TOPOGRAPHIC LOCALIZATION OF FIBRONECTIN IN BONE MARROW OF NORMAL HUMANS AND SOME GROUPS OF ANEMIAS AND ITS RELATION TO HEMATOPOIESIS

Abstract

Hematopoiesis is a complex process, which takes place in the adult life in the bone marrow cavities.

It's the process by which the hematopoietic cells live, home to the bone marrow microenvironment, proliferate and differentiate to the full complement of mature blood elements.

After stem cell transplantation, intravenously infused stem cells distribute widely and nonspeci fically to all organs and home to the bone marrow cavity to start a finite process of hematopoiesis.

Homing is not a passive process but it involves a very complex array of interactions between the transplanted stem cells and bone marrow microenvironment.

First cells adhere to the endothelial lining of the bone marrow sinusoids followed by penetration to the extravascular bone marrow spaces where they interact with the stromal cells and extracellular matrix, like fibronectin, through surface receptors.

In-vitro studies indicate that human hematopoietic progenitors carry fibronectin receptors including the beta-! integrin, CD49d (sometimes called VLA-4) and that fibronectin receptors are important in early homing of the stem cells post­ transplantation.

Stem cells of different sources are clinically different in their seeding and engrafment pattern. Also, recent fiowcytometry studies indicate that stem cells of different sources are different in their cytoadhesion molecules' expression, which may impact their homing and subsequently engrafment behavior.