Immunology: Key Terminology

Key Terminology

• Immunology studies the body's immune system and how it protects against disease.
• Microbes are microscopic organisms, some pathogenic and others beneficial
• Types of microbes include bacteria, viruses, fungi, protozoa, and algae
• An antigen is a substance that triggers an immune response in the body
• Antigens include bacteria, viruses, chemicals, toxins, and pollen
• Cytokines are small proteins that control or signal immune cell growth and activity
• Cytokines include interleukins, interferons, and lymphokines
• Antibodies are proteins produced by activated B cells to attack or weaken antigens
• Another name for antibodies is immunoglobulin
• Phagocytes are immune or white blood cells that engulf and digest pathogens
• Types of phagocytes include macrophages, neutrophils, monocytes, dendritic cells, and granulocytes
• Antigen-presenting cells (APCs) process antigens and expose them on the surface in recognizable T cell form
• APCs are crucial for initiating adaptive immunity
• Types of APCs include macrophages, dendritic cells and B cells
• Proteins within the immune system are large molecules of amino acid chains
• Proteins include Antibodies, cytokines-signalling proteins, complement proteins
• Opsonins coat pathogens, making them recognizable to phagocytes
• Examples of opsonins include IgG and C3b
• Phagocytosis is the process by which phagocytes engulf and digest pathogens
• Example of phagocytosis is neutrophils phagocytosing a bacterium
• Apoptosis is programmed cell death that eliminates unwanted cells and maintains tissue homeostasis
• The complement system aids in eliminating pathogens and helps the body heal after injury or infection
• Polymorphonuclear leukocytes (PMNs) are white blood cells that are the first line of defense in response to tissue injury
• PMNs include neutrophils, eosinophils, basophils, and mast cells

Key Organs & Tissues of the Immune System

• Primary organs specialize in creating immune system cells and lymphocytes
• Secondary organs are where immune system cells fight off foreign substances
• The bone marrow produces immune system cells, and B lymphocytes mature here
• The Thymus is where T lymphocytes mature and it coordinates immune responses
• The Spleen filters blood, stores platelets and white blood cells, and breaks down old red blood cells
• Tonsils prevent foreign substances from entering through the nasal and oral cavity
• Lymph nodes filter lymph fluid and traps pathogens to trigger antibody production
• Mucous membranes contain immune system cells and act as a protective barrier

Innate vs Adaptive Immunity

• Innate immunity is the first line of defense that is immediate or occurs within hours
• Innate immunity is non-specific and doesn't depend on antigens
• There’s no immunological memory in innate immunity
• Innate immunity includes barriers like skin, mucous membranes, and immune cells like phagocytes
• Adaptive immunity develops over time, over days or weeks
• Adaptive immunity is specific and antigen-dependent
• There is immunological memory in adaptive immunity
• Adaptive immunity involves B and T lymphocytes and the production of antibodies
• The oral mucosa is a physical barrier that contains immune cells
• Saliva contains IgA and antimicrobial peptides
• Tonsils trap pathogens and activate immune response
• Anatomic barriers are the initial physical barriers that stop pathogens
• Examples of Anatomic barriers Skin, mucous membranes, respiratory tract, and oral and nasal cavities
• Physiological barriers regulate immune response through body systems
• Physiological system involves Low pH/acid in the stomach, body temperature and chemical mediators; saliva, tears
• Phagocytic or Endocytic barriers engulf and digest foreign pathogens
• Macrophages and neutrophils are pathogen targeted sites within the body
• Inflammatory barriers detect and trigger immune response to injury to protect from pathogens and tissue damage
• Inflammatory involves Cytokine and histamine release at the site of trauma or infection either internally or externally

Cells of the Immune System

• Macrophages perform phagocytosis and antigen presentation to T cells and also release cytokines
• Natural killer cells target tumor cells and viruses
• Neutrophils are granulocytes and phagocytes that target bacteria and fungi
• Eosinophils are granulocytes that target parasites and allergic tissues
• Basophils are granulocytes that target various allergic reactions
• Mast cells produce histamine and heparin
• Dendritic cells are main antigen-presenting cells, and they capture and process pathogens
• T cells differentiate to recognize antigens with MHC on antigen presenting cell
• B cells mature to secrete antibodies to attack antigens
• T lymphocytes develop from stem cells and produce create signals; destroy harmful pathogens
• Dendritic cells link innate immunity and adaptive immunity; process and present antigens to lymphocytes to initiate immune response
• Polymorphonuclear leukocytes contain enzymes that are realized during infections
• Basophils and Eosinophils and Neutrophils are types of polymorphonuclear leucoytes
• Natural killer cells contain enzymes destroy tumor cells or virus infected cells
• Red blood cells recognize and adhere to antigens and promote phagocytosis
• Platelets instruct innate immune cells and influence antibody production and T-cell polarization
• Mast cells release cytokines once activated
• Granulocytes release enzymes to fight infection and inflammation

Cytokines

• Cytokines impact the immune system by modulating it
• Chemokines control the movement of immune cells in tissues and allow innate immune system function
• Interlukins control cellular communication
• Monokines are produced by monocytes and macrophages to start innate response
• Lymphokines enhance or suppress immune response
• Interferons (IFN) are signaling protein
• Tumor Necrosis Factors (TNF) assist in cellular survival, proliferation and differentiation
• Colony Stimulating Factors (CFS) activate intracellular pathways for blood cell proliferation and differentiation

