Nonmalignant Disorders of Leukocytes Part 4

Eosinophil Structure

The granules of eosinophils contain strongly basic proteins and stain intensely with acid dyes. They have a striking and unique appearance on electron microscopy [see Figure 1]. The granules consist of an electron-dense core surrounded by a relatively radiolucent matrix; eosinophil peroxidase is active in the matrix. The dense core has a crystalloid structure and contains eosinophil cationic proteins (ECPs), major basic proteins (MBPs), and eosinophil-derived neurotoxins. MBPs and ECPs are capable of inflicting considerable damage to parasites such as schisto-somula by binding to and disrupting their cell membranes. In addition, MBPs enhance the adherence of eosinophils and neu-trophils to schistosomula.62

Table 6 Lysosomal Storage Diseases

Disease (Common Name)	Inheritance	Enzymatic Defect	Organs and Tissues Involved	Stored Material
Metachromatic leuko-
dystrophy (MLD)
Infantile MLD	Locus: 22q13.3-qter	Arylsulfatase A	Brain, peripheral nerves	Sulfatide
Juvenile MLD	Locus: 10q22	Arylsulfatase A	Brain, peripheral nerves	Sulfatide
Adult MLD		Arylsulfatase A, saposin B deficiency	Brain, peripheral nerves	Sulfatide
Pseudodeficiency		Partial arylsulfatase A	Normal	None
Multiple sulfatase deficiency		Unknown primary defect, multiple lysosomal and nonlysosomal sulfatase deficiencies	Brain, liver, spleen, bone	Sulfatide, dermatan sulfate, heparan sulfate
Gangliosidoses
GM₂ gangliosidoses
Infantile Tay-Sach disease (TSD)	Locus: 15q23-q24	Hexosaminidase A (a chain)	Brain	GM₂ ganglioside
Juvenile TSD		Hexosaminidase A (a chain)	Brain	GM₂ ganglioside
Adult TSD		Hexosaminidase A (a chain)	Brain	GM₂ ganglioside
Activator deficiency	Locus: 5q31-q33	GM₂ activator	Brain	GM₂ ganglioside
Sandhoff disease		Hexosaminidase B and A (\| chain)	Brain, liver, spleen, bone	GM₂ ganglioside, globoside
GM₁ gangliosidoses	Locus: 3p21	\|-Galactosidase	Brain, liver, spleen, bone	GMj ganglioside, keratan sulfate
Neutral sphingolipidoses
Fabry disease	Locus: Xq22	a-Galactosidase A	Kidney, vascular endothelial system, heart, central nervous system vessels	Globotriaosylceramide
Schindler disease	Locus: 22q11	a-N-Acetylgalactosaminidase	Brain (probably several variants)	N-Acetylgalactosamine-linked oligosaccharides
Krabbe disease Niemann-Pick disease	Locus: 14q31	Galactocerebrosidase	Brain	Galactocerebroside
(Niemann-Pick A disease [infantile])	Locus: 11p15.4-p15.1	Sphingomyelinase	Brain, liver, spleen, lungs	Sphingomyelin
(Niemann-Pick B disease [late-onset])	Locus: 18q11-q12 (C1)	Sphingomyelinase	Liver, spleen, lungs	Sphingomyelin
(Niemann-Pick C disease)	Locus: 18q11-q12 (C2)
Neutral lipid storage
diseases
Wolman disease	Locus: 10q24-q25	Lysosomal acid lipase	Liver, spleen, adrenal glands, bone marrow	Cholesteryl esters, triglycerides
Cholesterol ester storage disease	Locus: 10q23	Lysosomal acid lipase	Liver, spleen, blood vessels	Cholesteryl esters
Farber disease		Ceramidase	Brain, joints, tendons, skin, liver	Ceramide

Eosinophil Function

Eosinophils respond to a variety of chemotactic factors that enable them to enter tissues and carry out their functions. Some chemokines and chemotactic factors, such as C5a, N-formylme-thionyl-containing peptides, and leukotriene B4, stimulate both eosinophils and neutrophils. Several chemotactic stimuli, however, are highly specific for eosinophils. Among these eosino-phil-specific stimuli are platelet-activating factor (PAF), eosinophil chemotactic factor of anaphylaxis, and a variety of parasite-derived factors. Responses to PAF, one of the most potent activators of normal eosinophils, include chemotaxis, adherence, enhanced binding of IgE, production of superoxide, release of granule proteins, and synthesis of prostanoids.

