Factor XIII: a marker of mono- and megakaryocytopoiesis.

Previous studies have shown that human platelets, megakaryocytes and peripheral blood monocytes contain the subunit a of plasma factor XIII (FXIII) which plays a key role in fibrin stabilization. To study the expression of FXIII subunit a during differentiation of the mono- and megakaryocytic cell lines, bone marrow smears were examined by immunomorphological methods. In addition to megakaryocytes, FXIII was detected in a large number of cells by a highly sensitive immunoperoxidase staining. Characterization of these cells was carried out by double immunofluorescent labelling in which the detection of FXIII subunit a was combined by the labelling of either Leu M3 monocyte/macrophage surface antigen or platelet factor 4 (PF4) a marker for megakaryocytic cells. On the course of differentiation from early precursors to mature megakaryocytes all phenotypic form of the megakaryocytic cell line expressed FXIII subunit a though there were considerable changes in its subcellular distribution pattern. Leu M3 positive cells of monocytopoiesis, i.e. monocytes and promonocytes and in all probability monoblasts as well, were also labelled for FXIII. On this basis FXIII subunit a could be considered as a common marker of megakaryo- and monocytopoiesis and its immunomorphological detection might provide a useful diagnostic tool for identifying normal and perhaps also malignant differentiation forms of these cell lines.