Cellular Components of the Immune System Lecture Notes PDF

The Cellular Components of the Immune system Asst. Prof. Sheila M. Nuraddin Clinical analysis Department College of Pharmacy Hawler Medical University Lec:2 The immune system is made up of organs, networks of cells, and proteins and is scattered throughout the body. The mechanism of action of the im...

The Cellular Components of the Immune system Asst. Prof. Sheila M. Nuraddin Clinical analysis Department College of Pharmacy Hawler Medical University Lec:2 The immune system is made up of organs, networks of cells, and proteins and is scattered throughout the body. The mechanism of action of the immune system is: To create protective barriers to prevent antigens and bacteria from entering the body. When pathogens break through the barrier, white blood cells and proteins are produced and attacked before they have a chance to attack the body. Fight and break-down the invaders. Storing information will help the immune system quickly recognize pathogens if there are future attacks and can fight to protect the body more quickly. The immune system consists of: Organs Cells Molecules 1- Organs Immune System Organs. The key primary lymphoid organs of the immune system include the thymus and bone marrow. The secondary lymphatic tissues including spleen, tonsils, lymph vessels, lymph nodes, adenoids, skin, and liver. The spleen is a blood-filtering organ that removes microbes and destroys old or damaged red blood cells. It also makes disease-fighting components of the immune system (including antibodies and lymphocytes). Bone marrow is the spongy tissue found inside your bones. It produces the red blood cells our bodies need to carry oxygen, the white blood cells we use to fight infection, and the platelets we need to help our blood clot. The thymus filters and monitors your blood content. It produces the white blood cells called T-lymphocytes. In addition, mucosal associated lymphoid tissues (MALTs) and gut associated lymphoid tissues (GALTs) play a vital role in the immune system, although they are considered to be part of the lymphatic system. MALTs are lymphoid tissues found in parts of the body where mucosa is present, such as the intestines, eyes, nose, skin and mouth. They contain lymphocytes and macrophages that defend against pathogens attempting to enter from outside the body. GALTs are lymphoid tissues found in the mucosa and submucosa of the gastrointestinal tract, tonsils, appendix and Peyer’s patches in the small intestine. 2-Cells Component Antigen presenting cell (APC) General Description Cells, such as macrophages, dendritic cells and B cells, that can process antigens protein into peptides. These peptides can then be presented (along with major histocompatibility complex MHC) to Tcell receptors on the surface of the cell. The major histocompatibility complex (MHC) is a group of genes that encode proteins on the cell surface that have an important role in immune response (adaptive immunity). Helper T cell Component General Description Basophil A basophil is a type of phagocytic immune cell that has granules. Inflammation causes basophils to release histamine during allergic reactions. B lymphocyte A B lymphocyte is a type of white blood cell that develops in the bone marrow and makes antibodies. Memory B cell B cells that are long lived and remember past antigen exposure. Plasma B cell Activated B cells that produce antibodies. Only one type of antibody is produced per plasma B cell. Dendritic cell Dendritic cells are antigen-presenting cells (APCs). Antigen is combined with major histocompatibility complex (MHC) and presented on a dendritic cell to active T and B lymphocytes. Eosinophil An eosinophil is a type of immune cell (leukocyte, or white blood cell). They help fight infection or cause inflammation. Granulocyte Granulocytes (including eosinophils, neutrophils and basophils) are a type of white blood cell that releases toxic materials, such as antimicrobial agents, enzymes, nitrogen oxides and other proteins, during an attack from a pathogen. Natural killer (NK) cell The primary effector cell of innate immunity; the first responders of the immune system. They interact with signals from other cells (activating and inhibitory). T lymphocyte Type of white blood cell that is involved with the (also called T immune system. cell) T lymphocytes mature in the thymus and differentiate into cytotoxic, memory, helper and regulatory T cells. Cytotoxic T cell Cytotoxic T cells are the primary effector cells of adaptive immunity. Activated cytotoxic T cells can migrate through blood vessel walls and non-lymphoid tissues. Cytotoxic T cells are activated by cytokines. They can attach to cancer cells and kill them. Memory T cell Derived from activated cytotoxic T cells, memory T cells are long-lived and antigen-experienced. One memory T cell can produce multiple cytotoxic T cells. After activated cytotoxic T cells attack the pathogen, the memory T cells hang around to reduce any recurrence. Helper T cell Helper T cells secrete cytokines that help B cells differentiate into plasma cells. These cells also help to activate cytotoxic T cells and macrophages. Regulatory T Regulatory T cells ( Tregs) help to suppress the cell immune response. Macrophage Macrophages are large white blood cells that reside in tissues that specialize in engulfing and digesting cellular debris, pathogens and other