Ch. 43 – the immune system Essential Knoweldge 2.D.4 (a-b) Big Idea 2

What you must know: Several elements of an innate immune response The differences between B and T cells relative to their activation and actions. How antigens are recognized by immune system cells The differences in humoral and cell-mediated immunity Why Helper T cells are central to immune responses

Chapter 43 Warm-Up Define the following terms: Pathogen – a bacteria or virus Antigen –  the protein on the surface of a cell (bacterium, fungus or virus) that our bodies recognize as a foreign substance and triggers the immune system into producing antibodies specific to that antigen phagocytosis (cell eating) Phagocytes – types of white blood cells that ingest invading organisms and initiate the inflammatory response Macrophages - a specific type of phagocyte found throughout your body -eat the antigens; this causes swelling. Macrophages secrete lysosomes into the antigen to destroy it; problem – it will attack anything not us, including organ transplants lymphocytes – types of white blood cells

Overview A virus uses the machinery of your cells to make more copies of itself, until it destroys the cell; when that happens, the cell bursts and releases all the new viruses into your body to repeat the process Without the immune system, we’d be in big trouble.

Types of Immunity Adaptive Immunity (humoral or cell mediated) Innate Immunity (skin, phagocytes) Adaptive Immunity (humoral or cell mediated) Non-specific Present at birth (passed from mother through placenta) All plants & animals Rapid response (fever, inflammation, etc) Pathogen-specific Develops only after exposure to inducing agents (virus, bacteria, etc) Only in vertebrates Involves B and T cells

Plant Defenses Nonspecific responses (have no immune system response) – it kills anything that invades or moves inside the organism Receptors recognize pathogen molecules and trigger defense responses Thicken cell wall, produce antimicrobial compounds, cell death Localize effects

Plant and Animal defense mechanisms – Innate Immunity Hypersensitive response (a plant can sense proteins given off by bacteria by using its “R” gene) – reminder from ch. 39, plant responses Lets off an oxidative burst, that kills the cells, even if it’s not infected It also gives off a protein that changes the cell walls of all the adjacent cells Doesn’t have memory, so it will go through the same process if it’s infected again

Innate Immunity - How Immunity Works - Skin This is the first layer of defense Creates a barrier Has a low pH (which makes it hard for some bacteria to live there) Chemicals on the surface of our skin disrupt certain viruses Bacteria (normal flora which just lives there) crowd out our skin which makes it hard for other substances to enter Certain cells of the mucous membranes produce mucus A viscous fluid that traps microbes and other particles

Skin cont. If you get a cut, then there is a breach in your first defense Internal cellular defenses Depend mainly on phagocytosis (cell eating) Phagocytes ingest invading microorganisms Initiate the inflammatory response Inflammation occurs (chemicals are released that causes our body to respond) For example – acne (an infection in the pores of your skin)– bacteria are living and eating under our skin Macrophages (a specific type of phagocyte found throughout your body) enter and eat the invaders; this causes swelling. Macrophages secrete lysosomes into the antigen to destroy it problem – it will attack anything not us, including organ transplants

Phagocytosis

Inflammatory Response

Lymphatic System: involved in adaptive immunity

Adaptive Response Lymphocytes (WBCs): produced by stem cells in bone marrow T cells: mature in thymus helper T, cytotoxic T B cells: stay and mature in bone marrow plasma cells  antibodies

Aquired Immunity - Specific immune response Specific immune responses mean that we have generated antibodies for a specific virus, so we won’t get the same cold twice Pathogens have specific proteins on their surfaces (antigens) To fight them, we have structures called antibodies (proteins produced by our bodies) They have very specific shapes that will allow them to connect to the antigen; this helps the macrophages find them, and it also makes it harder for the antigens to do their job

Specific Immune Responses Cont. – B lymphocytes B Lymphocytes are 1 type of white blood cells or phagocytes (attack viruses in our bodies) Made in bone marrow Create a humoral response (means, “in the fluid” or in the “humors” – like blood, lymph material, insterstitial fluid) A naïve B cell senses the shape of the antigen, sends out a chemical message, and the B lymphocytes produce the antibodies specific for that antigen Memory B cells are then created to help give us immunity for the rest of our lives

