Chapter 36: Monocytosis and Monocytopenia

• Monocytes in the blood are in transit. They function in the tissues, where they mature into macrophages and participate in:

  • — Inflammation, including granulomatous reactions, atheroma formation, and tissue repair.

  • — Immunologic reactions, including delayed hypersensitivity.

  • — Reactions to neoplasia and allografts.

• The need for macrophages in tissues also can be met by local proliferation of macrophages, not requiring increased transit of blood monocytes.

• Ninety percent of blood monocytes intensely express CD14 (lipopolysaccharide receptor) but not CD16 and 10 percent have weak expression of CD14 and strongly express CD16.

• Older persons have a striking decrease in the proportion of CD14+CD16– to CD14+CD16+ monocytes compared with younger persons.

• Disorders rarely produce abnormalities of monocytes alone in the absence of other blood cell abnormalities.

• The monocyte count averages 1.0 × 10⁹/L in neonatal life, gradually decreasing to a mean of 0.4 × 10⁹/L in adult life.

• Monocytosis (in adults): >0.8 × 10⁹/L.

• Monocytopenia: <0.2 × 10⁹/L.

• See Table 36–1.

Neoplastic or Clonal Monocytic Proliferations

• Oligoblastic myelogenous leukemia (refractory leukemia with excess blasts or myelodysplastic syndrome).

• Acute myelogenous leukemia (myelomonocytic or monocytic types).

• Chronic myelomonocytic leukemia.

• Juvenile myelomonocytic leukemia

• Unusual type of BCR-ABL (p190)-positive chronic myelogenous leukemia with monocytosis.

Reactive (Nonclonal) Monocytic Proliferations

• Neutropenic states: cyclic neutropenia; chronic granulocytopenia of childhood; familial benign neutropenia; infantile genetic agranulocytosis; chronic hypoplastic neutropenia.

• Drug-induced agranulocytosis (transient monocytosis, especially in the recovery phase).

• Chlorpromazine toxicity, monocytosis precedes the agranulocytosis.

• Lymphoma.

• Hodgkin lymphoma.

• Postsplenectomy state.

• Myeloma.

• See Table 36–1.

Collagen Vascular Diseases

• Rheumatoid arthritis.

• Systemic lupus erythematosus.

• Temporal arteritis.

• Myositis.

• Polyarteritis nodosa.

Chronic Infections

• Bacterial infections, e.g., subacute bacterial endocarditis, tonsillitis, dental infections, recurrent liver abscesses (probably not in typhoid fever or brucellosis).

• Tuberculosis.

• Syphilis: neonatal, primary, and secondary.

• Viral infections: cytomegalovirus, varicella-zoster virus.

Other Inflammatory Disorders

• Sprue.

• Ulcerative colitis.

• Regional enteritis.

• Sarcoidosis (the degree of monocytosis is inversely related to reduction in number of T lymphocytes).

• Found in about 20 percent of patients who have monocytosis; independent of metastatic disease.

• Alcoholic liver disease.

• Tetrachloroethane poisoning.

• Langerhans cell histiocytosis.

• Parturition.

• Severe depression.

• See also Table 36–1.

• Aplastic anemia.

• Hairy cell leukemia:

  • — May be a helpful diagnostic clue.

  • — Contributes to the frequent infections.

• Chronic lymphocytic leukemia.

• Cyclic neutropenia.

• Severe thermal injury.

• Rheumatoid arthritis.

• Systemic lupus erythematosus.

• HIV infections.

• Postradiation therapy.

• Following the administration of:

  • — Glucocorticoids.

  • — α-Interferon.

  • — Tumor necrosis factor-α.

Blood Dendritic Cells

• Blood dendritic cells are composed of two phenotypic subtypes: myeloid-derived (HLA-Dr+CD11c+CD123+) and lymphoid-plasmacytoid-derived (HLA-Dr+CD11c–CD123+).

• The total blood dendritic cell count can be measured by flow cytometry.

• Dendritic cells make up approximately 0.6 percent of blood cells (range: 0.15 to 1.30%) and represent 14 × 10⁶ cells/L (range: 3 to 30 × 10⁶ cells/L). Approximately one-third of these cells are lymphoid-plasmacytoid–derived type and two-thirds are myeloid-derived type.

• Blood dendritic cell counts decrease with aging and increase with surgical stress (and presumably other stressful reactions) in relation to plasma cortisol levels.

• Fluctuations in blood dendritic cells are often independent of changes in blood monocyte counts.