CONSECUTIVE APPEARANCE OF COAGULATION-FACTOR-XIII SUBUNIT-A IN MACROPHAGES, MEGAKARYOCYTES, AND LIVER-CELLS DURING EARLY HUMAN-DEVELOPMENT

Thirty embryonic and fetal samples were investigated to study the appe arance and characteristics of factor XIII subunit A (FXIIIA)-containin g cells in the course of human development. Samples were either vacuum -embedded in paraffin for staining FXIIIA by a sensitive biotin-strept avidin system or snap-frozen for double-labeling studies to characteri ze FXIIIA-containing cells. FXIIIA appeared as early as the fifth gest ational week in yolk sac samples in stellate-shaped cells. Nonparenchy mal cells in liver samples showed intense labeling for FXIIIA from the sixth week of gestation. The relative amount of FXIIIA-containing cel ls rapidly diminished up to the 13th gestational week. When characteri zed, the majority of these cells proved to be KiM7-positive macrophage s, while GPlb (CD42b)-labeled cells accounted for less than 10% of FXI IIA-positive cells. Liver cells did not show any staining for FXIIIA i n first trimester samples. The earliest liver specimen showing FXIIIA was at the 20th week, when FXIIIA appeared in some liver cells, partic ularly in those surrounding the central veins. In bone marrow smears, FXIIIA-positive cells started to appear at week 10 in the clavicles an d increased in number in subsequent stages of development. Intracellul ar FXIIIA was distributed between GPlb-, RFD7-, and KiM7-positive cell s. The results indicate that, apart from liver cells, at least three d ifferent cell populations (KiM7(+) RFD7(+) GPlb(-), KiM7(-) RFD7(-) GP lb(-), and KiM7(-) RFD7(-) GPlb(+)) contain FXIIIA in the early phase of human development. We conclude that FXIIIA appears very early durin g human development and is detectable in both extra- and intraembryoni c hematopoietic organs. Intracellular FXIIIA in early human developmen t is distributed between different macrophages and megakaryocytes, and by week 20, it appears in liver cells as well. (C) 1995 by The Americ an Society of Hematology.