Cells of Innate Immune System PDF

1 Cells of Innate Immune System DR. SNEHA DOKHALE ASSISTANT PROFESSOR BK BIRLA COLLEGE, KALYAN  Hematopoesis 2  Hematopoiesis  All blood cells arise from a type of cell called the hematopoietic stem cell (HSC).  Stem cells are cells that can differentiate...

1 Cells of Innate Immune System DR. SNEHA DOKHALE ASSISTANT PROFESSOR BK BIRLA COLLEGE, KALYAN  Hematopoesis 2  Hematopoiesis  All blood cells arise from a type of cell called the hematopoietic stem cell (HSC).  Stem cells are cells that can differentiate into other cell types; they are self-renewing—they maintain their population level by cell division.  Hematopoiesis is the formation and development of red and white blood cells 1. In humans, hematopoiesis begins in the embryonic yolk sac during the first weeks of development. 2. Here, yolk-sac stem cells differentiate into primitive erythroid cells that contain embryonic hemoglobin. 3. In the third month of gestation, hematopoietic stem cells migrate from the yolk sac to the fetal liver and then to the spleen; these two organs have major roles in hematopoiesis from the third to the seventh months of gestation. 4. After that, the differentiation of HSCs in the bone marrow becomes the major factor in hematopoiesis, and by birth there is little or no hematopoiesis in the liver and spleen. 3  Hematopoiesis and Cells of the Immune System  Stem cells are defined by two capacities: (1) the ability to regenerate or “self-renew” and (2) the ability to differentiate into diverse cell types.  Embryonic stem cells have the capacity to generate almost every specialized cell type in an organism (in other words, they are pluripotent).  Adult stem cells, in contrast, have the capacity to give rise to the diverse cell types that specify a particular tissue (they are multipotent).  Multiple adult organs harbor stem cells that can give rise to cells specific for that tissue (tissue- specific stem cells).  The HSC was the first tissue-specific stem cell identified and is the source of all of our red blood cells (erythroid cells) and white blood cells (leukocytes). 4  Hematopoietic Stem Cells Differentiate into All Red and White Blood Cells  HSCs originate in fetal tissues and reside primarily in the bone marrow of adult vertebrates.  A small number can be found in the adult spleen and liver.  Regardless of where they reside, HSCs are a rare subset—less than one HSC is present per 5 ×10 cells in the bone marrow.  Their numbers are strictly controlled by a balance of cell division, death, and differentiation.  Their development is tightly regulated by signals they receive in the microenvironments of primary lymphoid organs. 5  Hematopoietic Stem Cells Differentiate into All Red and White Blood Cells  Under conditions when the immune system is not being challenged by a pathogen, most HSCs are quiescent; only a small number divide, generating daughter cells.  Some daughter cells retain the stem-cell characteristics of the mother cell—that is, they remain self-renewing and are able to give rise to all blood cell types.  Other daughter cells differentiate into progenitor cells that have limited self-renewal capacity and become progressively more committed to a particular blood cell lineage.  As an organism ages, the number of HSCs decreases, demonstrating that there are limits to an HSC’s self-renewal potential.  When there is an increased demand for hematopoiesis, for example, during an infection or after chemotherapy, HSCs display an enormous proliferative capacity 6 7  Cells of Immune System  Leukocytes: Cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist.  Lymphocytes: A lymphocyte is a type of white blood cell in the vertebrate immune system. The three major types of lymphocyte are T cells, B cells and natural killer (NK) cells. T cells (thymus cells) and B cells (bursa-derived cells) are the major cellular components of the adaptive immune response. 8  Cells of Immune System 9  Leukocytes  Leukocytes (white blood cells) are immune system cells involved in defending the body against infectious disease and foreign materials.  Five different types of leukocytes exist, all produced and derived from a multipotent cell in the bone marrow known as a hematopoietic stem cell.  The innate leukocytes include the phagocytes, mast cells, eosinophils, basophils, and natural killer cells.  These cells identify and eliminate pathogens and are important mediators in the activation of the adaptive immune system. 10  Leukocytes In practice, leukocytes are divided into two main groups: 1. Granulocytes, those with prominent stainable cytoplasmic granules, and 2. Agranulocytes are those without prominent stainable cytoplasmic granulocytes are mononuclear leukocytes. Neutrophils, Eosinophils, Basophils & Mast Cells are types of granulocytes, whereas Monocytes and lymphocytes are agranulocytes leukocytes. 11 8  Granulocytes  Granulocytes are often the first responders during an immune response and fall into four main categories: neutrophils, eosinophils, basophils, and mast cells.  All granulocytes have multilobed nuclei that make them visually distinctive and easily distinguishable from lymphocytes, whose nuclei are round.  Granulocyte subtypes differ by the staining characteristics of their cytoplasmic granules, membrane-bound vesicles that release their contents in response to pathogens.  These granules contain a variety of proteins with distinct functions: some damage pathogens directly; some regulate trafficking and activity of other white blood cells, including lymphocytes; and some contribute to the remodeling of tissues at the site of infection. 13  Neutrophils  Constitute the majority (50% to 70%) of circulating leukocytes in adult humans and are much more numerous than eosinophils (1%–3%), basophils (