EFFECTS OF ANTI-CD44 MONOCLONAL-ANTIBODY ON ADHESION OF ERYTHROID LEUKEMIC-CELLS (ELM-I-1) TO HEMATOPOIETIC SUPPORTIVE CELLS (MS-5) - CD44,BUT NOT HYALURONATE-MEDIATED, CELL-CELL ADHESION

Cocultivation of erythroid leukemic cells (ELM-I-1) with hemopoietic s upportive cells (MS-5) resulted in a specific adhesion of ELM-I-1 cell s to MS-5 cells. This phenomenon was designated as rosette formation. After induction of differentiation of ELM-I-1 cells, rosette formation was reduced, and no rosette formation was observed between erythrocyt es and MS-5 cells. Studies on anti-adhesion molecule antibody treatmen t have revealed that CD44 plays a key role in rosette formation. Expre ssion of CD44 on (the membrane of) ELM-I-1 cells was reduced after dif ferentiation, and no CD44 expression was detected on erythrocytes. CD4 4 was also expressed on MS-5. Hyaluronate is known as the ligand of CD 44, but neither hyaluronidase treatment nor addition of excess hyaluro nate to the assay system affected rosette formation. These data indica te that hyaluronate is not responsible for rosette formation. Anti-CD4 4 antibody (KM81), which recognized the hyaluronate binding site of CD 44, inhibited rosette formation. But other monoclonal antibodies again st different epitopes except for the hyaluronate binding site, even th ose against CD44's hyaluronate binding site, did not inhibit rosette f ormation. Thus, rosette formation between MS-5 cells and ELM-I-1 cells is mediated by CD44 but not by the hyaluronate binding site of CD44.