Both the production and activation of eosinophils are affected by GM-CSF, IL-5, and IL-3. IL-5 appears to be critical for eosinophil production and deployment.63 Exposure to low doses of IL-5 also specifically primes eosinophils for later actions by other stimulants. Once activated, the eosinophils have enhanced generation of reactive oxygen species, enhanced glucose utilization and transport, increased oxygen consumption, a reduced cell surface charge, and activation of acid phosphatases in specific granules.

Eosinophils enhance the immune response to helminths. They perform this function by binding to the surface of both larval and adult forms, by damaging target cells through oxygen-dependent mechanisms that are similar to those of neutrophils, and by damaging cell surfaces by releasing granule proteins such as MBP and ECP. Although the release of these proteins similarly damages normal tissues and tumor cells, these interactions between eosinophils and host cells are less well understood. Eosinophils also produce cytokines that enhance the in flammatory response.64 The presence of eosinophilia in patients with Hodgkin disease appears to be a function of the production of IL-5 by Reed-Sternberg cells. Eosinophils contribute to the fi-brosis of the nodular sclerosis type of Hodgkin disease by producing transforming growth factor-|1.

Disorders of Eosinophil Number

Eosinophilia

Evaluation of the patient with eosinophilia (eosinophil count > 700/mm3) is difficult because the causes of this disorder are multiple and diverse.65 Common causes of secondary eosinophil-ia include allergic disorders, infections caused by parasites and other organisms, dermatologic diseases, pulmonary diseases, collagen vascular disease, neoplasms, and immunodeficiency diseases. There are also myriad uncommon causes, such as eosin-ophilic gastroenteritis, inflammatory bowel disease, chronic active hepatitis, pancreatitis, and hypopituitarism.

Hypereosinophilic Syndrome

The term hypereosinophilic syndrome (HES) is often used for patients with chronic eosinophilia of unknown cause.66 The criteria used to diagnose HES are an unexplained eosinophil count of greater than 1,500/mm3 for longer than 6 months and signs or symptoms of infiltration of eosinophils into tissues. Recent evidence points to a mutation in chromosome 4 that results in linkage of the Rhe gene and the PDGFRa gene.67

The clinical features of HES are rash, fever, cough, dyspnea, diarrhea, and peripheral neuropathy. Patients may have chronic congestive heart failure, valvular abnormalities, and distinctive, fibrous, biventricular endocardial thickening with mural throm-bi.66 The blood smear of a patient with HES usually reveals normal mature eosinophils of typical morphology; however, the presence of hypogranulation and cytoplasmic vacuoles has been reported. The total leukocyte count is typically 10,000 to 30,000/mm3, 30% to 70% of which are eosinophils. The bone marrow is generally hypercellular, with eosinophils constituting 25% to 75% of the marrow elements.

HES can usually be distinguished from malignant disorders associated with eosinophilia, such as acute or chronic eosino-philic leukemias.68 Allergic reactions must also be excluded; the exclusion of such a reaction is usually based on the history, physical examination, and review of current medications. Because many drugs may generate an allergic reaction accompanied by eosinophilia, all nonessential medication should be discontinued before the patient is evaluated.

Parasitic infections, most commonly with such tissue-invasive helminths as filariae and Strongyloides, Trichinella, Schistosoma, and Toxocara species, frequently present with eosinophilia. To eliminate parasitosis as the cause of eosinophilia, multiple stool samples and a small bowel aspirate are recommended, particularly in patients who are at particular risk for infection (e.g., those who frequently travel, those who are exposed to animals, and those who have immunodeficiencies). If these test results are negative, sero-logic assays, radiologic tests, and peripheral blood and bone marrow smears should be performed to exclude the presence of connective tissue diseases, occult lymphoproliferative syndromes and solid tumors, and hematologic malignancies, respectively. In patients with possible cardiac involvement, an echocardiogram should be performed.

