Myelopoiesis and Lymphopoiesis Amy Lovett-Racke, PhD Associate Professor Department of Microbial Infection and Immunity

Learning Objectives  Know which cells are derived from the three major progenitor cells.  Know which cells play a role in innate versus adaptive immune responses.  Describe the role of cytokines in hematopoiesis.

Hematopoiesis  The generation of the cellular components of blood, including the red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.  Leukocytes – white blood cells; include lymphocytes, granulocytes and monocytes.

Anatomical Site and Rate of Hematopoiesis May Change

Pluripotent Hematopoietic Stem Cell

CD34 – cell surface marker of HSCs CD34

Progenitor Cells

Cytokines Cytokines are proteins made by cells that affect the behavior of other cells.

Erythropoietin (EPO) is a cytokine that promotes the development of erythrocytes. Erythropoietin EPO

Cytokines are proteins made by cells that affect the behavior of other cells. Thrombopoietin (TPO) is the primary cytokine that promotes the development of megakaryocytes. thrombocytes Thrombopoietin TPO

Common Lymphoid and Common Myeloid Progenitor Cells

Innate Immune Cells

GM-CSF – granulocytes macrophage stimulating factor M-CSF – macrophage colony stimulating factor G-CSF – granulocyte colony stimulating factor IL-3 – interleukin-3 Cytokines

B and T Cells Adaptive Immune Cells

NK Cells

Hematopoiesis begins during embryogenesis

Proportion of each immune cell in the peripheral blood various significantly

Summary 1.All blood cells originate from hematopoietic stem cells. 2.Blood cells are divided into three types based on progenitor cell origination; erythroid/megakarocyte (red blood cells and megakaryocytes), myeloid and lymphoid. 3.Myeloid and lymphoid derived cells are the white blood cells and are responsible for innate and adaptive immune functions. 4.Cytokines play a vital role in the development of immune cells. 5.Hematopoiesis occurs predominantly in the bone marrow, but originates in the yolk sac and fetal liver/spleen during development.

Terminology Hematopoiesis - The generation of the cellular components of blood, including the red blood cells (erythrocytes), white blood cells (leukocytes), and platelets. CD (cluster of differentiation) – a system to naming and characterizing cell surface molecules on immune cells. CD34 – a cell surface molecule expressed by hematopoietic stem cells. Cytokines - proteins made by cells that affect the behavior of other cells; cytokines provide a mechanism for different cells to communicate with each other. Erythropoietin (EPO) - a cytokine that promotes the development of erythrocytes (red blood cells). Thrombopoietin (TPO) - the primary cytokine that promotes the development of megakaryocytes.

Terminology Thrombocytes – platelets; derived from megakaryocytes Innate immune cells – cells derived from myeloid progenitors and NK cells; these cells act early in infection and are not specific for the pathogen. Adaptive immune cells – B cells and T cells which differentiate upon infection into cells that recognize the specific pathogen; responses have memory and therefore, can rapidly recognize the same pathogen upon re-infection.

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