Human reticulocyte maturation and its relevance to erythropoietic stress.

A comparative study of circulating human reticulocytes by phase-contrast microscopic observation and NMB staining revealed two different forms of reticulocytes which could be clearly distinguished by their distinctive morphologic appearance. These were (1) a multilobular motile form and (2) a cup-shaped nonmotile form. Sequential studies of different populations in the circulation of newborns showed that the multilobular form was the youngest and the cup-shaped form the more mature reticulocyte. The multilobular form was found in the circulation only under conditions of erythropoietic stress and could not be detected in the circulation of hematologically normal individuals. The presence of these characteristic forms in peripheral blood can be used as a reliable indicator of transient or persistent erythropoietic stress.