Splenic haematopoiesis in primary (idiopathic) osteomyelofibrosis: immunohistochemical and morphometric evaluation of proliferative activity of erytro- and endoreduplicative capacity of megakaryopoiesis (PCNA- and Ki-67 staining).

Using monoclonal antibodies against proliferating cell nuclear antigen or PCNA (PC10) and the Ki-67 antigen (MIB1), an immunohistochemical and morphometric study was performed on routinely processed splenic tissue from ten patients with primary (idiopathic) osteomyelofibrosis (OMF). To determine the proliferation capacity of erythroid precursors and the endoreduplicative activity of megakaryocytes, corresponding antibodies (Ret40f and CD61) were applied in combination with the cell-cycle markers (sequential double-immunostaining). Morphometric analysis revealed no significant differences in PCNA or Ki-67 reactivity in either cell lineages. In comparison with previous studies on normal bone marrow, in splenic tissue showing myeloid metaplasia, the numbers of PCNA-labelled proerythroblasts, erythroblasts and megakaryocytes were conspicuously increased. Considering the ineffective erythropoiesis in OMF, there seemed to be a disproportional enhancement in PCNA and Ki-67 immunostaining of the red cell lineage. Similarly, the small size of megakaryocytes in advanced, OMF-associated myeloid metaplasia was in keeping with an impairment of endoreduplicative activity. In addition to various other contributory factors, anaemia in OMF may be partially caused by secondary folate (haematinic) deficiency. From experimental studies this defect is known to cause an abnormal arrest in the S-phase of the cell-cycle, comparable to that characterising pernicious anaemia. As a sequel of this pathomechanism, an undue overexpression of PCNA and Ki-67 has to be assumed, that is not necessarily associated with DNA synthesis or cell cycling.