Fibronectin-mediated attachment of hematopoietic cells to stromal elements in continuous bone marrow culture.

Hematopoiesis in continuous bone marrow culture is dependent upon close-range interaction between hematopoietic cells and marrow-derived adherent cells. The latter have been shown to include a significant proportion of fibroblastic elements, synthesizing the attachment protein fibronectin. The role of fibronectin in continuous bone marrow culture was therefore investigated. Continuous marrow cultures were stained by the peroxidase-anti-peroxidase technique, using an affinity-purified anti-fibronectin antibody. The stained cultures were then examined by transmission electron microscopy for the presence of fibronectin at sites of cellular attachment. Fibronectin was detected on the substratum attachment surfaces of marrow-derived adherent cells and at sites of interaction between stromal elements in the adherent layer. Fibronectin was also detected at many attachment sites between marrow-derived adherent cells and developing granulocytes and monocytes. The possible significance of these observations is discussed in relation to the hematopoietic microenvironment.