Neutropenia is defined as a number of neutrophils, a type of granulated white blood cell, less than 1500/microliter, in the body. It is multifactorial in origin as either by decreased production, sequestration from endothelium and tissues, and increased peripheral destruction. Autoimmune neutropenia (AIN) is described as a reduced number of neutrophils resulting from increased peripheral destruction by antineutrophil antibodies from autoimmune disorders.  These autoantibodies are directed against cell membrane antigens present on IgG Fc receptors.
AIN can be considered as chronic neutropenia if it lasts for more than 3 months and without attributable to any etiology. Chronic neutropenia can be either idiopathic or involve other etiologies of autoimmune neutropenia. AIN is categorized as primary and secondary, according to etiology and pathogenesis. The primary form of AIN is dominant in children, and it presents commonly as a hematologic abnormality and bonemarrow hypoplasia and secondary form of AIN present in adults as autoimmune disorders, primary immune deficiencies, infections, hematologic malignancies, or drug exposure. AIN is also prevalent in post-transplant patients as well as in some neurological diseases.
The clinical manifestations of AIN may vary from being asymptomatic to life-threatening infections in individuals. In the pediatric population, it can lead to recurring infections, hematologic malignancies, and neuropsychiatric disorders.
The primary form is most prevalent in children and ranges from sole hematological disorders to severe life-threatening infections.
The secondary form is more prevalent in adults and divided into the following categories according to etiologies;
1. Systemic autoimmune disorders
2. Infectious disorders
4. Neurological disorders
Along with these disorders, certain congenital immunological diseases, bone marrow failure syndromes, and metabolic diseases in the pediatric population can also lead to chronic neutropenia and recurring infections through different mechanisms. Usually, in the pediatric population, autoimmune neutropenia presents with a minor hematological abnormality in the majority, but it presents, but in a few patients, it leads to life-threatening and recurrent infections. One of the causes of the secondary form of AIN is antineutrophil antibodies, which lead to neutropenia by peripheral destruction, bonemarrow inhibition, or apoptosis of cells.
Autoimmune neutropenia (AIN) and chronic idiopathic neutropenia (CIN) are relatively rare conditions, which can sometimes present as primary hematological disorders, and that's why referred to as "primary" or "isolated" neutropenia. According to a U.S. study, the prevalence of isolated neutropenia was reported to be 0.44% among Mexican-Americans, 0.84% among whites, and 4.5% among black participants. According to the same study, the prevalence of chronic severe neutropenia was estimated to be 5 cases per million in the Washington state of the USA.
In children, the primary AIN lasts for 3 to 5 years, with an average of 17 months. The frequency of primary and secondary autoimmune neutropenia is 12.85% and 3.84%, respectively, in preterm babies, according to a study done in Italy. At the time of analysis, 74.9% of primary AIN and 7.7% of secondary AIN had recovered from neutropenia. So the study concluded that primary AIN is benign and occurs in children less than 2 to 3 years of age, and secondary AIN is more severe and occurs after 5 years of age with a greater tendency to be chronic.
A study concluded striking predominance of females to males as evidenced by an 8:1 ratio, while in children, more male predominance was seen. The patients with CIN or AIN enrolled in the Severe Chronic Neutropenia International Registry in North America (SCNIR) suggested an early childhood peak with female predominance was seen.
Mature neutrophils are derived from precursor cells in the bone marrow. The total neutrophil count is divided into bone marrow, blood, and tissues. In blood, neutrophils are divided into either peripheral or circulating compartments. The peripheral neutrophils are attached to vascular endothelium, and circulating neutrophils are present in circulation through the bloodstream. Autoimmune neutropenia is a heterogeneous group of disorders with the destruction of neutrophils from the production of IgG antibodies against Fc receptors of neutrophils leading to peripheral destruction and splenic clearance.
In primary neutropenia, a decrease in the number of neutrophils leads to several infections with bacteria and fungi, but it is usually milder form than chemotherapy-induced neutropenia. The peripherally attached neutrophils to vascular endothelium play a vital role in the inflammatory response to a foreign antigen leading to an inflammatory response. For this, they need to get attached to the vessel wall, which is done by certain adhesion molecules called beta-2 integrin and spectrin. These molecules are deficient in a congenital disorder called leukocyte adhesion deficiency (LAD) and lead to a disease ranging from recurrent infections to severe life-threatening infections and delayed cord prolapse etc.
Chronic granulomatous disease is another congenital abnormality that leads to recurrent infections with catalase-positive organisms: Staphylococcus, Serratia, Burkholderia, Aspergillus, etc. Because of the absence of NADPH oxidase enzymes complex, it helps in the formation of reactive oxygen species during the respiratory burst phenomenon. Another congenital form of primary AIN is Chediak Higashi syndrome, an autosomal recessive disease, characterized by abnormal chemotaxis and failure of lysosomes to fuse with phagosomes.
The available evidence for inflammatory bowel disease suggests that the dysfunctioning innate and adaptive immunity pathways of the immune system are corresponding to an aberrant inflammatory response, and it was divided into two major types: Crohn disease has been considered to be associated with T-helper cells I response, and ulcerative colitis is considered to be driven by non-conventional T-helper cells II response.
