Spleen in myelofibrosis. Light micrograph of a section through a spleen that has become enlarged (splenomegaly) as a result of myelofibrosis of bone marrow. Myelofibrosis leads to bone marrow losing its ability to produce blood cells. This triggers other organs of the lymphoreticular system to revert back to their foetal ability to produce blood components (haemopoiesis). The spleen is the principal organ involved in this compensatory process and enlarges as a result.