A&P - Immunity
What are the key characteristics of the cell-mediated response?
1) MHC I molecules present antigens on any infected nucleated cell 2) Cytotoxic T killer cell participation 3) primarily respond to intracellular infections 4) results in activation and proliferation of cytotoxic T killer cells
What are the key characteristics of the humoral response?
1) MHC II molecules present antigens on APCs 2) B cell mediated 3) may require T helper cell activation 4) primarily respond to extracellular antigens 5) results in antibody production by activated plasma cells
What are the three functions of antibodies?
1) Neutralize bacterial toxins 2) Neutralize viruses 3) Opsonize (tag for destruction) encapsulated bacteria *Antibodies are also referred to as immunoglobulins; these exist either in solute form as cell secretions or membrane-bound to B cells.
What are the three levels of the immune system?
1) Non-specific barriers 2) Non-specific cellular response 3) Specific response
What is the role of the complement system in the humoral response?
Antibodies created by the humoral response can activate the complement system, which serves three functions: 1) Tag invading cells for phagocytosis 2) Release chemotactic mediators 3) Construct a membrane attack complex (MAC) which creates a pore in the cell membrane and lyses the cell
Describe the role of B cells
B cells are responsible for humoral immunity through their differentiation and proliferation of plasma cells which produce of antibodies (immunoglobulin); have membrane bound immunoglobulin; can present antigens to T cells; also differentiate into memory cells upon activation
Contrast the two important classes of MHC complexes
MHC I is present on most nucleated cells. Cytotoxic T-killer cells respond to these aand initiate death of virus-infected cells. MHC II has more limited distribution, is present only on antigen presenting cells (APCs) including B cells, dendritic cells, and induced macrophages. The functions of both complexes are to bind with antigens and interact with T cells.
What is the role of mast cells and neutrophils in immunity?
Secrete cytokines, which stimulate activation of B and T cells; neutrophils are involved in acute inflammation
more about MHC II?
T-helper cells with CD4+ receptors check the MHC II molecule on APCs (B cells, dendritic cells, macrophages) and initiate either the cell-mediated response or the humoral response based on the presenting antigen.
After tissue injury, how is hyperemia (increasing blood flow beyond normal) achieved?
Through vasodilation; cells secrete vasoactive chemicals (ie: histamine, leukotrienes, and other cytokines) that dilate the blood vessels
Describe the subepithelial areolar tissue's natural defense
Viscous barrier of hyaluronic acid that is hard for microbes to migrate through (Some microbes produce an enzyme called hyaluronidase, which breaks the layer down into a thinner consistency)
What are the four characteristics of acquired immunity?
*1) Specificity - only responds to certain entities 2) Adaptiveness - may be able to respond to previously unseen molecules 3) Discriminate - can identify self v. non-self *4) Memory - retains a record of previously encountered antigens for future response
Describe the skin's natural defenses
*Keratin-tough protein that few pathogens can penetrate; also provides a water barrier and the dryness prevents bacterial growth *Acid mantle-thin film of lactic acid from sweat that inhibits bacterial growth (more bacterio-static than anything) *Defensins and cathelicidins-peptides that destroy bacteria, viruses, and fungi
Describe the humoral response
1) A foreign invader is phagocytized by an APC, and its antigen is presented on the APC's MHC II 2) A helper T cell binds to the antigen of the MHC II and proliferates 3) The same antigen binds to a B cell's membrane-bound antigen and presents on its MHC II 4) The T helper cell recognizes the presenting antigen on the B cell and activates it 5) B cell differentiates into plasma cells and memory cells, which proliferate 6) Plasma cells produce antibodies to neutralize or opsonize the invader, or trigger the complement system
Describe the cell-mediated response
1) A nucleated cell becomes infected by a virus (cancerous cells also initiate cell-mediated response) 2) Antigens from the infecting virus present on the cell's MHC I 3) Cytotoxic T killer cell binds to the infected cell, become activated and proliferate 4) Bound T killer cell releases perforin, which causes the infected cell to lyse
Other sources indicate five functions of antibodies. What are they?
