Ultrastructural studies of intercellular contacts (junctions) in bone marrow. A review

This paper reviews ultrastructural studies of the intercellular contacts or junctions between cells of the bone marrow. Studies using tannic acid and glutaraldehyde as a fixative have shown pentalaminar complexes between many types of cells in marrow of mice and chicks. These intercellular contacts occur between adjacent stromal cells, between stromal cells and developing blood cells and, in marrow of mice, between migrating blood cells and cells of the sinusoidal wall. Because of their location and widespread occurrence, it is believed these contacts may represent a type of adherent junction helping to maintain an orderly arrangement of blood cells and stromal cells in the marrow. Migrating blood cells may use these contacts as anchoring sites during locomotion toward the sinusoids and in crossing the sinusoidal wall. On the other hand, since these junctions resemble gap junctions of other tissues, one should not exclude the possibility that they are involved in cellular communication. Freeze-fracture and lanthanum impregnation studies have failed to demonstrate these junctions in marrow. Studies using ruthenium red have shown apparent sites of attachment between cells of the marrow, but it is not known whether these sites correspond to the intercellular contacts seen in tannic acid preparations.