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. 2017 Feb 17:724–804.e2. doi: 10.1016/B978-0-323-35775-3.00013-8

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Copyright © 2017 Elsevier Inc. All rights reserved.

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Figure 13-2 — Classic and Spatial Model of Hematopoietic Cell Differentiation, Canine Blood Smears, and Bone Marrow Aspirate.

The bone marrow consists of (1) hematopoietic stem cells, pluripotent cells capable of self-renewal; (2) progenitor cells that evolve into more differentiated cells with each cell division; (3) precursor cells that can be identified by light microscopy (not shown, see Fig. 13-3); and (4) mature hematopoietic cells awaiting release into the blood vasculature. The earliest lineage commitment is to either the common myeloid progenitor (CMP), which produces platelets, erythrocytes, and nonlymphoid leukocytes, or the common lymphoid progenitor (CLP), which differentiates into various lymphocytes and plasma cells. The cell origin of mast cells is unclear, but they may originate from a stem cell or a myeloid progenitor. Megakaryocytes remain in the bone marrow and release cytoplasmic fragments, or platelets, into blood sinusoids. T lymphocyte progenitor (TLP) cells travel from the bone marrow to the thymus during normal T lymphocyte maturation. During homeostasis, platelets and erythrocytes remain in circulation, but the leukocytes leave blood vessels to enter the tissues, where they actively participate in immune responses. In particular, monocytes and B lymphocytes undergo morphologic and immunologic changes to form macrophages and plasma cells, respectively. Macrophages, granulocytes, and mast cells migrate unidirectionally into tissues, but lymphoid cells can recirculate between the blood, tissues, and lymphatic vessels. BLP, B lymphocyte progenitor; EP, erythroid progenitor; GMP, granulocyte-macrophage progenitor; GP, granulocyte progenitor; MCP, mast cell progenitor; MKP, megakaryocyte progenitor; MEP, megakaryocyte-erythroid progenitor; MP, macrophage progenitor; NK cell, natural killer cell; NKP, natural killer cell progenitor; TLP, T lymphocyte progenitor; TNKP, T lymphocyte–natural killer cell progenitor.

(Courtesy Dr. K.M. Boes, College of Veterinary Medicine, Virginia Polytechnic Institute and State University; and Dr. J.F. Zachary, College of Veterinary Medicine, University of Illinois.)