Based on simple microscopic cell morphology in blood and bone marrow smear preparations, it seems to be likely that the cell differentiation and terminal differentiation in human blood cells, and particularly in erythroid or granulocytic lineages, simultaneously reflect ageing of the lineage progenitors and terminal differentiation steps. The terminal differentiation stages of both these lineages actually appear as senescent cells. Abnormal ageing of progenitor cells may represent one of the "dysplastic" phenomena of the premature terminal differentiation state. Such state is characterized by heterochromatin condensation and nucleolar morphology similar to that in fully differentiated terminal cells of granulocytic or erythroid lineages. It should also be mentioned that in some known erythropoietic disorders, less differentiated erythroblasts may lose nuclei similarly as "normal" fully terminally differentiated cells of the erythroid cell lineage. It seems to be clear that cells in both abnormal less differentiated and terminally differentiated stages of erythroid or granulocytic lineages lose the ability to multiply similarly as senescent cells. On the other hand, the background of cell ageing and differentiation is very complicated and requires a different approach than the simple microscopic morphology at the single cell level. However, the morphology and clinical cytology at the single cell level might still contribute with complementary data to more sophisticated complex studies of that topic. In addition, the morphological approach facilitates the study of the main components of single cells in various states, including the differentiation steps or ageing.

Institute of Haematology and Blood Transfusion Prague Czech Republic

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