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

In many developmental systems β -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 1–8 . 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 9 . 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, β -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 .