In the case of LAD, the biopsy of inflammatory tissue shows absence or paucity of neutrophils, also remains of umbilical cord show decreased number of neutrophils and less inflammatory response showing decreased edema.
Chediak Higashi syndrome histologically shows giant lysosomal granules in the cells.
In ulcerative colitis (UC), there is a presence of inflammatory infiltrate in lamina propria with an absence of neutrophils, crypt abscesses, and cryptitis. In UC, there is an abundance of plasma cells at the base of crypts and exposed muscularis mucosa as a result of ulceration, or it may be covered in granulation tissue.
Autoimmune neutropenia (AIN) and chronic idiopathic neutropenia (CIN) are multifactorial in etiology. Basically, in children, the primary form is seen, and in adults, the secondary form is seen. Primary form in children is mild and resolves after a few years of life in the majority, while in adults, it represents a chronic entity. The history of the following is seen in both:
The investigation of autoimmune neutropenia and chronic idiopathic neutropenia includes immunoglobulins, complement system, inflammatory markers, and phagocytes functions. For the diagnosis of AIN, the detection of antineutrophil antibodies is important, but because the detection of antineutrophil autoantibodies is difficult, a combination of immunofluorescence and agglutination test for screening is used.
Quantitative Serum Immunoglobulins
Nitroblue tetrazolium (NBT) test (before and after stimulation with endotoxin)
Blood Lymphocyte Subpopulations
Lymphocyte Stimulation Assays
Complement System Evaluation
Measurement of individuals components by immunoprecipitation tests, ELISA, or Western blotting
Complement system functional studies
Other Investigations of an Immunodeficiency Disorder
Primary AIN mainly has seen in infants, which is self-limiting over time and does not require extensive measures, but secondary AIN is common in adults, which requires antibiotics and G-CSF. Implementation of granulocyte colony-stimulating factor (G-CSF) has improved neutrophil count as well as function in certain patients with neutropenia. Also, G-CSF is a treatment of choice for severe congenital neutropenia (SCN). Hematopoietic stem cell transplant (HSCT) has been approved for a treatment when the condition does not improve with G-CSF.
Prophylactic antimicrobial agents can be used for certain congenital conditions like LAD and congenital granulomatous disease. If AIN is associated with other autoimmune diseases and severe, then treatment with corticosteroids, intravenous immunoglobulins, or immunosuppressants such as rituximab should be indicated. Allogenic bone marrow transplantation from an HLA-matched related donor is the therapy of choice for severe congenital conditions with recurrent and fatal infections. Gene therapy is recommended for some cases of neutropenia as well.
Neutropenia can be differentiated according to the etiology as either immunoglobulin disorders, complements system disorders, or disorder of neutrophil formation. Primary AIN is seen in the pediatric population with congenital disorders like chronic granulomatous disease (CGD), leukocyte adhesion deficiency (LAD), and reticular dysgenesis. Secondary AIN is more commonly seen in the adult population with disorders like systemic lupus erythematosus (SLE), and inflammatory bowel disease (IBD), etc. with pathogenesis involving antineutrophil antibodies affecting the immune system, which can be ruled out by antibody levels.
Certain immunoglobin disorders involving severe combined immunodeficiency (SCID) and common variable immunodeficiency (CVID) also present with recurrent bacterial and fungal infections involving mainly GI and respiratory system, which can be ruled out by Ig levels. Some complement system disorders like C1 esterase inhibitor deficiency can also lead to extracellular bacterial infections, which can be ruled out by testing laboratory complement and enzyme levels, and in clinical manifestations, it resembles neutropenia as well.
The prognosis of AIN depends on the etiology and age at presentation. Primary AIN in the pediatric population is suggested by recurrent infections, which are usually benign and can be treated with antimicrobial agents and if severe with G-CSF and bone marrow transplant in cases such as CGD and LAD.
Secondary AIN in the adult population is associated with decreased immunity and infections, which can be treated with antimicrobial agents, immunosuppressants, biological agents, and in severe cases, plasmapheresis. AIN and CIN, as a result of chemotherapy or drugs, resolve immediately after cessation of the treatment. While certain etiologies present with less severe mucosal infections, severe congenital conditions result in death at a young age. LAD can present with death in the first year of life, or patients with less severe LAD can live till the third decade with recurrent infections and can be managed with hematopoietic stem cell transplant.
Consanguinous couples should get genetic testing before conception, and if known to have affected children, they should be educated regarding the likelihood for their second child and, if possible, avoid pregnancy at all. Parents should be counseled regarding the affected child's care in good health and disease.
AIN and CIN are rare conditions with disease spectrum extending from minor infections to severe life-threatening infections leading to death. Thus interprofessional teams, including physicians, nurses, pharmacists, can manage these conditions with the best approach. A specialists team, including immunologists, geneticists, infectious disease specialists, and pediatricians, can manage these conditions with either prophylactic antimicrobial agents or G-CSF. These patients should be monitored closely with the complete blood cell count, blood chemistry, inflammatory markers, and immunoglobulins.
The health care providers should advise these patients regarding warning signs and symptoms for infections, as well as appropriate precautions. Patients undergoing chemotherapy should watch for signs of infections and, if possible, wear masks in public and follow handwashing measures. Pharmacists should advise of possible side effects of medications prescribed for these patients by providers.
Hence a team effort is essentially required for the well being of these patients and their quality of life.
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