Neutrophils play an essential role in immune defenses because they ingest, kill and digest invading microorganisms, including fungi and bacteria. Failure to carry out this role leads to immunodeficiency that is mainly characterized by the presence of recurrent infections. Defects in neutrophil function can be quantitative as seen in neutropenia or qualitative as seen in neutrophil dysfunction. The standard circulating neutrophil count is above 1.5 x 10/L. Neutropenia can be classified in asymptomatic (mild), moderate and severe and thus the progression to infection concerning the number.
Neutropenia with decreased production with marrow hypoplasia can be primary and due to chronic benign neutropenia, cyclical neutropenia and other congenital and familial neutropenias. It can be secondary to cytotoxic drugs, aplastic anemia, leukemia, drug reactions, and infections. Neutropenia with increased destruction with marrow hyperplasia is due to hypersplenism and immune neutropenia. Secondary causes are the commonest, for example, neutropenia caused as a side effect of chemotherapy for malignancies. Congenital forms are rare and vary in severity, some of them are life-threatening conditions including leukocyte adhesion deficiency, Chediak-Higashi syndrome, hyper-IgE, recurrent infection syndrome, and chronic granulomatous disease.
Hsieh and collaborators reported that in the United States, the prevalence of neutropenia was 0.38% among Mexican-Americans, 0.79% among whites, and 4.5% among black participants. Weycker and collaborators reported that the risk of febrile neutropenia during the chemotherapy regimen course for treating solid tumor was 16.8%. Severe neutropenia was present in 1 of every 2 patients with lymphoma receiving chemotherapy with a higher risk of febrile neutropenia, and it was found in approximately 1 of every 10 breast cancer patients in Spain.
Neutrophils play a role in the immune defense against extracellular bacteria including Staphylococci, Streptococci, Escherichia coli among others. They also protect against fungal infections including those produced by Candida albicans. Once their count is below 1 x 10/L recurrent infections start. As compensation, the monocyte count may increase. In primary neutropenia disorders such as chronic granulomatous disease presents with recurrent infections affecting many organs since childhood. It is caused from a failure to produce toxic reactive oxygen species so that the neutrophils can ingest the microorganisms but they are unable to kill them, as a significant consequence granuloma can obstruct organs such as the stomach, esophagus, or bladder. Patients with this disease are very susceptible to opportunistic infections by certain bacteria and fungi, especially with Serratia and Burkholderia.
Leukocyte adhesion deficiency has an autosomal recessive inheritance, and its functional defect is a failure of neutrophils to adhere to endothelial cells and so to traverse into tissues to ingest and kill bacteria. Chediak-Higashi syndrome is also an autosomal recessive problem, characterized by abnormal chemotaxis, so neutrophils fail to reach bacteria, and reduced microbicidal activity as lysosomes fail to fuse with phagosomes.
In Chediak-Higashi syndrome histologically present with giant lysosomal granules in secretory cells. The chronic granulomatous disease is characterized by the presence of granulomas, which are composed by histiocytes that can fuse to form multinucleated giant cells and might be surrounded by other immune cells such as lymphocytes and cover with collagen.
Quantitative Serum Immunoglobulins
Blood Lymphocyte Subpopulations
Nitroblue tetrazolium (NBT) test (before and after stimulation with endotoxin)
Complement System Evaluation
Measurement of individuals components by immunoprecipitation tests, ELISA, or Western blotting
Complement system functional studies
Other investigations of immunodeficiency disorders
Application of granulocyte-colony stimulating factor (G-CSF) can improve neutrophil functions and number. Prophylactic use of antibiotics and antifungals is reserved for some forms of alteration in neutrophil function such as chronic granulomatous disease CGD). The utilization of antimicrobials is compulsory if recurrent infections exist. Interferon-gamma has been successfully used to improve the quality of life of the patient suffering from neutropenia. Allogenic bone marrow transplantation from an HLA-matched related donor can cure CGD but has a high mortality rate, and gene therapy is also a therapeutic option for treating disorders with neutropenia. Furthermore, intravenous immunoglobulins can be another option in the management of these disorders.
Neutropenia can differentiate from antibody deficiency disorders, where a class or different classes of immunoglobulins are below the normal range or absence. These disorders may present clinically by recurrent infections with bacteria and fungi, some of them are opportunistic pathogens, so the use of antimicrobials to treat infectious diseases is a norm. A patient with neutropenia may have an intact acquired immune response but a low number or impaired function of neutrophils. Some complement system deficiency, e.g., C3 deficiency manifests with multiple extracellular bacterial infections and may resemble neutropenia, but can rule out by quantification and functional assessment of the complement system.
The prognosis of neutropenia disorders base on the cause and organs involved. CGD has a better prognosis if allogenic bone marrow transplantation can successfully achieve. Neutropenia due to chemotherapy or drugs may cause remission once the treatment is over. Some primary defects of neutrophil functions affect the prognosis, where devastating fatal diseases can lead to death in young age.