Immunology Chapter 1 PDF

Immunology 2nd Year / 1st Semester Chapter 1 Overview of the Immune System Dr. Lina ISMAIIL 2024-2025  Chapter 1 Plan 1- Overview of the immune system (IS)  Definition of IS...

Immunology 2nd Year / 1st Semester Chapter 1 Overview of the Immune System Dr. Lina ISMAIIL 2024-2025  Chapter 1 Plan 1- Overview of the immune system (IS)  Definition of IS  The organs of the immune system  The main natural lines of defense 2- Components of immunity  Innate immunity  Acquired immunity 3- Humoral and cell-mediated response 4- Maturation and clonal selection of B lymphocytes 5- Specificity and memory: Primary and secondary immune responses 6- Immune dysfunction and its consequences Immunology / 2024-2025  Chapter 1 1- Overview of the immune system (IS) Immunity: set of humoral and cellular factors, specific or not, for the foreign substance introduced and which protects the body from external attacks. The immune system (IS): is a defense system composed of organs, cells and very varied molecules, capable of recognizing and eliminating a large number of foreign elements. Immunology / 2024-2025  Chapter 1 The Immune System has two functions: 1- Specific recognition function. 2- Function of regenerating effector responses and memories (conversion of initial recognition into effector responses) Immunology / 2024-2025  Chapter 1 The organs of the immune system Immunology / 2024-2025  Chapter 1 The organs of the immune system The thymus and bone marrow are the primary (or central) lymphoid organs, where maturation of lymphocytes takes place. The lymph nodes, spleen, and various mucosal- associated lymphoid tissues (MALT) such as gut- associated lymphoid tissue (GALT) are the secondary (or peripheral) lymphoid organs, which trap antigen and provide sites for mature lymphocytes to interact with that antigen. In addition, tertiary lymphoid tissues, which normally contain fewer lymphoid cells than secondary lymphoid organs, can import lymphoid cells during an inflammatory response. Immunology / 2024-2025  Chapter 1 The 3 lines of defense 1. First line  Skin,  Mucous membrane (physical barrier) Non specific defense OR 2. Second line  Antimicrobial proteins (interferons, complement Innate immunity  Phagocytes (neutrophils, macrophages)  Inflammatory reaction 3. Third line Specific defense  Immune system (humoral and cellular response) OR Acquired immunity Immunology / 2024-2025  Chapter 1 Natural Immunity It is a set of resistance mechanisms against diseases that are not specific to a particular pathogen Provides the first line of defense after host exposure to a pathogen Made up of four types of defensive barriers: 1- Anatomical (the skin, The mucous membrane 2- Physiological 3- Phagocytic 4- Inflammatory Immunology / 2024-2025  Chapter 1 Anatomical barrier 1. The skin The sebaceous glands in the dermis produce an oily secretion called sebum. Immunology / 2024-2025  Chapter 1 Anatomical barrier 2. The mucous membrane: Tears, saliva and mucous secretions Mucus coats microorganisms The cilia expel the microorganisms in the mucus The intestinal flora Immunology / 2024-2025  Chapter 1 Physiological barrier Body temperature: inhibits the growth of pathogens PH stomach acid (newborn) Soluble factors Immunology / 2024-2025  Chapter 1 Phagocytic barrier Other natural defense mechanism  Phagocytosis: ingestion of extracellular material Provided by specialized cells (monocytes – neutrophils and macrophages) Immunology / 2024-2025  Chapter 1 Inflammatory barrier Immunology / 2024-2025  Chapter 1 Summary on Non-Specific Host Response Immunology / 2024-2025  Chapter 1 2- Components of immunity  Innate immunity Phagocytic cells consist of: 1- granulocytes (i.e., neutrophils, eosinophils, basophils, and mast cells). 2- monocytes/macrophages, and dendritic cells. These cells participate in not only the phagocytosis but also the inflammatory process. Immunology / 2024-2025  Chapter 1  Innate immunity Complement it is a set of proteins (30) which exist in the plasma in an inactive state which are activated in a highly regulated cascade  Lysis of foreign cells  Facilitation of phagocytosis (opsonization)  Attraction of phagocytes (chemotaxis)  Control of the inflammatory reaction Immunology / 2024-2025  Chapter 1  Acquired immunity Cells: T lymphocytes: responsible for cell- mediated immunity. B lymphocytes: responsible for humoral- mediated immunity and producers of immunoglobulins (Ig). Immunology / 2024-2025  Chapter 1 B lymphocytes (BL) Are produced in the bone marrow by the process of hematopoiesis Maturation occurs in the bone marrow BL expresses an antigen-specific binding receptor (BCR) Binding of Antigen to antibody proliferation and differentiation of Ab-secreting BL plasma cells and memory B cells Immunology / 2024-2025  Chapter 1 T lymphocytes Are produced in the bone marrow by the process of hematopoiesis Maturation occurs in the thymus Expressing a receptor specific for Ag TCR Recognition of Ag linked to molecules of the major histocompatibility complex Immunology / 2024-2025  