Endothelial cell proliferation in myelofibrosis.

The distribution of laminin and collagen type IV in normal human bone marrow appeared to be limited to a small number of capillary and sinusoidal basement membranes. Cellular elements including megakaryocytes showed a negative staining reaction. In contrast, myelofibrotic bone marrow showed markedly increased quantities of both laminin and collagen type IV. This was consistent with a proliferation of endothelial cells within the marrow as confirmed by factor VIII RAG staining. It is suggested that in myelofibrosis in addition to a marked fibrous reaction proliferation of vascular elements is also prominent.