Evidence that the Fc receptor is distinct from the specific associated antigen of K-562 cells

Studies of the K-562 cell line demonstrate convincing evidence these these cells can spontaneously or inducibly differentiate into erythroid (5, 22, 27, 28, 60, 80,), megakaryocytic (33, 60, 97), monocytic (50, 60), ganulocytic (44, 60, 65, 66, 85) and lymphoid (52, 60, 78) progenitor cells. In addition to being a pluripotent stem cell, the K-562 cell is very sensitive to NK cell lysis, can bind aggregated IgG or hemolysin coated sheep erythrocytes (EA) via its Fc receptor (FcR), and will lyse in an ADCMC reaction with antisera prepared in rabbits, monkeys, or goats. Furthermore, anti-K-562 gamma globulin absorbed with normal peripheral blood leukocytes and bone marrow cells still mediates ADCMC and will inhibit EA rosette formation (45). The fact that this antibody preparation showed two distinct immunological activities but was considered to be against a unique leukemia-associated antigen of K-562 led to the postulation that the ADCMC antigen and the FcR were the same or intimately close together on the cell surface. Thus, one antibody species would either cause ADCM3 or interfere with rosette formation.

The FcR is likely to be antigenically different from the FcR on the normal cells used to absorb the antiserum. Since most studies suggest the inability of K-562 cells to switch from precursor to mature status (or from fetal to adult as in the erythroid hemoglobin marker studies on K-562 cells), it is possible that the FcR on K-562 cells is of a fetal variety and antigenically distinct. Although Ichiki et al. (45) provided indirect evidence that the ADCMC antigen and the FcR on the K-562 cell were the same or closely associated molecules, in the present study, a more defnitive approach was used to test this hypothesis.