Erythropoiesis: comparison of in vivo and in vitro amplification.

1. Amplification is defined as the phase of erythropoiesis that includes all cell divisions of the recognizable erythron. 2. In vivo, amplification always takes place surrounding a central histiocyte (erythroblastic island). It is made up of four to five successive synchronous divisions. 3. In vitro, complete maturation and amplification of erythropoietic cells can be obtained without apparent association with a central histiocyte. 4. The functional significance of the 'erythroblastic island' and disorders of amplification are discussed in relation to clinical disorders of erythropoiesis.