Therapy is directed toward lowering the eosinophil count and correcting specific symptoms.

Table 7 Causes of Lymphocytosis

Lymphoproliferative disorders (primary lymphocytosis)

Leukemia

Acute lymphocytic leukemia

Chronic lymphocytic leukemia

Hairy-cell leukemia

Large granular lymphocyte leukemia

Lymphoma

Monoclonal B cell lymphocytosis

Reactive (secondary) lymphocytosis

Viral infection (most likely with EBV, CMV, HIV, HSV, VZV, rubella, adenovirus, or hepatitis virus)

Toxoplasmosis

Pertussis

Stress

Acute

Cardiovascular collapse

Septic shock

Sickle cell crisis

Status epilepticus

Trauma

Surgery

Drugs

Hypersensitivity

Chronic

Autoimmune disorders

Cancer

Hyposplenism

Sarcoidosis

Cigarette smoking

CMV—cytomegalovirus

EBV—Epstein-Barr virus

HSV—herpes simplex virus

VZV—varicella-zoster virus

If symptoms involving the lungs or the heart are present, prednisone at a dosage of 1 mg/kg/day should be given for 2 weeks, followed by 1 mg/kg every other day for 3 months or longer. If this treatment fails or if an alternative is necessary to avoid steroid side effects, hydroxyurea at a dosage of 0.5 to 1.5 g/day should be given to lower the WBC count to less than 10,000/mm3 and the eosinophil count to less than 5,000/mm3. Study findings suggest that treatment with imatinib mesylate is effective.69 Alternative agents include inter-feron alfa, cyclosporine, and etoposide.

Basophil and Mast Cell Physiology

Basophils and mast cells are important in immediate hyper-sensitivity reactions, asthma, urticaria, allergic rhinitis, and ana-phylaxis.70 They are derived from a common hematopoietic progenitor cell in the bone marrow and are stimulated by soluble mediators, primarily IgE, to release granule contents and arachidonic acid metabolites from their plasma membranes.

The cytoplasmic granules of both basophils and mast cells contain sulfated glycosaminoglycans; in normal basophils, the sulfated glycosaminoglycans are predominantly heparin. The sulfated glycosaminoglycans are the granule contents that are primarily responsible for the intense staining of the basophil. Most, if not all, of the circulating histamine in the body is synthesized by the basophil and stored in its granules. Degranulation causes the release of histamine, which mediates many immediate hypersensitivity effects and which, because it is a potent eosinophil chemoattractant, draws eosinophils to the site of de-granulation. Other substances that are released on basophil de-granulation include additional eosinophil chemotactic factors and a variety of arachidonic acid metabolites, the most important of which is leukotriene C4. In addition, the cell membranes of basophils contain high-affinity IgE receptors, the number of which tends to be increased in allergic persons.

Disorders of Basophil Number

Basophilia

Basophilia (basophil count > 150/mm3) is seen in myeloprolif-erative disorders, such as CML, polycythemia vera, and myeloid metaplasia; after splenectomy; in some hemolytic anemias; and in Hodgkin disease. The basophil count can also be increased in patients with ulcerative colitis or varicella infection. Although ba-sophils and mast cells are involved in immediate hypersensitivity reactions and basophils are often seen in areas of contact dermatitis, basophilia is not seen in patients with these disorders.

Lymphocyte Physiology

Lymphocytes (e.g., B cells and T cells) are also derived from hematopoietic stem cells. These cells develop and mature in the bone marrow, thymus, spleen, and lymph nodes and in other specialized lymphoid tissues [see Section 6 Immunology and Allergy].

Disorders of Lymphocytes

Lymphocytosis

Lymphocytosis in adults is defined as an absolute lymphocyte count greater than 4,000/mm3. In children with the disease, lymphocyte counts are higher than in adults and may be as high as 20,000/mm3 in the first year of life. The blood film of any patient with lymphocytosis should be carefully examined to determine the morphology and diversity of the lymphocytes (e.g., reactive lymphocytes, large granular lymphocytes, blasts, or smudge cells).

