Isolation of circulating megakaryocytes in man.

Recovery of the small numbers of megakaryocytes (MKs) known to be present in normal blood is difficult because of their low frequency. Isolation of circulating MKs was achieved using a modified filtration system in which untreated blood was passed through 5 microns polycarbonate membranes. MKs were retained while most other blood cells passed through the membranes. Four groups of MKs were identified in May Grünwald-Giemsa stained filters of blood from peripheral, central and umbilical veins and umbilical arteries. Type 1 MKs were nuclei with no visible cytoplasm. Types 2, 3 and 4 were nuclei with increasing amounts of cytoplasm. Type 4 MKs, possessing copious cytoplasm, were rarely isolated from peripheral venous blood but were more regularly encountered in central venous and cord blood. Filtration of whole blood through polycarbonate membranes is a useful technique for the isolation of circulating MKs, which are a normal physiological occurrence. Their presence is consistent with the production of platelets in the placenta during intra-uterine life, and subsequently in the pulmonary circulation.