The role of apoptosis in the pathophysiology of chronic neutropenias associated with bone marrow failure.

Chronic neutropenia syndromes associated with bone marrow (BM) failure comprise distinct congenital and acquired hematologic disorders with varying degree of neutropenia due to decreased or ineffective BM neutrophil production. Recent evidence suggests that defective granulocytopoiesis in these neutropenia states is a consequence of accelerated apoptotic cell death of BM myeloid progenitor cells and/or their differentiated progeny. Inherited or spontaneously appearing mutations in the ELA2 gene encoding for neutrophil elastase have been implicated in the accelerated apoptotic process of the BM myeloid cells in patients with cyclic and severe congenital neutropenia. A disturbed balance between pro-apoptotic and anti-apoptotic intracellular or membrane molecules such as downregulation of the bcl-2 family members or upregulation of the death receptor Fas, have been implicated in neutropenia associated with myelokathexis, Shwachman-Diamond syndrome and acquired chronic idiopathic neutropenia of adult. In this review we summarize the available evidence suggesting that abnormally increased apoptosis and impaired proliferative and differentiating properties of neutrophil progenitor and precursor cells represent a common pathogenetic mechanism for impaired granulocytopoiesis in both acquired idiopathic and congenital neutropenia states. The underlying distinct cellular and molecular abnormalities and the role of the BM microenvironment are extensively analysed.