L5 Immune System Structure & Function PDF

L5- Structure & Function of Immune system Dr. Janita Pinto September 30, 2020 www.gmu.ac.ae COLLEGE OF  Learning Objectives At the end of this class students should be able to: Explain the...

L5- Structure & Function of Immune system Dr. Janita Pinto September 30, 2020 www.gmu.ac.ae COLLEGE OF  Learning Objectives At the end of this class students should be able to: Explain the organization of lymphoid system; Describe the cells of immune system; List the major lymphoid organs and discuss their functions and Describe characteristics of T & B cells and explain the subsets of T lymphocytes Introduction ⮚ Immune System - Complex network of specialized cells and organs that defend the body against attacks of Foreign invaders ⮚ Immunity is the reaction of the body against any foreign invaders. ⮚ Any substance capable of triggering an Immune Response is called Antigen ⮚ An antigen can be a virus, bacteria, fungus, parasite, portion or product of organism, grafts. Immune System Functions The purposes of the immune system can be broken down into three categories: To defend against pathogens (eg, bacteria, viruses, parasites) To defend against malfunctioning cells (eg, neoplasms) To help “clean up” old tissue to facilitate growth Immune System Organization  Organs of immune system ⮚ Stationed throughout the body; called Lymphoreticular System, comprising Central Bone marrow -Lymphoid Organs Thymus Peripheral Lymph Nodes, Spleen, MALT -Lymphoid Cells T and B (and their secretions) lymphocytes Phagocytes, -Reticuloendothelial Lymphocytes, system cells NK cells, Neutrophils, Eosinophils, Basophils  Central Lymphoid organs- Bone marrow and Thymus ⮚ All cells destined to become immune cells are produced in the Bone marrow. ⮚ The key operatives of Immune system are T and B Lymphocytes ⮚ B lymphocytes stay and complete their maturation in Bone Marrow. ⮚ T lymphocytes migrate from Bone marrow to Thymus. ⮚ They mature, multiply, become immunocompetent (to bear antigen receptors and CD proteins) and learn to distinguish between self and nonself in the thymus.  Organized lymphoid tissue. Haemopoietic stem cells (S) arising in the bone marrow differentiate into common lymphoid progenitor cells and then into immunocompetent B and T cells in the primary lymphoid organs. The T and B cells colonize the secondary lymphoid tissues where immune responses are organized. GALT, Gut-associated lymphoid tissue; MALT, mucosa-associated lymphoid tissue. CELLS OF IMMUNE SYSTEM  Reticuloendothelial cells PHAGOCYTES- large white cells that can engulf and digest antigenic particles. Also have the ability to present antigen to lymphocytes. TYPES OF PHAGOCYTES ⮚ Monocytes/ Macrophages ⮚ Dendritic/ Langerhan cells ⮚ Polymorphonuclear leucocytes, Neutrophils, Eosinophils and Basophils..  Reticuloendothelial cells ⮚ Important phagocytes are monocytes and macrophages. ⮚ Monocytes in blood, Macrophages in tissues. ⮚ Specialized macrophages include alveolar macrophages in the lungs, mesangial phagocytes in the kidneys, microglial cells in the brain, and Kupffer cells in the liver. FUNCTIONS-Apart from scavenging/ phagocytosis, they are foremost among the cells that "present" antigen to T cells, having first digested and processed it, macrophages play a crucial role in initiating the immune response. ⮚ Other Antigen Presenting cells - B lymphocytes, Dendritic and Langerhan cells. The mononuclear phagocyte system  Lymphocytes and secretions ⮚ Lymphocytes are present in blood, lymph, lymphoid organs and tissues. ⮚ Types of lymphocytes (based on presence or absence of Special “Surface Markers”) -B lymphocytes -T lymphocytes -NK ( Natural Killer ) Cells ⮚ Secretions of T and B lymphocytes and macrophages are called- Cytokines/Interleukins ⮚ Also called- Lymphokine, Interleukin, Monokine (by Monocytes) ⮚ They play a major role in the inflammatory response. ⮚ They encourage cell growth, promote cell activation, destroy target cells, and incite macrophages.  Antigen Receptors ⮚T cell -T CELL RECEPTOR - CD proteins ⮚ B cells - B CELL RECEPTOR (monomeric Ig M)  T lymphocytes Lymphocyte subsets are distinguished by distinctive molecules on cell surface called CD markers. In addition to CD markers, T cells have different kinds of antigen recognition units- Y shaped- either alpha/beta or gamma/delta- called TCR (T cell Receptors). The 2 main subsets of T lymphocytes are Helper T cells (T4 or CD4)- essential in activating B cells, other T cells, NK cells and Macrophages Cytotoxic T cells (T8 or CD8)- directly attack body cells that are infected or malignant The other subsets of T lymphocytes include Suppressor T cells Memory T Cells FUNCTIONs Helper T cells are vital to orchestrating the immune system.(They are essential in activating B cells, other T cells, NK cells and macrophages). Cytotoxic T cells directly attack body cells that are infected (with viruses) or malignant cells. They are also responsible for graft rejection. Suppressor T cells “turn off” or suppress the activated T cells. Memory T cell help in a quick response on subsequent stimulus with same antigen.  B lymphocyte ⮚ When a B cell encounters its triggering antigen(along with collaborating T cells and accessory cells), it gives rise to many large plasma cells. ⮚ Every plasma cell is essentially a factory for producing specific antibody. It manufactures millions of identical antibody molecules and pours them into the bloodstream. ⮚ Antibody interlocks with the antigen and thereby marks it for destruction. ⮚ Some plasma cells also become memory cells. Functions 1.Differentiating into plasma cells & secrete antibodies 2. Antigen presentation  Natural Killer cells ⮚ 10% of lymphocytes ⮚ Unlike cytotoxic T cells, do not need to recognize a specific antigen before killing the cell. ⮚ They target tumor cells and protect body against a wide variety of infectious microbes.  Complement (C) A system of serum proteins that have the ability to complement (augment) the effects of other components of immune system (eg. Antibody). Important component of innate immunity. Innate Immunity Adaptive immunity References Text Book Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 8th ed. Elsevier Ltd; 2015. ISBN 13: 978-0-323-29956-5. https://www.clinicalkey.com/#!/browse/book/3-s2.0-C2013019575X?indexOverrid e=GLOBAL Recommended Readings: Goering RV, Dockrell HM, Zuckerman M, Chiodini PL. Mims' Medical Microbiology and Immunology, 6th ed. Elsevier Ltd; 2019. ISBN: 9780702071546. https://www.clinicalkey.com/#!/content/book/3-s2.0-B9780702071546000096?ind exOverride=GLOBAL Levinson W. Review of Medical Microbiology and Immunology, 13th Edition. US: McGraw Hill; 2014. ISBN-13: 978-007-1818-117. Chapters 6-8, 57-61, 63, PP. 26-60, 475-520, 527-530.