Neutrophils play important roles in immunity and wound healing; their primary function is ingesting and killing pathogens.Neutrophil disorders can result from deficient cell numbersor defective function (Table 74-1). Patients with neutrophildisorders are susceptible to a variety of bacterial infectionsand certain fungi. Suggestive signs include mucous membrane infections (gingivitis), abscesses in the skin and viscera,lymphadenitis, poor wound healing, delayed umbilical cordseparation, or absence of pus. Neutrophils develop in the bonemarrow from hematopoietic stem cells by the action of severalcolony-stimulating factors, including stem cell factor, granulocyte-monocyte colony-stimulating factor, granulocyte colony-stimulating factor (G-CSF), and interleukin-3. On leavingthe bone marrow, mature neutrophils are found in the circulation or reside in the marginating pool. Adhesion molecules arenecessary for neutrophils to roll and adhere to vascular endothelium and extravasate from the blood into sites of infection, where they phagocytose and kill pathogens, especially thosecoated by complement or antibodies. Chemotactic factors, including the complement fragment C5a, interleukin-8, andbacterial formulated peptides, mobilize neutrophils to enter tissues and sites of infections. Neutrophils kill ingested pathogensusing granular enzymes or by activation of oxygen radicals.
Disorders of Neutrophil Numbers
Available @ StudentConsult.com
Diarrhea Neutropenia Failure to Thrive
The normal neutrophil count varies with age. Neutropenia is defined as an absolute neutrophil count (ANC) less than 1500/mm3 for white children 1 year of age or older. African American children normally have lower total white blood cell and neutrophil counts. The effect of neutropenia depends on its severity. The susceptibility to infection is minimally increased until the ANC is less than 1000/mm3. Most patients do well with an ANC greater than 500/mm3. At these levels, localized infections are more common than generalized bacteremia. Serious bacterial infections are more common with an ANC less than 200/mm3. The major types of infections associated with neutropenia are cellulitis, pharyngitis, gingivitis, lymphadenitis, abscesses (cutaneous or perianal), enteritis (typhlitis), and pneumonia. The sites of the infection usually are colonized heavily with normal bacterial flora that becomes invasive in the presence of neutropenia. Neutropenia may be congenital or acquired (Table 74-2) and may be associated with specific diseases, especially infections (Table 74-3), or result from drug reactions (Table 74-4).