Ch. 11 Part 4-Autoimuune Disease and Monoclonal Antibodies

Autoimmune Disease When the body attacks itself, leading to severe symptoms Occur when immune system attacks one or more self- antigens (usually proteins) Cause – Not well known – Genetic factors Susceptibility to disease is inherited – Environmental factors Increase in prevalence of diseases in developed world has increased in last 50 years Movement of people from areas where disease is rare to areas where it is more common – Showed increase chance of developing disease

How Auto-immune Disorders Occur During maturation of T-cells in THYMUS – Millions of cells destroyed because they have similar T-cell receptors that are complementary to self-antigens This is a good thing Prevents t-cells from attacking your own self-antigens – Some of the T-cell cells EVADE destruction This means you have t-cells that have receptors for self-antigens remaining in your body (NOT good) – Certain situations lead to ACTIVATION of faulty t-cells Activated to stimulate an immune response against your own body’s proteins Begins attack involving antibodies and killer t-cells against certain parts of your body Two types of attacks: – Localized (directed at one organ) – Whole body attack (extremely dangerous)

Myasthenia gravis (MG) Serious muscle weakness Autoimmune disease that targets neuromuscular junctions between motor neurons and skeletal muscle cells – Motor neurons  transmit impulses to muscle cells; terminal ends release ACETYLCHOLINE into gaps between motor neuron and muscle cell – Acetylcholine  cell signaling molecule Binds to receptors proteins on cell surfaces of muscle fiber Stimulates opening of channels in muscle fiber for sodium ions to move in Begins series of events leading to muscle contractions MG patients have helper T cells specific for cell surface receptors for acetylcholine – Under certain conditions, helper t-cells stimulate clone of b-cells to differentiate into plasma cells Plasma cells secrete antibodies that bind to receptor of acetylcholine, preventing acetylcholine from attaching to receptors (blocks transmission of signal) – Muscle fibers absorb receptor-antibody complexes and destroy them – No acetylcholine receptors = no muscle stimulation = no muscle contraction = muscle breaks down NOT an inherited condition Certain alleles involved in cell recognition put people at greater risk

Symptoms of MG Vary greatly Muscle weakness – Gets worse with activity – Improves with rest Affected muscles fatigue easily – Symptoms worse at end of day & after exercise

Treatments of MG Medications – Inhibit enzyme in synapses that break down acetylcholine Increases concentration of acetylcholine in synapse Enables acetylcholine's action of stimulating muscles to last longer Surgery – Removal of thymus gland It is site of maturation of helper T-cells Prevent maturation = prevents b-cells from making antibodies to acetylcholine receptors

Other Autoimmune Disorders Multiple Sclerosis – Develops when nerve cells in brain and spinal cord lose myelinated sheaths – Occurs anywhere in CNS – Degenerating areas called plaques, detected using MRI scans – Loss of myelin = loss of neural conduction of signals = loss of function of those areas controlled by CNS – Symptoms: muscle weakness, loss of sensory input from skin, poor vision, mental problems Rheumatoid arthritis – Occurs in joints – Tendons become inflamed – Constant muscle spasm and pain Type-1 insulin-dependent Diabetes – Caused by viral infection – Makes cells that secrete insulin in pancreas unrecognizable as self – Killer t-cells enter islets of Langerhans and destroy insulin producing cells

Review of Immune Response B cells become plasma cells that secrete antibodies in response to presence of a non-self antigen Antibodies bind to pathogens and kill them or mark them for destruction by phagocytes Antibodies have high degree of specificity Specificity makes them desirable to use in diagnosis and treatment of disease

Monoclonal Antibodies (Mabs) an antibody produced by a single clone of cells or cell line and consisting of identical antibody molecules Requires large number of cells of particular B cell clone to secrete the same antibody Problem in obtaining Mabs: – B cells that divide by mitosis do NOT produce antibodies – Plasma cells that secrete antibodies do NOT divide

Overcoming Hurdles 1970s Cell Fusion technique – Small # of plasma cells producing specific antibody fused with cancer cells (myeloma) to produce a HYBRIDOMA Cancer cells  divide indefinitely Fused cells could do two important things: – Divide by mitosis – Secrete antibodies – Antibodies are produced use lab animals Mice Rabbits