Specific Immune Response cont - T Lymphocytes T Lymphocytes target and kill the cells that are already infected (responsible for what’s called a cell-mediated response) Created in the thymus (a gland on top of our heart; this is where they get the “T” from) Create Killer T Cells or Cytotoxic T Cells (a type of T lymphocytes) which target cells that are infected, docks next to them, and kills them Causes cell death

Major Histocompatibility Complex (MHC) Proteins displayed on cell surface Responsible for tissue/organ rejection (“self” vs. “non-self”) B and T cells bind to MHC molecule in adaptive response Class I: all body cells (except RBCs) Class II: displayed by immune cells; “non-self”

Helper T Cells You have an antigen that is eaten by a macrophage, which chops up the antigen and produces pieces of it on it’s surface using a chemical called MHC2 (major histocompatibility complex); you then get a Helper T cell (another type of T Lymphocyte) which docks on the macrophage and senses the shape of that antigen using another chemical called CD4; this initiates both the humoral and cell-mediated responses A Helper T cell tells the shape of the antigen to the B cells so they can make more antibodies, tells it to the macrophages which will then eat the invaders, and they activate the killer T cells so they can kill the infected cells Helper T cells basically initiate the entire immune response Acquired immunodeficiencies range from temporary states to chronic diseases These are the cells that are being infected by HIV

Antigen: substance that elicits lymphocyte response Antibody (immunoglobulin – Ig): protein made by B cell that binds to antigens

Cell-Mediated Immune Response Humoral Immune Response Antigen-presenting cell Cell-Mediated Immune Response (T Cells) Humoral Immune Response (antibodies) Helper T cell B cell Cytotoxic T cell Plasma cell tag for destruction Identify and destroy Infected cell Antibodies

AIDS People with AIDS are highly susceptible to opportunistic infections and cancers that take advantage of an immune system in collapse You don’t die from aids, you die from a secondary infection Because AIDS arises from loss of helper T cells, it impairs both the humoral and cell-mediated immune responses The loss of helper T cells results from infection by the human immunodeficiency virus (HIV)

Pathogens (such as bacteria, fungi, and viruses) INNATE IMMUNITY (all animals) Barrier defenses: Skin Mucous membranes Secretions Recognition of traits shared by broad ranges of pathogens, using a small set of receptors • Internal defenses: Phagocytic cells Natural killer cells Antimicrobial proteins Inflammatory response • Rapid response Figure 43.2 Overview of animal immunity. ADAPTIVE IMMUNITY (vertebrates only) Humoral response: Antibodies defend against infection in body fluids. Recognition of traits specific to particular pathogens, using a vast array of receptors • Cell-mediated response: Cytotoxic cells defend against infection in body cells. • Slower response

Autoimmune Diseases In individuals with autoimmune diseases, the immune system loses tolerance for self and turns against certain molecules of the body Rheumatoid arthritis is an autoimmune disease leading to damage and inflammation of joints Multiple Sclerosis

Blood Types Antigens on red blood cells determine whether a person has blood type A (A antigen), B (B antigen), AB (both A and B antigens), or O (neither antigen) Antibodies to nonself blood types exist in the body Transfusion with incompatible blood leads to destruction of the transfused cells Recipient-donor combinations can be fatal or safe

Cancer and Immunity The frequency of certain cancers increases when adaptive immunity is impaired 20% of all human cancers involve viruses The immune system can act as a defense against viruses that cause cancer and cancer cells that harbor viruses In 2006, a vaccine was released that acts against human papillomavirus (HPV), a virus associated with cervical cancer

Immunological Memory Primary immune response: 1st exposure to antigen Memory cells: Secondary immune response: repeat exposure  faster, greater response

B cells that differ in antigen specificity Antigen Antigen receptor Figure 43.14 B cells that differ in antigen specificity Antigen Antigen receptor Figure 43.14 Clonal selection. Antibody Memory cells Plasma cells

Passive immunity: via antibodies in breast milk Immunizations/vaccines: induce immune memory to nonpathogenic microbe or toxin Passive immunity: via antibodies in breast milk Allergies: hypersensitive responses to harmless antigens Autoimmune Diseases: Lupus, rheumatoid arthritis, Type I diabetes, multiple sclerosis HIV: infect Helper T cells AIDS = severely weakened immune system

Secondary Exposure If you are exposed to a virus that you have previously experienced, you would already have antibodies, memory B and Memory T cells that can be quickly produced and fight off the cold before you feel its effects.

Virtual Lab http://media.hhmi.org/biointeractive/vlabs/immunology/index.html