THE ADHESION MOLECULE E-CADHERIN AND A SURFACE-ANTIGEN RECOGNIZED BY THE ANTIBODY 9C4 ARE SELECTIVELY EXPRESSED ON ERYTHROID-CELLS OF DEFINED MATURATIONAL STAGES

The antigen expression of immature erythroid bone marrow cells was stu died using two recently generated monoclonal antibodies (mAb), mAb 67A 4 and 9C4, with specificities for the epithelial cell adhesion molecul e E-cadherin (E-Cad; mAb 67A4), and a novel 110 KDa differentiation an tigen (mAb 9C4) with unknown molecular structure. Pappenheim staining of FAGS-purified cells labeled with mAb 9C4 and anti-glycophorin A (GA ) revealed that the majority of the 9C4+GA- and 9C4+GA+ cells consiste d of erythroblasts. In contrast, the E-Cad-positive population compris ed normoblasts and erythroblasts. While the E-Cad+GA- fraction contain ed mainly erythroblasts and basophilic normoblasts, the E-Cad+GA+ popu lation was enriched in orthochromatic and polychromatophilic normoblas ts. By colony assays of affinity column-purified cells it could be sho wn that erythroid colony forming units (CFU-E) were enriched and eryth roid burst forming units (BFU-E) were depleted in the 9C4- and E-Cad-p ositive fractions. Flow cytometric analysis of bone marrow cells doubl e-labeled with mAb 67A4 and anti-CD71, anti-CD117, anti-CD34, or anti- GA revealed that about 90% of the E-Cad-positive cells coexpressed CD7 1, about 70% were positive for CD117, about 50% for GA, and only about 5% coexpressed CD34. The expression pattern of 9C4 antigen was simila r to that of E-Cad with the exception that only a minority of the 9C4- positive cells coexpressed GA. Lymphoid and myeloid markers were negat ive on both the E-Cad- and 9C4-positive populations. In these studies we describe the identification of a new mAb-defined antigen which is s pecifically expressed on erythroblasts and CFU-E (9C4) and demonstrate that E-Cad is not only expressed on epithelial cells but also on eryt hropoietic cells of defined maturational stages.