The erythroblastic island: past and future.

The erythroblastic island consists of a macrophage surrounded by erythroblasts of different maturation stages. The cohesion of cells is lost during spreading, so that the islands can no longer be seen in smears. However, in undisturbed preparations, either living or fixed, the islands can be visualized, isolated, cultured, and their function studied. Many questions remain, such as the production of growth factors by the macrophage, the causation of the adhesion of cells forming the islands, the role of calcium in the adhesion, and others. New technical advances, including flow cytometry, immunolabeling, and in situ hybridization will assist in answering these questions.