Leukocytosis
Leukocytosis means an increase in the number of white blood cells, leukocytes. This is caused by several reasons. The amount of precursor cells found in the bone marrow, circulation and tissues. The rate of release of cells from these staorage pools. The percentage of cells found rolling on the blood vessel wall. And the extravasation of cells out of the blood into the tissues, where they would not be counted in a blood sample.
The amount of white blood cells in the circulation is dictated by regulating the homeostasis of cytokines, growth factors and adhesion molecuels which directly influence the above mentioned reasons of leukocytosis. In an acute infection, the release of numerous cytokines from inflammatory cells and innate immune system cells, stimulates the bone marrow stromal cells and T cells to produce increased amounts of an additional, more potent factor, colony-stimulating factors, which enhancethe doubling and differentiation of many cells, but mainly committed granulocyte progenitors, leading to an increase in neutrophil counts in an infection. The cytokines that cause this increase are mainly IL-1 and TNF in neutrophils. An increase in IL-5 would lead to eosinophilia, while an increase in IL-7 would lead to lymphopoiesis. In sepsis or severee inflammatory diseases, not only is there an elevation of white blood cells, but there are also changes in their morphology. These include toxic granulations, coarse and dark granules that are postulated by many to be abnormal azurophilic granules, Dohle bodies which are dilated endoplasmic reticulum that appear blue in Wright-Giemsa stains, and cytoplasmic vacuoles. These changes are seen in neutrophils.
This is not a problem, unless if it is in a child suffering from a viral infection that is acute where it is common to see normal lymphoid cells that resemble neoplastic cells. Moreover, in any patient with a chronic infection or inflammatory state, many immature granulocytes usually appear in the blood. Differentiation with acute myelogenous leukemia in this instance can be difficult.
1) Robbins and Cotran Pathologic Basis of Disease. Seventh Edition. Kumar, V., Abbas, A.K., and Fausto, N. 2005, Elsevier Inc.