Chapter 33: Basophils, Mast Cells, and Related Disorders

BASOPHILS

• The basophil is the least common granulocyte.

• Normal basophil count is 0.015 to 0.08 × 10⁹/L.

• The causes of basopenia (decreased numbers) and basophilia (increased numbers) are listed in Table 33–1.

BASOPENIA

• Hereditary absence of basophils is very rare.

• Other causes include high doses of glucocorticoids, hyperthyroidism or therapy with thyroid hormones, ovulation, hypersensitivity reactions, or leukocytosis in association with diverse disorders.

BASOPHILIA

• Causes include allergy or inflammation, endocrinopathies (diabetes mellitus, hypothyroidism), infections, iron deficiency, exposure to ionizing radiation, and neoplasias.

• Basophilia occurs in virtually all patients with chronic myelogenous leukemia (CML).

• De novo acute basophilic leukemia is very rare, but marrow basophilia may be associated uncommonly with other subtypes of acute myelogenous or acute promyelocytic leukemia.

• Basophils in acute or chronic clonal myeloid diseases are derived from the malignant clone and occasionally may cause symptoms of histamine release (flushing, pruritus, hypotension) or severe peptic ulcer disease reflecting hypersecretion of gastric acid and pepsin.

MAST CELLS AND SECONDARY CHANGES IN NUMBERS

• Mast cells are produced in the marrow and then transit the blood to the tissues where they reside. They cannot be identified in transit in the blood of healthy individuals by standard techniques.

• Mast cells contain mediators that may be preformed in granules (eg, histamine, heparin, and chemotactic factors) or newly formed (eg, arachidonic acid metabolites, such as prostaglandin D₂ and leukotrienes).

• An increased number of mast cells may be seen in tissues of immunoglobulin E–associated disorders, connective tissue disorders, at infection sites, and in the lymph nodes and marrow in a variety of benign and malignant tumors (see Table 33–2).