Antibodies, Adaptive Immunity

• Antibodies are created by activated B cells
• Antibodies recognize, bind to antigens and mark them for destruction
• Activated B cells produce antibodies in response to pathogens or vaccines
• There are five Immunoglobulin types, each playing different roles in fighting infection
• Antibodies do not eliminate viruses during infection
• Humoral/antibody-mediated immunity is a type of adaptive immunity where B cells produce antibodies
• The process of humoral/antibody-mediated immunity starts when B cells with antigen receptors bind to antigens
• T helper cells secrete cytokines to help antibodies multiply and direct direction
• Antibodies will bind to antigens for destruction by the complement system, opsonisation and phagocytosis
• Adaptive Immunity has both humoral and cell mediated response
• Cell mediated response mostly eliminates microbes that survive pathogen destruction and infect non-phagocytic cells
• The cell mediated response mostly eliminates viruses or infections in cell
• Cell mediated response assists in transplant rejection
• Adaptive immunity is when T Cells stimulate attack on virus/cancer cells
• When someone needs help destroying intracellular pathogens, their Immune cells produce cytokine/mediators and attack pathogen

Immunoglobulin Types

• There are two forms of Immunoglobulin A: secretory and serum
• Secretory IgA is found in linings of the respiratory and digestive system, saliva, tears and breast milk
• Secretory IgA is an antiseptic part of mucus membranes
• Immunoglobulin A (IgA) activates the complement system
• Serum IgA cannot activate the complement system
• There are low levels of Immunoglobulin D (IgD) in blood, cannot activate complement system
• IgD is found on the surface of B cells
• Half of antigen specific receptors on B lymphocyte membranes are IgD
• IgD assists is promoting B cell maturation and activation
• Immunoglobulin E (IgE) is found in skin, lungs and mucus membranes
• IgE attaches to mast cells and basophils, triggering release of histamine
• High levels of IgE are found in allergies such as hay fever and asthma
• IgE can cause allergic reactions
• Immunoglobulin (IgG) is the most common antibody in blood tissue and fluid
• IgG protects the body from viral and bacterial infections and diffuses toxins
• IgG occurs in secondary immune response
• IgM is found in the blood and lymph system and has a large role in immune regulation
• IgM is the largest immune molecule and is short lived
• IgM is usually the first antibody created to defend against infections

Acquired/Adaptive Immunity

• Passive immunity is gained through natural or artifical methods
• Active immunity is also gained through natural or artificial methods
• Natural passive immunity involves a mother's antibodies passing through the placenta or breast milk
• Artificial passive immunity involves the therapeutic use of snake toxin or antibody transplant
• Natural active immunity involves antibodies developed in response to infection
• Artificial active immunity involves antibodies developed in response to vaccination
• Passive immunity involves injecting exogenous antibodies to target an antigen or toxin
• Passive immunity is short duration, to defend against infection
• Used in patients with high risk of infection, and helps patients with insufficient immunity
• Active immunity involves production of antibodies after exposure to antigen, and has specific response with memmory

Immune Disorders

• Hypersensitivity is an overactive immune response that causes gross tissue damage when triggering and meeting an antigen
• Type 1 Hypersensitivity is called Anaphylaxis, is rapid, and is caused by exposure to an allergen
• Anaphylaxis causes secrete Immunoglobulin E which binds to mast cells and basophils who are sensitized
• In succeeding allergen exposure, histamine will be released initiating degranulation, leads to allergy
• Treating Type 1 Hypersensitivity can be avoided with medication or immunotherapy
• Type 2 hypersensitivity is antibody mediated, lasting between 2- 24 hours
• The Antibodies IgG and IgM bind to the antigen on cells who bind to complement system and killer cells
• Type 2 results in damaged cells and no cure
• Triggers can only avoided with medication
• Type 3 Hypersensitivity is an immune complex lasting hours, days, or weeks
• Antigen and Antibody binding result in Immunoglobulin which then triggers complement pathway
• Treatments rely on trigger avoidance with no cure
• Type 4, sometimes referred to as the T-Cell Mediated Reaction, occurs 2+ days later
• Trigger results in prolonged inflammation and often relies on trigger avoidance to counter
• Immunodeficiency is an ineffective immune response that may be compromised or absent requiring medication
• Both innate and adaptive immunity can result in autoimmune
• Diseases immunocompromised include: Poorly controlled diabetes, HIV infection, Anaemia, Some malignancies, Malnutrition, Vit D deficiency, kidney failure or absent Spleen
• Primary immunodeficiency is a rare life-threatening disease that may be genetic
• B-cell and T-cell deficiencies are adaptive, as well as severe combined SCID adaptive, unlike innate with disorders
• Secondary immunodeficiency is related to other conditions or infections and can be resolved

Key Considerations for Dental Care

• With current or past allergies
• Ensure allergies in patients are asked about any treatment
• Autoimmunity involves an Inappropriate reaction to self-antigens, self antigen breakdown
• Patients with risk of increased autoimmunity with increased age, as T-cells are suppressed
• Autoimmune disease is a Chronic and progressive disorder affecting Healthy tissue with antibodies attacking own immune system
• This attack will cause tissue destruction of target organ
• Immunosuppression, steroidal and non-steroidal can assist with treatment of autoimmune diseases
• Oral signs are usually the initial manifestation symptom of autoimmunity and its effects
• Early diagnosis through taking medical history can aid with treatment and quality of life