation of its expression is thought to take place through methylation of the DNA in the nonproducing cells, and the methylation inhibitor 5-azacytidine induces expression of the sialophorin gene. Here we report three cases of patients with myelodysplastic syndromes in which acquired severe deficiency of the CD43 antigen on the surface of most hemopoietic cells was observed. Peripheral blood mononuclear (PBMC) cells from 32 MDS patients and 20 healthy individuals were analyzed by flow cytometry after labeling with an anti-CD43 (DF-T1) monoclonal antibody. In 1 patient with refractory anemia with excess of blasts (RAEB) and 2 patients with refractory anemia with excess of blasts in transformation (RAEB-t), the percentages of CD43(+) PBMC were 3.8%, 6%, and 9.9%, respectively. The deficiency was observed at protein and RNA level as confirmed by western and southern blot, while analysis of the DNA by single-strand conformation polymorphism and sequencing did not reveal any difference in the gene sequence between the CD43(+) and CD43(-) cells of these patients. It is known that patients with MDS may have normal and dysplastic population of hemopoietic cells. Further studies are needed to reveal the mechanism of downregulation of the gene in these 3 patients and whether the phenomenon is related to the dysplastic population only or not.