Chapter 31: Disorders of Neutrophil Functions

• Antibody or complement defects

• Abnormalities of cytoplasmic movement (chemotaxis and phagocytosis)

• Abnormal microbicidal activity

• See Table 31–1 for features of the major abnormalities of neutrophil function

• Interactions between antibodies and complement generate opsonins and stimulate chemotactic factor development.

• C3 deficiency (autosomal recessive inheritance) results in the most severe disorder.

• Homozygotes have no detectable C3 and suffer severe recurrent bacterial infections.

• Deficiency of other less centrally active complement proteins results in a milder condition.

• C3b inactivator or properdin deficiency results in deficiency of C3 also.

• Affected individuals usually suffer from infections due to encapsulated organisms.

Chédiak-Higashi Syndrome

Pathogenesis

• This syndrome is a rare autosomal recessive disorder of abnormal, increased granule fusion with generalized cell dysfunction, resulting in defects in chemotaxis, degranulation, and microbicidal activity.

• The cause is mutation in LYST gene on chromosome 1q.

• There is increased membrane fluidity in Chédiak-Higashi neutrophils, monocytes, and natural killer cells.

• Spontaneous fusion of granules results in huge lysosomes with diluted hydrolytic enzymes.

• Phagocytosis and the respiratory burst are normal, but killing of organisms is slow.

• Neutropenia occurs as a consequence of precursor death (apoptosis) in the marrow.

Clinical Features

• Because of abnormal association of melanosomes, decreased pigment is noted in skin, hair, iris, and ocular fundus. Light skin, silvery hair, solar sensitivity, and photophobia is characteristic.

• Total leukocyte counts average about 2 × 10⁹/L, and neutrophil counts range from 0.5 to 2.0 × 10⁹/L.

• Neutrophils and monocytes have impaired microbial killing as a result of inconsistent delivery of diluted granule contents into phagosome.

• Natural killer cell dysfunction may contribute to the predisposition to infection.

• Infections are common, primarily involving mucous membranes, skin, and the respiratory tract. Various bacteria and fungi are involved, but Staphylococcus aureus is the most common.

• Peripheral neuropathies (sensory and motor), cranial neuropathies, and autonomic dysfunction occur, as well as ataxia.

• Platelet counts are normal, but impaired platelet aggregation, storage pool deficiency, and prolonged closure times are common.

• An accelerated phase may occur at any age, characterized by rapid lymphocytic proliferation (not neoplastic) resulting in a syndrome of hepatosplenomegaly, lymphadenopathy, and high fever in the absence of bacterial infection. Subsequently, pancytopenia and a high susceptibility to infection usually lead to death. The syndrome is the result of an inherited predisposition to hemophagocytic lymphohistiocytosis, probably related to the inability to contain Epstein-Barr virus infection.

Laboratory Features

• In addition to the characteristic phenotypic features noted above, the principal confirmatory test is the presence of giant granules in neutrophils on the blood film. Molecular testing is not generally available. Heterozygotes are normal and cannot be detected clinically or biochemically.

Treatment

• High-dose ascorbic acid (200 mg/d in infants, 2 g/d in adults) is usually prescribed in the stable phase and improves the clinical state in occasional patients.

• Infections are treated as they arise. Prophylactic antibiotics are generally not useful.

• The only curative treatment is allogeneic hematopoietic stem cell transplantation from a histocompatible donor. The hematologic, immunologic, and natural killer cell abnormalities are corrected by successful transplantation. Other cell abnormalities are not.

• In the accelerated phase, vincristine and glucocorticoids have been used but are not clearly efficacious.

Specific Granule Deficiency

• This exceedingly rare autosomal recessive disorder is characterized by bilobed neutrophils lacking specific granules on the blood film and “empty” specific granules on transmission electron microscopy.

• Vitamin B₁₂-binding protein, lactoferrin, and collagenase are absent from specific granules. Defensins are absent from primary granules. Gelatinase activity is absent from tertiary granules. Microbicidal activity is moderately impaired because of a lack of defensins and lactoferrin.

• Chemotaxis is abnormal because of a lack of adhesion molecules in tertiary and specific granules.

• Eosinophil granule proteins are also deficient (major basic protein, eosinophilic cationic protein, eosinophil-derived neurotoxin). Thus, this disorder is a global abnormality of phagocyte granules and is not limited to neutrophil specific granules as its name implies.

• The diagnosis can be confirmed by a severe deficiency of lactoferrin or B₁₂-binding protein in the plasma.

• Recurrent skin and pulmonary infections are common, usually from infection with S aureus and Pseudomonas aeruginosa. Candida albicans infections also may occur.

• Treatment is supportive. Antibiotics for acute infections and surgical drainage of chronic abscesses.

