Accumulation and Massive Cell Death of Polymorphonuclear Neutrophils in the Developing Bone Marrow of the Mouse: A Histological Study

Abstract

Accumulation and cell death of neutrophils were studied by light and electron microscopy in neonatal mouse bone marrow. At the beginning of bone marrow hematopoiesis, the marrow cavity contained a large number of polymorphonuclear leukocytes. Polymorphs comprised approximately 75% of the total nucleated cells in the hematopoietic compartment of the newborn marrow, the majority being neutrophils. Mature neutrophils were sometimes crossing the endothelium of the marrow blood sinus. Neutrophils in neonatal marrow show features typical of apoptosis, e.g. formation of nuclear pockets and blebs, margination of compact nuclear chromatin to form sharply circumscribed masses, condensation of cytoplasm, and convolution of cell outlines. Dying neutrophils were devoured and digested by phagocytes. The occurrence of large-scale neutrophil death and removal of neutrophils by phagocytes in neonatal bone marrow are discussed in relation to programmed cell death in development of the fetal hematopoietic system.