1) Agglutination - bind MO together to reduce total infectious units 2) Opsonization - coating antigen with antibodies enhances phagocytosis 3) Neutralization - blocks adhesion of viruses, bacteria and toxins 4) Antibody-dependent cell-mediated cytotoxicity - antibody attachment causes cell destruction 5) Activation of complement system - causes inflammation and lysis
What are the five characteristics of antigens?
1) Foreign (??) 2) High molecular weight 3) Chemically complex 4) Degradable 5) Dosage and route of administration also important
What are the three categories of lymphocytes
1) T cells - thymus derived, initiate humoral immunity 2) B cells - bone-marrow derived, initiate cell-mediated immunity 3) Natural killer cells - destroy tumor and virus-infected cells without prior exposure or sensitization
How do APCs process and present antigens on MHC II molecules?
1) They phagocyte (macrophage, dendritic cell) phagocytizes a MO (e.g. bacteria) and digests it via the action of lysosomes 2) Digested MO is broken down into peptide chains (antigens) 3) The peptide binds to an MHC II molecule and migrates to the cell membrane 4) The MHC II molecule with the bound antigen presents itself to T helper cells that initiate the cell-mediated or humoral responses
What are the two types of T cells and their roles?
1) helper CD4 T cells - secrete cytokines to stimulate CD8 T cells and macrophages, stimulate B cell proliferation, help convert B cells to plasma cells, some serve as memory; activated by antigen MHC2 complexes on antigen presenting cells 2) cytotoxic CD8 T cells - destroy target cells by binding to the antigen and releasing damaging enzymes or chemicals and chemotactic mediators; seek out tumor and virally infected cells; activated by antigen MHCI complexes and CD4 T cells
Briefly describe the cellular mediated immune response
1. Antigen presentation 2. Antigen recognition by T cells 3. Costimulation (cytokine release causing T cell proliferation) 4. Attack
Briefly describe the humoral immune response
1. Antigen recognition (Immunocompetent B cells are exposed to an antigen; Antigen only binds to B cells with complementary receptors) 2. Antigen presentation (B cell internalizes antigen and displays proccessed epitope. Helper T-cell binds to B-cell and secretes interleukin) 3. Clonal selection (Interleukin stimulates B cell to divide repeatedly and form a clone) 4. Differentiation (Some cells of the clone become memory B cells. Most differentiate into plasma cells) 5. Attack (Plasma cells synthesize and secrete antibody)
List and briefly describe the four types of T cells
1. Cytotoxic T cells (carry out the attack on foreign cells) 2. Helper T cells (play key roles in both humoral immunity and nonspecific resistance) 3. Regulatory T cells (AKA T suppressors) (limit the immune response by inhibiting multiplication and cytokine secretion by other T cells) 4. Memory T cells (responsible for memory in cellular immunity)
List four end results of the complement system
1. Inflammation 2. Immune clearance 3. Phagocytosis 4. Cytolysis
Once released by a plasma cell, antibodies use four mechanisms to render antigens harmless. List these.
1. Neutralization (Mask the pathogenic region of an antigen) 2. Complement fixation (Antibodies IgM and IgG bind to enemy cells and change shape, exposing the complement-binding sites; the complement then binds to the enemy cell surface leading to inflammation, phagocytosis, immune clearance, and cytolisis) 3. Agglutination (sticks antigen molecules together, immobilizing them) 4. Precipitation (antibodies link antigen molecules-not whole cells-together...similar to agglutination)
Fever usually does more good than harm. List three ways that fever is beneficial.
1. Promotes interferon activity 2. Elevates metabolic rate and accelerates tissue repair 3. Inhibits reproduction of bacteria and viruses
Describe how neutrophils get to an area of tissue injury (ie: the process of margination and diapedesis)
1. Release of inflammatory chemicals 2. Stimulation of leukocyte margination (adhesion to the capillary wall) 3. Diapedesis (crawling through the capillary wall) 4. Chemotaxis (the process by which neutrophils are attracted to areas of inflammation) 5. Phagocytosis ensues (engulfing bacteria and other pathogens)
What is the Major Histocompatibility Complex?