foreign substances in the body. Mast cell Mast cells release histamine and help to get rid of allergens. Monocyte Large white blood cells that reside in the blood stream that specialize in engulfing and digesting cellular debris, pathogens and other foreign substances in the body. Monocytes become macrophages. Neutrophil A type of white blood cell, granulocyte, and phagocyte that aids in fighting infection. Neutrophils kill pathogens by ingesting them. Phagocytes Phagocytes eat up pathogens by attaching to and wrapping around the pathogen to engulf it. Once the pathogen is trapped inside the phagocyte, it is in a compartment called a phagosome. The phagosome will then merge with a lysosome or granule to form a phagolysosome, where the pathogen is killed by toxic materials, such as antimicrobial agents, enzymes, nitrogen oxides or other proteins. 3- Molecules of the immune system A/ Immunoglobulins Immunoglobulins, also known as antibodies, are glycoprotein molecules produced by plasma cells (white blood cells). They act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses, and aiding in their destruction. The various antibodies produced by plasma cells are classified by isotype, each of which differs in function and antigen responses primarily due to structure variability. Five major antibody classes have been identified in placental mammals: IgA, IgD, IgE, IgG and IgM. This classification is based on differences in amino acid sequence in the constant region (Fc) of the antibody heavy chains. Plasma cell producing antibody The five primary classes of immunoglobulins are IgG, IgM, IgA, IgD and IgE. These are distinguished by the type of heavy chain found in the molecule. IgG molecules have heavy chains known as gamma-chains; IgMs have mu-chains; IgAs have alpha-chains; IgEs have epsilon-chains; and IgDs have delta-chains. Antibody structure Antibody classes differ in valency as a result of different numbers of Y-like units (monomers) that join to form the complete protein. For example, in humans, functioning IgM antibodies have five Y-shaped units (pentamer) containing a total of 10 light chains, 10 heavy chains and 10 antigen-binding. Class Switching Sometimes one antibody isotype switches into another following the activation of B-cells. This lets the cell produce different types of antibodies. Initially, B cells express only IgM and IgD on their cell surface. Activating the cell helps it identify the best type of antibody for eliminating the antigen. So, daughter cells from the B cell produce different antibody isotypes (IgG, IgA, or IgE). During class switching, only the constant region of the antibody heavy chain changes. The variable regions, which are the antigen binding sites, do not change. Cytokines trigger class switching. B/ Cytokines (SY-toh-kine) A type of protein that is made by certain immune and non-immune cells and has an effect on the immune system. Some cytokines stimulate the immune system and others slow it down. They can also be made in the laboratory and used to help the body fight cancer, infections, and other diseases. Cytokines are small proteins that are crucial in controlling the growth and activity of other immune system cells and blood cells. When released, they signal the immune system to do its job. Cytokines affect the growth of all blood cells and other cells that help the body's immune and inflammation responses. Cytokine is a general name; other names include lymphokine (cytokines made by lymphocytes), monokine (cytokines made by monocytes), chemokine (cytokines with chemotactic activities), and interleukin (cytokines made by one leukocyte and acting on other leukocytes). Cytokines may act on the cells that secrete them (autocrine action), on nearby cells (paracrine action), or in some instances on distant cells (endocrine action). Figure, (a) Expression of cytokines and their receptors is highly regulated; (b) Cytokines can act in Autocrine (same cell), Paracrine (close proximity) and Endocrine (long distance) ways C/ The complement system The complement system is part of your body's immune system that cleans up damaged cells, helps your body heal after an injury or an infection and destroys microscopic organisms like bacteria that make you sick. Your complement system is the front line of defense for your immune system. At the basic level the broad functions of the complement system can be split into three areas: (1) the activation of inflammation; (2) the opsonization (labeling) of (pathogens and cells ) for clearance/destruction. (3) the direct killing of target cells/microbes by lysis. Components of Complement System: The complement system is made up of a number (more than 20) of distinct serum (blood plasma) and membrane proteins which mostly assist the humoral branch of the immune system. As after initial activation, the various complement components interact sequentially to generate reaction products that facilitate antigen clearance and inflammatory response. The proteins and glycoproteins composing the complement system are synthesized largely by liver hepatocytes, some by blood monocytes, tissue macrophages and epithelial cells of the gastrointestinal and genitourinary tracts. The proteins that form the complement system are labelled numerically with the prefix C (e.g., C1 –C9). Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the lectin pathway. Membrane attack complex MAC Any questions? …………..