Erythroid developmental agglutinin is a protein lectin mediating specific cell-cell adhesion between differentiating rabbit erythroblasts.

In many developmental systems beta-galactoside-specific protein lectins have been identified as components which appear at the cell surface in concert with an initial requirement for cell-cell adhesion during tissue formation. Although some of these lectins have been purified, there has been little direct evidence concerning their role in establishing specific cell-cell contact. A mammalian system where selective cell-cell adhesion is evident and which is amenable to study is that of erythroid differentiation in the adult bone marrow. Here, the differentiation of erythroblasts takes place with the participants clustered together in the vicinity of a macrophage 'nurse' cell until the enucleation stage, when the immature reticulocyte is released and passes through the sinusoidal wall into the circulation. We show here that a small, beta-galactoside-specific, protein lectin can be extracted from erythroblast-enriched marrow and purified to homogeneity. This factor, termed erythroid developmental agglutinin (EDA), exhibits properties which strongly suggest that it is responsible for inter-erythroblast recognition and adhesion in vivo.