A highly polymorphous membrane protein (most polymorphic gene in the body) that selectively binds antigens for presentation to cells of immunity, such as T and B cells. It is crucial for T cell response (adaptive immunity) and also self/non-self recognition, e.g. organ transplant rejection.
Briefly describe inflammation
A local, non-specific defensive response to tissue injury of any kind; its general purposes are to limit the spread of pathogens and ultimately destroy them; remove the debris of damaged tissue; and initiate tissue repair
Which cells are antigen presenting cells (APCs) and what is their role?
APCs include macrophages, dendritic cells and B cells. These present antigens via MHC II to lymphocytes to trigger immune response.
What are the subdivisions of acquired immunity?
Active and passive immunity, which are both further subdivided into natural or artificial
Describe active immunity and its subdivisions
Active immunity involves exposing an individual to an antigen, causing the body to develop antibodies. Active natural immunity is the exposure to a live antigen, such as infection. Active artificial refers to acquiring immunity by purposefully introducing antigens to the body, such as vaccines which introduce dead or attenuated antigens.
Describe platelet-derived growth factor
Blood platelets and endothelial cells in an area of injury secrete this; it stimulates fibroblasts to multiply and synthesize collagen
Is the complement system specific or nonspecific?
Both
more about MHC I?
Cytolitic T-killer cells or NK cells with CD8+ receptors check MHC I molecules on all nucleated cells of the body for evidence of infection of the cell and initiate cell death based on the presenting antigen.
What is opsonization?
Complement system coats microbial cells and serves as binding sites for phagocyte attachment; opsonization effectively "butters up" foreign cells to make them more appetizing for phagocytosis...allows for better immune clearance
What is the membrane attack complex?
Conglomeration of complement proteins which form a ring; the complex forms a hole within the target cell, causing the cell to rupture
What is the class of chemicals that regulate inflammation and immunity called?
Cytokines
What is the importance of MHC diversity?
Diversity drives susceptibility and resistance to disease, and its dysfunction gives rise to autoimmune diseases.
When a molecule is too small to be considered an antigen by itself and has to bind to a host macromolecule to stimulate an immune response it's called a _____.
Hapten
Describe Reye Syndrome
Hypersensitivity to aspirin in children younger than 15; characterized by swelling of brain neurons and fatty infiltration of the liver and other viscera
What are the four cell categories of acquired immunity?
Lymphocytes Antigen presenting cells Mast cells Neutrophils
List the non-specific leukocytes
Neutrophils, eosinophils, basophils, monocytes
Which of the three levels of defense represent innate immunity? Which represent acquired immunity?
Non-specific barriers and non-specific cellular response represent innate immunity. Specific response represents acquired immunity.
Describe passive immunity and its subdivisions
Passive immunity occurs when antibodies are transferred from one person to another. Passive natural involves transferral of antibodies via breast milk or across the placenta from mother to fetus. Passive artificial results from the injection of antibodies from a person or animal into another person.
Describe how mucous membranes in the digestive, respiratory, urinary, and reproductive tracts provide natural defense
Physically ensnare microbes Mucus, tears, and saliva also contain lysozyme, an enzyme that destroys bacteria by dissolving their cell walls
What are the four cardinal signs of inflammation?
Redness, swelling, heat, and pain
What is an epitope?
The certain region of an antigen molecule that stimulates immune response. One antigen molecule typically has several diff epitopes, and therefore can stimulate production of different antibodies
What are interferons?
When certain cells (esp leukocytes) are infected with viruses, they secrete proteins called interferons; these are like the cell's last words...they alert nearby cells and protect them from becoming infected. They bind to surface receptors on those cells and activate second-messenger systems that induce the synthesis of antiviral proteins and disallow viral replication
In addition to causing vasodilation, these chemicals cause increased ______, allowing for easier movement of fluid, leukocytes, and plasma proteins from the bloodstream into the surrounding tissue.
capillary permeability
