Reticulocyte motility and form: studies on maturation and classification.

A new two-stage living cell cytological classification is presented for reticulocytes in the rat and shown on an overall population basis to be the equivalent of the classical new methylene blue staining characterization. Class 1 reticulocytes (R1) are motile and multilobular. They comprise about 25% of normal bone marrow reticulocytes, but none of the reticulocytes in normal blood. Class 2 reticulocytes (R2) are asymmetrically "deep dished" in appearance and contain visible refractile granules, viewed in phase-contrast microscopy. In animals "stimulated" by bleeding, the percentage of motile marrow reticulocytes is found to be a linear function of hematocrit over the range of about 25%-70% total reticulocytes. In the blood, the associated maximum rise of class R1 is only to about 8%. These and related cellular properties are discussed with respect to the maturation and release of normal reticulocytes. Applicability of this work to studies on humans and to pathology is also indicated.