Leukocyte Adhesion Deficiency-I

• This rare, autosomal recessive disease is characterized by delayed detachment of umbilical cord, delayed wound healing, frequent severe periodontal or soft-tissue infection, and markedly decreased pus formation despite blood neutrophilia.

• The underlying defect is decreased or absent expression of the β₂ integrin family of leukocyte adhesion proteins (CD11/CD18 complex). These integral membrane glycoproteins (including LFA-1, Mac-1, and p150,95) have noncovalently bonded α and β subunits. Several mutations in the gene encoding the β subunit have been found; these mutations result in profoundly impaired chemotaxis or phagocytosis; degranulation and the respiratory burst are diminished. As a result, the neutrophils can enter the circulation but cannot egress into the tissues.

• See Table 31–2 for features of leukocyte adhesion deficiency disorders.

• Blood neutrophil concentrations are markedly elevated (15–60 × 10⁹/L), but cells do not enter tissues. Neutrophil concentrations may increase to as high as 150 × 10⁹/L if patient is infected.

• Typically, there is marrow granulocytic hyperplasia and blood neutrophilia. Diagnosis is made by flow cytometric measurement of CD11a, CD11b, CD11c, and CD18 on neutrophils. Decreased expression of these surface molecules is the characteristic finding.

• Severely affected patients have recurrent and chronic soft-tissue infections (subcutaneous and mucous membranes). S aureus, Pseudomonas spp., other gram-negative enteric rods, and Candida spp. are the usual offenders.

• Prophylactic trimethoprim-sulfamethoxazole lowers the risk of recurrent infection.

• Treatment of choice for the severely affected is allogeneic hematopoietic stem cell transplantation.

Neutrophil Actin Dysfunction

• Abnormal chemotaxis and phagocytosis are expressed as neonatal recurrent severe bacterial infections.

• Defective actin polymerization occurs; an intracellular inhibitor of polymerization has been isolated.

• This rare lethal disease requires allogeneic hematopoietic stem cell transplantation.

Familial Mediterranean Fever

• This autosomal recessive disease primarily affects populations surrounding the Mediterranean basin. It is the result of a mutation in the PYRIN gene expressed primarily in leukocytes and synovial and peritoneal fibroblasts.

• The gene mutation may be identified by polymerase chain reaction methodology.

• The pathogenesis is a predisposition for neutrophils to migrate to serosal surfaces, accumulate, and generate an inflammatory response.

• The disease is characterized by acute limited attacks of fever, often accompanied by pleuritis; peritonitis; arthritis; pericarditis; inflammation of the tunica vaginalis of the testes; and erysipelas-like skin disease on the lower leg, ankle, or dorsum of the foot.

• Arthralgia and monarticular arthritis can accompany febrile attacks.

• Approximately 25% of affected patients develop renal amyloidosis. This finding can progress to renal failure and may be the cause of death.

• Prophylactic colchicine, 0.6 mg orally, two to three times a day, prevents or substantially reduces the acute attacks in most patients. Some patients, who have prodromes, can abort attacks with doses of colchicine beginning at the onset of attacks (0.6 mg orally every hour for 4 hours, then every 2 hours for four doses, and thereafter every 12 hours for 2 days).

Other Disorders of Neutrophil Motility

• Neonatal neutrophils have impaired β₂ integrin function with abnormal transendothelial movement.

• Direct inhibitors of neutrophil motility include ethanol and glucocorticoids.

• Circulating immune complexes also inhibit motility by binding to neutrophil Fc receptors.

Hyperimmunoglobulin E Syndrome

• This syndrome is usually an autosomal dominant disorder as a result of mutations in STAT3 gene.

• Patients have markedly elevated serum IgE levels, chronic eczematoid dermatitis, and recurrent bacterial infections (skin abscesses, sinusitis, otitis media, pneumonia). They may also have coarse facial features, growth retardation, and osteoporosis.

• Coarse facial features include prominent forehead, broad nasal bridge, wide nasal tip, prognathism, hyperextensible joints, and scoliosis may be present. Delayed shedding of primary dentition occurs.

• Chemotaxis is impaired, but the molecular mechanism is unknown.

• Serum IgE levels usually exceed 2000 IU/mL, but, as opposed to atopic patients, most of this antibody is directed against S aureus.

• Marked blood and sputum eosinophilia are constant features. Poor antibody responses to neoantigens is also seen.

• Prophylactic trimethoprim-sulfamethoxazole is used to minimize frequency of S aureus infections.

• Early diagnosis and staphylococcal antibiotic prophylaxis can markedly improve the prognosis.

• Topical glucocorticoids may reduce symptoms of the eczematoid dermatitis.

• Orthopedic care for scoliosis, fractures, and degenerative joint disease, as well as dental care for delayed loss of first dentition are important.

