Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + INTRODUCTION Download Section PDF Listen +++ ++ 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. + NORMAL BLOOD MONOCYTE CONCENTRATION Download Section PDF Listen +++ ++ 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. + HEMATOLOGIC DISORDERS ASSOCIATED WITH MONOCYTOSIS Download Section PDF Listen +++ ++ See Table 36–1. ++Table Graphic Jump LocationTABLE 36–1DISORDERS ASSOCIATED WITH MONOCYTOSISView Table||Download (.pdf) TABLE 36–1 DISORDERS ASSOCIATED WITH MONOCYTOSIS Hematologic disorders Myeloid neoplasms Myelodysplastic states Acute monocytic leukemia Acute myelomonocytic leukemia Acute monocytic leukemia with histiocytic features Acute myeloid dendritic cell leukemia Chronic myelomonocytic leukemia Juvenile myelomonocytic leukemia B. Infections Chronic myelogenous leukemia (m-BCR–positive type) Polycythemia vera Chronic neutropenias Drug-induced neutropenia Postagranulocytic recovery Lymphocytic neoplasms B-cell Lymphoma T-cell Lymphoma Hodgkin disease Myeloma Macroglobulinemia Drug-induced pseudolymphoma Immune hemolytic anemia Idiopathic thrombocytopenic purpura Postsplenectomy state Inflammatory and Immune Disorders Connective tissue diseases Rheumatoid arthritis Systemic lupus erythematosus Temporal arteritis Myositis Polyarteritis nodosa Sarcoidosis Infections Mycobacterial infections Subacute bacterial endocarditis Brucellosis Dengue hemorrhagic fever Resolution phase of acute bacterial infections Syphilis Cytomegalovirus infection Varicella-zoster virus Gastrointestinal disorders Alcoholic liver disease Inflammatory bowel disease Sprue Nonhematopoietic malignancies Exogenous cytokine administration Myocardial infarction Cardiac bypass surgery Miscellaneous conditions Tetrachloroethane poisoning Parturition Glucocorticoid administration Depression Thermal injury Marathon running Holoprosencephaly Kawasaki disease Wiskott-Aldrich syndrome Source: Williams Hematology, 8th ed, Chap. 71, Table 71–1, p. 1042. +++ 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. + INFLAMMATORY AND IMMUNE DISORDERS ASSOCIATED WITH MONOCYTOSIS Download Section PDF Listen +++ ++ 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). + NONHEMATOPOIETIC MALIGNANCIES Download Section PDF Listen +++ ++ Found in about 20 percent of patients who have monocytosis; independent of metastatic disease. + MISCELLANEOUS CONDITIONS ASSOCIATED WITH MONOCYTOSIS Download Section PDF Listen +++ ++ Alcoholic liver disease. Tetrachloroethane poisoning. Langerhans cell histiocytosis. Parturition. Severe depression. See also Table 36–1. + DISORDERS ASSOCIATED WITH MONOCYTOPENIA Download Section PDF Listen +++ ++ 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. ++ For a more detailed discussion, see Marshall A. Lichtman: Monocytosis and Monocytopenia. Chapter 71, p. 1041 in Williams Hematology, 8th ed.