Chapter 1 Role of MHC in Ag recognition by T cells Two subpopulations of T cells TH helper T cells (Helper CD4) Cytotoxic T cells TC (cytotoxic CD8) Class I MHC molecules are expressed on nearly all nucleated cells. Class II MHC molecules are expressed only on antigen-presenting cells. T cells that recognize only antigenic peptides displayed with a class II MHC molecule generally function as T helper (TH) cells. T cells that recognize only antigenic peptides displayed with a class I MHC molecule generally function as T cytotoxic (TC) cells. Immunology / 2024-2025  Chapter 1 Characteristics of innate immunity and acquired immunity Immunology / 2024-2025  Chapter 1 3- Humoral and cell-mediated response In the humoral response, B cells interact with antigen and then differentiate into antibody secreting plasma cells. The secreted antibody binds to the antigen and facilitates its clearance from the body. In the cell-mediated response, various subpopulations of T cells recognize antigen presented on self-cells. TH cells respond to antigen by producing cytokines. TC cells respond to antigen by developing into cytotoxic T lymphocytes (CTLs), which mediate killing of altered self-cells (e.g., virus-infected cells). Immunology / 2024-2025  Chapter 1 4- Maturation and clonal selection of B lymphocytes Immunology / 2024-2025  Chapter 1 4- Maturation and clonal selection of B lymphocytes Maturation, which occurs in the absence of antigen, produces antigenically committed B cells, each of which expresses antibody with a single antigenic specificity (indicated by 1, 2, 3, and 4). Clonal selection occurs when an antigen binds to a B cell whose membrane bound antibody molecules are specific for epitopes on that antigen. Clonal expansion of an antigen-activated B cell leads to a clone of memory B cells and effector B cells, called plasma cells; all cells in the expanded clone are specific for the original antigen. The plasma cells secrete antibody reactive with the activating antigen. Similar processes take place in the T-lymphocyte population, resulting in clones of memory T cells and effector T cells; the latter include activated TH cells, which secrete cytokines, and cytotoxic T lymphocytes (CTLs). Immunology / 2024-2025  Chapter 1 5. Specificity and memory: Primary and secondary immune responses When an animal is injected with an antigen, it produces a primary serum antibody response of low magnitude and short duration, peaking at about 10–17 days. It is seen at the first contact with Ag, characterized by the production of plasma cells (IgM) and memory cells. takes place in 3 phases: latency, growth and decay phase. Low amplitude and short duration response Immunology / 2024-2025  Chapter 1 5. Specificity and memory: Primary and secondary immune responses A second immunization with the same antigen results in a secondary response that is greater in magnitude, peaks in less time (2–7 days), and lasts longer (months to years) than the primary response. Compare the secondary response to antigen A with the primary response to antigen B administered to the same mice: Memory cells are responsible for the IIary response to the 2nd contact with Ag. There is no lag phase. The response is faster and more intense. The majority of Abs are IgG Immunology / 2024-2025  Chapter 1 6- Immune dysfunction and its consequences Sometimes the immune system fails to protect the host adequately or misdirects its activities to cause discomfort, debilitating disease, or even death. There are several common manifestations of immune dysfunction: Allergy and asthma Graft rejection and graft-versus-host disease Autoimmune disease Immunodeficiency Immunology / 2024-2025  Chapter 1 Hypersensitivity or allergy Sequence of events leading to an allergic response. When the antibody produced upon contact with an allergen is IgE, this class of antibody reacts via its constant region with a mast cell. Immunology / 2024-2025  Chapter 1 Hypersensitivity or allergy Subsequent reaction of the antibody binding site with the allergen triggers the mast cell to which the IgE is bound to secrete molecules that cause the allergic symptoms. Immunology / 2024-2025  Chapter 1 Autoimmune diseases Sometimes the immune system malfunctions and a breakdown in self-tolerance occurs. This could be caused by a sudden inability to distinguish between self and nonself or by a misinterpretation of a self-component as dangerous, causing an immune attack on host tissues.  Multiple sclerosis: immune attack of the brain and central nervous system  Rheumatoid arthritis attacks the joints of the arms and legs Immunology / 2024-2025  Chapter 1 Immunodeficiency  Due to a defect in one or more IS components  Primary immunodeficiency due to a genetic or developmental abnormality (thymus)  Secondary immunodeficiency due to x-rays, immunosuppressants, HIV infection  Example of immunodeficiency: Acquired immunodeficiency syndrome or AIDS Result of infection by a retrovirus (HIV) Characterized by auxiliary TCD4 loss Collapse of the immune system Immunology / 2024-2025