• Incision and drainage of abscesses and superinfected pneumatoceles may be necessary.

Chronic Granulomatous Disease (CGD)

• Neutrophils and monocytes have impaired production of superoxide, with markedly reduced microbicidal activity.

• CGD is caused by mutations in any of the genes encoding the NADPH oxidase, an electron transport chain that catalyzes the formation of superoxide.

• About two-thirds of patients inherit the neutrophil defect as an X chromosome–linked abnormality. The remaining patients have several types of autosomal inheritance.

• In the resting state, the oxidase components are in two locations. The membrane-bound portion, cytochrome b558, is composed of two subunits: gp91-phox and p22-phox. The heavy chain has binding sites for heme, FAD, and NADPH. Three other proteins reside in the cytosol, but on stimulation, move to the membrane and interact with gp91-phox. These are p47-phox, p67-phox, and a GTP-binding protein. Severity of CGD depends on which of these components is affected. The most frequent form is due to mutation of gp91-phox gene on chromosome Xp21.1. Other mutations also cause CGD but occur less frequently. See Table 31–3 for the genetic and molecular classification of CGD.

Pathogenesis

• Normally, neutrophils form hydrogen peroxide, which acts as substrate for myeloperoxidase to oxidize chloride to hypochlorous acid and chloramines. These accumulate in the phagosome and kill the microbe.

• Oxidase activation acutely produces an alkaline phase in the phagosome that is important for function of neutral hydrolases. In CGD cells, this alkaline phase does not occur, impairing the enzymes that digest bacteria.

Clinical Features

• The X-linked form can be evident in the first months of life, whereas autosomal forms may not be diagnosed until adulthood.

• Skin abscesses, recurrent lymphadenitis, dermatitis, pneumonias, osteomyelitis in small bones of hands or feet, and bacterial hepatic abscesses are each common and require consideration of chronic granulomatous disease. See Table 31–4.

• Organisms commonly involved are S aureus, Aspergillus sp, and C albicans (see Table 31–4).

• Granulomata are common and cause chronic lymphadenopathy.

Laboratory Features

• For diagnosis, neutrophil superoxide or hydrogen peroxide generation is measured in response to soluble and particulate stimuli. Readout can be done using flow cytometry with dihydrorhodamine-123 label. The generation of hydrogen peroxide is used because it increases fluorescence on oxidation as an indicator of oxidative product formation.

• In addition, the nitroblue tetrazolium (NBT) test can be used. In normal neutrophils, NBT is reduced to purple formazan, and this assay is read by microscopic examination of individual neutrophils for purple formazan crystals. With most forms of CGD, no reduction to the purple color occurs.

• The NBT test can also detect the X-linked carrier state, because a varied percentage of cells will be NBT-negative and the remainder of the cells will be NBT-positive (mosaicism).

• More sophisticated procedures can define the molecular defect.

• Rare severe forms of glucose-6-phosphate dehydrogenase deficiency can mimic CGD; NADPH is inadequate for normal superoxide generation.

Therapy and Prognosis

• Treatment consists of long-term trimethoprim-sulfamethoxazole prophylaxis, appropriate antibiotics for particular infections, and surgical management of abscesses.

• Interferon-γ (50 μg/m², three times per week by subcutaneous injection) has been found to decrease the number of serious bacterial and fungal infections.

• The only curative therapy is allogeneic hematopoietic stem cell transplantation.

• Some affected persons and carriers who have only a small percent of normal functioning neutrophils have mild disease and a much better prognosis. This finding is most common in X chromosome–linked forms. Gene therapy is being studied, because one could predict that a very small increase in normally functioning neutrophils (eg, 5%) might significantly ameliorate the disease.

Myeloperoxidase Deficiency

• This common autosomal recessive disorder has a prevalence of 1:2000 in the general population.

• Myeloperoxidase (MPO) is absent in primary granules of neutrophils and monocytes (but not eosinophils).

• MPO catalyzes formation of hypochlorous acid; the MPO-deficient neutrophil is slower to kill ingested organisms, but after 1 hour, microbicidal activity is similar to normal as a result of MPO-independent killing systems in the cell.

• The disorder usually does not lead to increased susceptibility to infection.

• In a few patients with diabetes mellitus and MPO deficiency, severe infection with Candida sp has occurred.

• Acquired MPO deficiency can be seen in lead intoxication, myelodysplasia, acute myelogenous leukemia, and ceroid lipofuscinosis.

• Frequent bacterial infections should alert the clinician to the possibility of a functional neutrophil defect. Many of the tests used to evaluate neutrophils are bioassays, so are subject to great variability; they must be interpreted with caution, always in light of the patient’s clinical condition. These tests are reviewed in Figure 31–1.