Immunity Flashcards
Describe antibody structure
• Antibodies are large, complex protein molecules
• Each antibody consists of four polypeptides; two heavy chains and two light chains
• The two heavy chains (VDJ) and two light chains (VJ) join together to form a Y shaped molecule
• The amino acid sequence at the tip of the Y differs greatly between antibodies
* This amino acid variance is what gives the antibody its specificity for binding antigens
Describe the steps in cell mediated immunity
- Self cells or APCs displaying foreign antigens bind to T cells.
- Interleukins (secreted by APCs or helper T cells) costimulate activation of T cells.
- If MHC‐I and endogenous antigens are displayed on the plasma membrane, T cells proliferate, producing cytotoxic T cells. Cytotoxic T cells destroy cells displaying the antigens
- If MHC‐II and exogenous antigens are displayed on the plasma membrane, T cells proliferate, producing helper T cells. Helper T cells release interleukins (and other cytokines), which stimulate B cells to produce antibodies that bind to the antigens and stimulate nonspecific agents (NK and macrophages) to destroy the antigens
How are T-cells controlled?
• T-suppressor cells are T that close down the immune response after invading organisms are destroyed
• Suppressor T cells are sensitive to high concentrations of circulating lymphokine hormones, and release their own lymphokines after an immune response has achieved its goal
* This signals all other immune-system participants to cease their attack
Describe the process of thymocyte maturation.
*** Developing T cells in the thymus are known as thymocytes
• Immature thymocytes from the bone marrow migrate to the thymus
• One of the main functions of the thymus is to generate T cell receptors
• Segments within the antigen receptor genes are randomly translocated to generate receptor diversity
• Thymocytes are selected by interaction with thymic epithelial nurse cells
• If the thymocyte is able to recognise MHC in a right manner from a TEC, it will be selected and the TEC will begin providing it with thymus hormones to nourish the thymocyte
* Positively selected cells leave the thymus and accumulate in surrounding lymphoid organs
How are B cells activated?
B-cellsareactivatedby the binding of antigen to receptors on itscellsurface which causes thecellto divide and proliferate
How are Helper T cells activated?
- HelperT cellsbecomeactivatedwhen they are presented with peptide antigens by MHC class II molecules, which are expressed on the surface of antigen-presentingcells(APCs)
- Onceactivated, they divide rapidly and secrete small proteins called cytokines that regulate or assist in the active immune response
Describe the following components of the lymphatic system:
- Lymph nodes
- Spleen
- Tonsils
- Thymus
- Lymph nodes: are small lumps of tissue that contain white blood cells, which fight infection. They filter lymph fluid, which is composed of fluid and waste products from your body tissues
- Spleen: It is an organ that filters the blood and removes abnormal cells (such as old and defective red blood cells), and it makes disease-fighting components of the immune system (including antibodies and lymphocytes)
- Tonsils: They are two small pads of lymphatic tissue located each side of the back of the throat. They make antibodies and white blood cells (lymphocytes) to attack germs inside the mouth
- Thymus: It filters and monitors our blood content. It produces cells called T-lymphocytes which circulate around the body.
Define antigens and haptens
• Antigens are chemicals against which a specific immune response can be raised
* Haptens are the single components of an antigen that is responded to
What are the functions of antibodies
• They bind foreign molecules called antigens, inactivating them
• They can agglutinate pathogens together, making phagocytosis efficient
• They opsonise (making easier for phagocytosis)
Binding of antibodies can trigger complement activity. The activated complements (small proteins) insert into the cell membrane and form a pore, which disrupts the integrity of cell membrane can causes cell death
How does the complement system work?
• This system enhances, or complements, the ability of antibodies and phagocytes to clear microbes from an organism, promote inflammation and attack a pathogens cell membrane
* The complement system starts a long cascade of protein productions that either opsonize a pathogen for phagocytosis or lyse it directly by forming a membrane attack complex
Describe the five types of antibodies.
- IgA: DIMER- secreted into mucosal surfaces which prevents mucosal invasion into the body by pathogens. It is held together by a J chain and protected by a secretory components
- IgD: MONOMER- Found on the surface of B cells, activates basophils and mast cells
- IgE: MONOMER- found in allergen response
- IgG: MONOMER- only antibody capable of crossing placenta and providing passive immunity, most abundant in primary and secondary immunity
- IgM: PENTAMER- first type of antibody made when exposed to pathogens
How are antibodies so different from each other?
- When a stem cell changes to become a B cell, DNA segments for both heavy (VDJ) and light (VJ) chains are randomly combined and rearranged
- Somatic mutations also increase genetic diversity amongst antibodies
- Antibody specificity depends on the gene fragments used
What is opsonisation?
• Opsonization involves the binding of an opsonin, e.g an antibody, to a pathogen
* After opsonin binds to the membrane, phagocytes become attracted to the pathogen for engulfing purposes
What is chemotaxis?
• During growth and metabolism, bacteria release low molecular weight products
• For example, they may release FMLP during protein synthesis, AND, the peptidoglycan contains a unique sugar polymer
• Neutrophils have surface receptors that can detect these products and enables them to move towards the source
* This directional movement is termed chemotaxis
What are toll like receptors and what do they do?
• They are trans membrane proteins that detect PAMPS (pathogen associated molecular proteins) and send signals between downstream proteins which result in enhanced transcription of inflammatory genes
