Expression of the CD15 antigen on normal and leukemic myeloid cells: effects of neuraminidase and variable detection with a panel of monoclonal antibodies.

Normal and malignant myeloids cells are known to express cell surface molecules having in common the carbohydrate antigen lacto-N-fucopentaose-III (LNF-III--termed CD15). We used flow cytometry to examine the variability of CD15 expression in normal cells and acute myeloid leukemia (AML) cells as detected by 24 murine monoclonal antibodies (mAb). Important differences in the levels of binding were observed with the various mAb. Titrations of each mAb were performed to confirm that these differences in binding were due to increased antigen detection and not differences in concn. In studies of CD15 expression on AML cells selected from a large prospective study, anti-CD15-1 (also known as PM-81) showed the highest binding to each case. Neuraminidase was added to cells from seven AML patients that we had previously found to be low in CD15 expression, in order to determine if cryptic CD15 was present on these cells. Neuraminidase enhanced binding of each of the entire panel of mAb on five patients' cells, thus demonstrating the ubiquitous expression of CD15 on AML cells. In two cases, binding of only some of the mAb was increased, indicating exposure of unusual epitopes on those cells. Subpopulations of normal peripheral blood lymphocytes, cells not associated with CD15 expression, also substantially increased their level of binding to some of the mAb after the addition of neuraminidase. Two-color flow cytometry was used to determine the immunologic phenotype of the lymphocytic population that expressed CD15. This technique revealed that 9.5% normal lymphocytes coexpressed the CD15 and CD3 (T cell) antigens. In addition, by gating on large granular lymphocytes we found that 24.4% of these cells coexpressed CD15 (detected by PM-81) and CD2 (sheep erythrocyte receptor), while 50.3% expressed CD15 and CD16 (type III Fc receptor, natural killer cell-associated). This is consistent with the notion that sialylated CD15 is expressed on some natural killer cells and T cells.