It is not known with certainty whether the production of neutrophils in the mitotic compartment exactly equals the neutrophil turnover rate. Studies in dogs have suggested that some immature neutrophils die in the marrow (“ineffective neutrophilopoiesis”).46 Ineffective neutrophilopoiesis has not been shown in normal humans, however,13,47 although ineffective neutrophilopoiesis occurs in some pathologic states. In the preleukemic syndromes48 there is probably substantial intramedullary cell death, as may occur also in myelofibrosis and perhaps some of the idiopathic neutropenic disorders. At present, however, there is no convenient means to quantitate ineffective neutrophilopoiesis.
On completion of maturation, the neutrophils are stored in the marrow and are referred to as the mature neutrophil reserve. This reserve contains many more cells than are normally circulating in the blood. Comparative data on the characteristics of the maturation-storage compartment are given in Table 66-2. Under stress, maturation time may be shortened, divisions may be skipped, and release into the blood may occur prematurely.
MHC (major histocompatibility complex): A genetic region encoding molecules involved in antigen presentation to T-cells. Class I MHC molecules are present on virtually all nucleated cells and are encoded mainly by the H-2 K, H-2D, and H-2 L loci in mice and by HLA-A, HLA-B, and HLA-C in humans, while class II MHC molecules are expressed on antigen-presenting cells (primarily dendritic cells, macrophages, and B-cells) and are encoded by H-2A and H-2E in mice and HLA-DR, HLA-DQ, and HLA-DP in humans. Allelic differences are associated with the most intense graft rejection within a species.