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The Immune System (Innate Immunity (Physical Barriers (Skin, Mucous…

- - - - Neutrophils
        
        Neutrophils are white blood cells that play some very important roles in our innate immune system. They circulate around our body in the bloodstream, and when they sense signals that an infection is present, they are the first cells to migrate to the site of the infection to begin killing the invading microbes.
        
        The bone marrow of a normal adult produces about 100 billion neutrophils daily. It takes about one week to form a mature neutrophil from a precursor cell in the marrow; yet, once in the blood, the mature cells live only a few hours or perhaps a little longer after migrating to the tissues.
        
        Neutrophils, the most common type of white blood cell in the bloodstream, are among the first immune cells to defend against infection. They ingest bacteria and other foreign cells. Neutrophils contain granules that release enzymes to help kill and digest these cells.
      - Macrophages
        
        The macrophage is a large white blood cell that is an integral part of our immune system. Its job is to locate microscopic foreign bodies and 'eat' them. Macrophages use the process of phagocytosis to engulf particles and then digest them.
        
        Macrophages are versatile cells that play many roles. As scavengers, they rid the body of worn-out cells and other debris. Along with dendritic cells, they are foremost among the cells that present antigens, a crucial role in initiating an immune response.
        
        The term "macrophage" conjures images of a hungry white blood cell gobbling invading bacteria. However, macrophages do much more than that: Not only do they act as antimicrobial warriors, they also play critical roles in immune regulation and wound-healing
        
        A macrophage is a large, phagocytic cell that engulfs foreign particles and pathogens. Macrophages recognize PAMPs via complementary pattern recognition receptors (PRRs). PRRs are molecules on macrophages and dendritic cells which are in contact with the external environment and can thus recognize PAMPs when present.
      - Basophils
        
        Basophils appear in many specific kinds of inflammatory reactions, particularly those that cause allergic symptoms. Basophils contain anticoagulant heparin, which prevents blood from clotting too quickly. They also contain the vasodilator histamine, which promotes blood flow to tissues.
        
        A granulocyte found in tissue. The contents of mast cells, along with those of basophils, are responsible for the symptoms of allergy. A type of immune cell that is made in the bone marrow and travels through the blood to tissues in the body where it becomes a macrophage.
        
        Mast cells and basophils are the major cells in the early phases of immediate hypersensitivity reactions. Mast cells are fixed in the tissues while basophils circulate in the blood. Both are derived from CD34+ bone marrow progenitor cells.
      - Eosinohphils
        
        The functions of the eosinophil are varied, some of which are very similar to other white blood cells. They are implicated in numerous inflammatory processes, especially allergic disorders. In addition, eosinophils may have a physiological role in organ formation (e. g. postgestational mammary gland development).
        
        Eosinophils may modulate immediate hypersensitivity reactions by degrading or inactivating mediators released by mast cells, such as histamine, leukotrienes (which may cause vasoconstriction and bronchoconstriction), lysophospholipids, and heparin
        
        Red blood cells surround the eosinophil, two platelets at the top left corner. Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates.
      - Natural Killer Cells
        
        Explained in T Cells: Natural Killer T Cells
- - - - Memory Cells
        
        Memory B cells are a B cell sub-type that are formed within germinal centers following primary infection and are important in generating an accelerated and more robust antibody-mediated immune response in the case of re-infection (also known as a secondary immune response).
        
        When these cells encounter the same antigen again they differentiate into antibody-producing plasma cells at a faster and more vigorous rate.
        
        Store the memory of the antibody created to provide future immunity.
        
        Vaccinations
      - Plasma Cells
        
        Plasma cells, also called plasma B cells, plasmocytes, plasmacytes, or effector B cells, are white blood cells that secrete large volumes of antibodies. They are transported by the blood plasma and the lymphatic system.
        
        The first activation signal occurs upon antigen binding to B cell receptors (BCRs). Upon binding to the BCR, the antigen is internalized by receptor-mediated endocytosis, digested, and complexed with MHC II molecules on the B cell surface.
        
        About 70% of the plasma cells in the bone marrow had stopped proliferating within about 3 weeks after immunization and survived for at least another 3 months, without further proliferation, but continuously secreting antibodies.
      - Antibodies
        
        Antibodies function in three distinct ways. They bind directly to antigens, effectively coating the surface of the invader, in order to prevent pathogens from entering or damaging healthy body cells. Antibodies can also stimulate other parts of the immune system (e.g. complement proteins) to destroy the pathogens.
        
        stimulating removal of pathogens by macrophages and other cells by coating the pathogen (opsonization)
        
        triggering destruction of pathogens by stimulating other immune responses such as the complement pathway
        
        preventing pathogens from entering or damaging cells by binding to them (neutralisation)
  - - - Coordinate the immune system and attack
    - - Memory T Cells
        
        Memorise immunity
        
        Have previously encountered and responded to an antigen
        
        Cells that keep track of how they killed the pathogen
        
        Memory T cells are a subset of infection- as well as potentially cancer-fighting T cells (also known as a T lymphocyte) that have previously encountered and responded to their cognate antigen; thus, the term antigen-experienced T cell is often applied.
      - Suppressor T Cells
        
        Protects healthy cells from viral attacks
        
        Stops immune resposnse
        
        Maintain tolerance to self-antigens, and prevent autoimmune disease.
      - Cytoxic T Cells
        
        Release enzymes that kill the cell
        
        Defend against the infected cell
        
        Helps with suicide
        
        If a body cell is infected and doesn't want to spread, it attaches itself to a normal cell presenting antigens. It then puts enzymes that makes holes in the cell.
        
        To activate a cytotoxic or helper T cell to proliferate and differentiate into an effector cell, an antigen-presenting cell provides two kinds of signals. Signal 1 is provided by a foreign peptide bound to an MHC protein on the surface of the presenting cell.
      - Helper T Cells
        
        Attach to B cells to tell genetic material of pathogen
        
        Help activate cytotoxic T cells to kill infected target cells.
        
        Help activate B cells to secrete antibodies and macrophages to destroy ingested microbes
      - Natural Killer T Cell
        
        Natural killer cells (also known as NK cells, K cells, and killer cells) are a type of lymphocyte (a white blood cell) and a component of innate immune system. NK cells play a major role in the host-rejection of both tumours and virally infected cells.
        
        NK cells provide rapid responses to viral-infected cells, acting at around 3 days after infection, and respond to tumor formation. Typically, immune cells detect major histocompatibility complex (MHC) presented on infected cell surfaces, triggering cytokine release, causing lysis or apoptosis.
        
        Natural killer cells (or NK cells) are a type of cytotoxic lymphocyte critical to the innate immune system. The role NK cells play is analogous to that of cytotoxic T cells in the vertebrate adaptive immune response.