Lymphocytosis can be either primary or secondary. Primary lymphocytosis, often called lymphoproliferative disease, is caused by dysregulation in the production of lymphocytes. The primary lymphocytoses include the leukemias (e.g., chronic lym-phocytic leukemia, acute lymphocytic leukemia, hairy-cell leukemia, or large granular lymphocyte leukemia), the lym-phomas, and monoclonal B cell lymphocytosis [see Table 7].

The reactive, or secondary, lymphocytoses are conditions that involve absolute increases in lymphocytes caused by physiologic or pathophysiologic responses to infection, inflammation, toxins, cytokines, or unknown agents. The most common causes of reactive lymphocytosis are viral infections: Epstein-Barr virus, cytomegalovirus, herpes simplex virus, varicella-zoster virus, rubella, human T cell lymphotropic virus type I (HTLV-I), HIV, adenovirus, or one of the hepatitis viruses is frequently responsible for the disease. Other pathogens that produce lymphocytosis are Toxoplasma gondii and, in children, Bordetella pertussis (which causes the lymphocyte count to rise to as high as 70,000/mm3). Lymphocytosis is also associated with stress and consequent release of epineph-rine, such as that seen in patients who have had cardiovascular collapse, septic shock, sickle cell crisis, status epilepticus, trauma, major surgery, drug reactions, or hypersensitivity.

Table 8 Causes of Lymphocytopenia

Inherited

Congenital immunodeficiency diseases

Severe combined immunodeficiency

Adenosine deaminase deficiency

Purine-nucleoside phosphorylase deficiency

Reticular dysgenesis

Ataxia-telangiectasia

Wiskott-Aldrich syndrome

Cartilage-hair hypoplasia

Idiopathic CD4⁺ T lymphocytopenia

Acquired

Infection

Viral (e.g., with HIV, a hepatitis virus, influenza virus, or respiratory syncytial virus)

Bacterial (e.g., typhoid fever, pneumonia, sepsis, or tuberculosis)

Aplastic anemia

Autoimmune diseases

Hodgkin disease

Sarcoidosis

Renal failure

Protein-losing enteropathies

Chylous ascites

Zinc deficiency

Chronic alcohol ingestion

Immunosuppressive agents (e.g., antithymocyte globulin, corticosteroids, chemotherapeutic agents, and radiation)

Persistent lymphocytosis may be seen in patients with autoimmune disorders, sarcoidosis, hyposplenism, or cancer and in those who are long-term cigarette smokers.

Lymphocytopenia

Lymphocytopenia is defined as a total lymphocyte count less than 1,000/mm3. Because in adults 80% of lymphocytes are T cells, most cases of lymphocytopenia are caused by a reduction in the T cell count. The mechanisms of lymphocytopenia are often unknown, and the causes are usually differentiated as inherited or acquired.

Inherited lymphocytopenias are usually caused by congenital immunodeficiency diseases. These diseases include severe combined immunodeficiency (e.g., adenosine deaminase deficiency, purine-nucleoside phosphorylase deficiency, and reticular dys-genesis), ataxia-telangiectasia, Wiskott-Aldrich syndrome, and cartilage-hair hypoplasia [see Table 8]. In addition, some persons have idiopathic CD4+ T cell lymphocytopenia.

Acquired lymphocytopenia can be seen in patients with viral infections, such as HIV infection, hepatitis, influenza, and respiratory syncytial virus infection; in patients with certain bacterial infections, such as typhoid fever, pneumonia, sepsis, and tuberculosis; and in patients with aplastic anemia, autoimmune diseases, Hodgkin disease, sarcoidosis, renal failure, protein-losing enteropathies, and chylous ascites. Zinc deficiency and long-term alcohol ingestion are also associated with lymphocytope-nia. Finally, immunosuppressive agents, such as antithymocyte globulin, corticosteroids, chemotherapeutic agents, and radiation, also produce lymphocytopenia.