The level of differentiation of megakaryocyte progenitors and the subsequent modulation of megakaryocyte antigens on developing colony cells.

Human megakaryocyte development was studied in cell culture by first determining the differentiation stage of the clonable progenitor cell population and then analyzing the kinetics of expression of two megakaryocyte antigens using an immunoalkaline phosphatase system. Studies on the expression of two antigens present on megakaryocytes but not detectable on platelets (Mk-A, Mk-B) revealed that Mk-A antigen was found on megakaryocytes in colonies of less than six to eight cells at early times of cell culture. By contrast, Mk-B antigen was detected only in large megakaryocytes starting day 7 of culture and observed primarily in colonies of greater than eight cells.

Human megakaryocytes. VII. Analysis of megakaryocytes for nuclear DNA content distribution in whole marrow cell suspensions by flow cytometry.

These studies were designed to quantitate and determine the DNA content distribution of human marrow megakaryocytes using whole bone marrow. Cellular DNA content within megakaryocytic cells was established by measuring propidium iodide staining in marrow cells expressing platelet glycoprotein IIb/IIIa (Gp IIb/IIIa). These studies were based on the development of a method for rapid analysis of whole marrow cell preparations by a dual fluorescent system.

Occurrence of platelet basic protein, a precursor of low affinity platelet factor 4 and beta-thromboglobulin, in human platelets and megakaryocytes.

beta-thromboglobulin antigen, a platelet-specific secreted protein, occurs in three forms: platelet basic protein, low affinity platelet factor 4, and beta-thromboglobulin. The combined level of beta-thromboglobulin antigen in megakaryocytes, measured by radioimmunoassay, was 13 +/- 7 micrograms/10(6) cells (SD, n = 6). The relative proportions of the three forms of beta-thromboglobulin antigen present within platelets and megakaryocytes were determined in cells lysed with trichloroacetic acid to minimize artifactual proteolysis.

Aging and arteriosclerosis. Cell cycle kinetics of young and old arterial smooth muscle cells.

Intimal cell proliferation is a "hallmark" of atherosclerosis. Myointimal hyperplasia in arteries has been shown to be dependent on age after vascular endothelial denudation and injury associated with vascular transplantation. Because myointimal thickening is greater in aged rats than in younger rats, and aortic segments from old rats transplanted into young syngeneic recipients have a greater myointimal proliferative response to injury than its host environment, the authors examined the cell cycle distributions of old and young rat arterial smooth muscle cells (SMCs) by flow-cytometric analysis.