Bellwork Discuss with your group what you think is happening in the following processes. Why does your body undergo an allergic reaction? Why do some people’s bodies attack themselves (autoimmune diseases)? How does AIDS escape the human immune systems? Why do we have an inflammatory response when we are injured?

Innate immunity Present before any exposure to pathogens and is effective from the time of birth Involves nonspecific responses to pathogens Innate immunity consists of external barriers plus internal cellular and chemical defenses

Acquired immunity, AKA adaptive immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances It involves a very specific response to pathogens

Major parts of Innate Immunity Barrier defenses Phagocytosis Antimicrobial peptides Inflammatory response Natural killer cells

Innate Immunity - Phagocytosis Groups of pathogens are recognized by TLR, Toll-like receptors Once recognized, cells engulf the pathogen

Innate Immunity - Phagocytosis There are different types of phagocytic cells: Neutrophils engulf and destroy microbes Macrophages (big eaters) are part of the lymphatic system and are found throughout the body Eosinophils discharge destructive enzymes to kill multicellular parasites Dendritic cells stimulate development of acquired immunity

Innate Immunity – antimicrobial peptides (AKA proteins) Interferons – induce nearby viral infected cells to secrete substances that inhibit viral reproduction Complement system- Proteins in the blood plasma that fight infection. Can react to form a complex that leads to lysing of invading cells

Innate Immunity – Inflammatory response Changes brought about by chemical signal At the site, mast cells in the connective tissue release histamine Histamine triggers nearby blood vessels to dilate and become more permeable This helps deliver antimicrobial proteins, neutrophils and macrophages Pus, a fluid rich in white blood cells, dead microbes, and cell debris, accumulates at the site of inflammation

Pathogen Splinter Chemical signals Macrophage Fluid Mast cell Fig. 43-8-3 Pathogen Splinter Chemical signals Macrophage Fluid Mast cell Capillary Phagocytosis Figure 43.8 Major events in a local inflammatory response For the Cell Biology Video Chemotaxis of a Neutrophil, go to Animation and Video Files. Red blood cells Phagocytic cell

Check for Understanding On a sheet of paper, write an essay to describe the inflammatory response

Innate Immunity - Natural Killer Cells Help recognize and eliminate certain diseased cells

Define Antigen Antibody lymphocytes

Acquired Immunity White blood cells recognize and respond to antigens (foreign molecules) and then create immunological memory Lymphocytes that mature in the thymus are called T cells, and those that mature in bone marrow are called B cells

Acquired Immunity B cells and T cells have receptor proteins that can bind to foreign molecules Each individual lymphocyte is specialized to recognize a specific type of molecule

Acquired Immunity – With all the variation in receptors, why does it not attack itself? As lymphocytes mature in bone marrow or the thymus, they are tested for self- reactivity Lymphocytes with receptors specific for the body’s own molecules are destroyed by apoptosis, or rendered nonfunctional

Acquired Immunity B cells can make receptors that detach from the cell membrane (antibody) Epitope – a foreign molecule that a specific antibody or lymphocyte binds to

But Before we talk about that… lets see how it all begins A cell engulfs the pathogen (either a regular cell, dendritic cells, macrophages, and B cells) Molecules within the cells attach to the antigen and present it to T cells

Infected cell Antigen fragment Class I MHC molecule T cell receptor Fig. 43-12 Infected cell Antigen fragment Class I MHC molecule T cell receptor (a) associates with MHC recognizes combination Cytotoxic T cell (b) Helper T cell Class II MHC Antigen- presenting cell Microbe 1 2 1 Figure 43.12 The interaction of T cells with antigen-presenting cells Class II MHC is found in specialized phagocytic cells, such as dendritic cells, macrophages and B cells. These present the antigen to either cytotoxic T cells or Helper T cells Class I MHC is found in all body cells and can only present it to cytotoxic T cells

Once they recognize the antigen they call for help! Acquired immunity has two branches: the humoral immune response and the cell- mediated immune response Humoral immune response involves activation and clonal selection of B cells, resulting in production of secreted antibodies Cell-mediated immune response involves activation and clonal selection of cytotoxic T cells *Helper T cells can stimulate either response

A focus on cell mediated response Activated helper T cells secrete cytokines that stimulate other lymphocytes Includes cytotoxic T cells which kill the infected cells

A focus on cell mediated response The binding of a mature lymphocyte to an antigen induces the lymphocyte to divide rapidly This proliferation of lymphocytes is called clonal selection Two types of clones are produced: short- lived activated effector cells and long- lived memory cells Lets see it again!

Now, the humoral response

A focus on the humoral response The helper T cell sends signals to recruit B cells The B cells proliferate into memory cells and plasma cells

A focus on the humoral response The B cells send out antibodies

The Role of Antibodies in Immunity Neutralization occurs when a pathogen can no longer infect a host because it is bound to an antibody Opsonization occurs when antibodies bound to antigens increase phagocytosis Antibodies together with proteins of the complement system generate a membrane attack complex and cell lysis

There are different types of antibodies

Why is our body better at fighting a pathogen off the second time? The first exposure to a specific antigen represents the primary immune response During this time, effector B cells called plasma cells are generated, and T cells are activated to their effector forms In the secondary immune response, memory cells facilitate a faster, more efficient response

Summarize Compare and contrast B and T cells

So now… what are vaccinations and how does this help our immune system? We introduce the epitope to our bodies so our body makes memmory cells, then when our immune system is faced with the actual pathogen, it can quickly destroy it

What are allergies? Allergies are exaggerated (hypersensitive) responses to antigens called allergens In localized allergies such as hay fever, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells

Allergies

Autoimmune disorders What do you think has gone wrong? The mechanisms for detecting receptors that attack its own cells are not working properly

Bellwork Discuss with your group why your immune system does not have a secondary response to AIDS like most other viruses. How does it escape the immune system?

AIDS Human immunodeficiency virus (HIV) infects helper T cells The loss of helper T cells impairs both the humoral and cell-mediated immune responses and leads to AIDS HIV eludes the immune system because of antigenic variation and an ability to remain latent while integrated into host DNA