Producing Monoclonal Antibodies Inject organism with antigen that will stimulate production of antibody B lymphocytes in the organism will recognize this antigen and divide to form a clone of plasma cells able to secrete an antibody against it B lymphocytes are REMOVED from the SPELEN of that organism B lymphocytes are fused with a cancer cell to produce a HYBRIDOMA Hybridoma cells are identified – Individual cells are separated out – Each hybridoma cell is tested to see if it produces the antibody upon exposure to the pathogen – Any hybridoma that DOES produce antibody is cultured to produce clone of the cell so more antibodies can be secreted

Use of Mabs in Diagnosis Locate position of blood clot in body of person thought to have thrombosis – Antibodies are produced by injecting mouse with human fibrin Main protein found in blood clots – Mouse makes plasma cells that secrete antibody against fibrin – Plasma cells are collected from mouse’s spleen – Plasma cells fused with cancer cells to form hybridomas that secrete antifibrin antibody – Radioactive chemical that gives off gamma radiation is attached to antibody (so it can be traced) – Labeled antibodies introduced to patients blood – As Mabs is carried in blood, they bind to any fibrin molecules they come in contact with – Radioactivity given off by Mabs is used to tell doctor where the fibrin is located in body – Position of Mabs determines position of blood clot Locate Cancer Cells – Cancer cells have specific protein on their cell membrane surface – Proteins differ from normal cell surface proteins – Cancer proteins can be detected suing antibodies Identify exact strain of a virus or bacterial infection – Speeds up choice of most appropriate treatment Used in blood typing before transfusions Used in Tissue typing before transplants Used in an ELISA test to diagnosis infectious disease – Enzyme-Linked Immunoabsorbant Assay – Detects presence of certain antigens in the blood Used in Pregnancy Testing – Detect presence of human chronic gonadotrophin hormone (hCG) in urine hCG is a GLYCOPROTEIN hCG in relased when an embryo has implanted in the uterus – Antibodies on test strips attach to the hormone on urine, then react with other chemical on the strip to produce a color change (appears as stripes /colored lines) on a test strip

Use of Monoclonal Antibodies in Treatment Use of lab animals to make Mabs means that Mabs will trigger immune response when pit into humans Mabs need to be HUMANIZED: – Altering genes that code for heavy and light polypeptide chains of antibodies Enables genes to code for human sequence of amino acids – Changing type and position of sugar groups attached to heavy chains so that they are similar to human arrangements

Mabs Treatments Significant in treatments involving modifying immune response – Trastuzumab (Herceptin) Used in treatment of breast cancers Humanized mouse antibody Binds to receptor protein that is more numerous in cell surface membrane of cancerous cell Cells with times normal number of receptor protein are cancerous Antibody marks these cells for destruction by immune system – Ipilimumab More recent cancer therapy for melanoma Activates immune system Binds to protein produced by suppressor T-cells (who’s job is to reduce immune response) Immune response can then be maintained against cancer cells – Ifliximab Treatment of rheumatoid arthritis Mab binds to protein secreted by T cells that causes damage to cartilage in joints Blocks the action of this protein released by T cells Treatment given in 1-2 month intervals – Rituximab Controls B-lymphocytes Mab binds to cell surface receptor protein on surface of B-cells but NOT on surface of plasma cells After binding, causes variety of changes to that lead to cell death Treats diseases where there is an over production or inapporpriate production of B cells (leukemia or autoimmune diseases) Reducing # of B cells  reduces severity of diseases

Trastuzumab (Herceptin) Used in treatment of breast cancers Humanized mouse antibody Binds to receptor protein that is more numerous in cell surface membrane of cancerous cell Cells with times normal number of receptor protein are cancerous Antibody marks these cells for destruction by immune system

Ipilimumab More recent cancer therapy for melanoma Activates immune system Binds to protein produced by suppressor T-cells (who’s job is to reduce immune response) Immune response can then be maintained against cancer cells

Ifliximab Treatment of rheumatoid arthritis Mab binds to protein secreted by T cells that causes damage to cartilage in joints Blocks the action of this protein released by T cells Treatment given in 1-2 month intervals

Rituximab Controls B-lymphocytes Mab binds to cell surface receptor protein on surface of B-cells but NOT on surface of plasma cells After binding, causes variety of changes to that lead to cell death Treats diseases where there is an over production or inapporpriate production of B cells (leukemia or autoimmune diseases) Reducing # of B cells  reduces severity of diseases