The Body's Defenses The Immune System

Main Point #1 The body is first protected by a barrier

The Outermost Barriers Slightly acidic, dry skin Prevents living things from growing on us The Integumentary System

Skin Secretions Make skin acidic Saliva, tears and mucous all wash away most harmful bacteria Secretions contain antibacterial proteins such as lysozyme

Mucus Traps microbes and particles Swallowed and acid from the stomach kills bacteria We also expel mucus through sneezing and runny noses (rhinorreah)

Main Point #2 We have a non-specific immune system that attacks any invading pathogen

Non-Specific Responses The body has white blood cells that attack any foreign invaders

Neutrophils WBCs attracted to damaged cells Engulf and destroy microbes via phagocytosis 60-70% of all WBCs Short life-span

Monocytes More effective phagocytes Form macrophages Attach to bacterial surfaces and digest bacteria with lysosomes Only about 5% of WBCs

Eosinophils Fight off larger invaders Shoot enzymes at large parasites such as blood flukes

Natural Killer Destroy virus- infected body cells Burst the membrane of a cell, destroying it Protects against viral takeovers and tumors

Inflammatory Response Cuts or bacterial infections cause the release of histamines by basophil and mast cells This causes blood to flow to capillaries to cuts and infections

Inflammation con. Increased blood flow brings clotting factors as well as WBCs to attack the invader Fluid and WBCs leak out of capillaries, which is why injured areas swell

Main Point #3 The third line of defense is specific reactions to disruption of homeostasis

Lymphocytes WBCs that circulate in blood and lymph 2 types T Cells B Cells Recognize foreign invaders

B Cells Foreign molecules called antigens are recognized by B Cell's receptors B cells release antiBodies which identify and attack specific foreign invaders

T Cells Similar to B cells – but do not secrete antibodies Identify and attack invaders It is T cells that are attacked by the AIDS virus

Antigen = foreign molecule Pathogen = foreign organism Quick Note Antigen = foreign molecule Pathogen = foreign organism Often used interchangeably WBCs may recognize an antigen that is a part of a pathogen

Once An Antigen Binds... Lymphocytes divide into 2 sets of cells Effector cells which fight the infection Memory cells which are long-lived and “remember” the antigen

Quick Review We have millions of lymphocytes When a single lymphocyte recognizes an antigen, it multiplies to attack the invader and remember it Creates a specific response

Primary vs. Secondary Immune Response It takes about 10-17 days to generate the maximum response to a foreign microbe and clear the antigens from the body During the wait time is when people feel ill If exposed to the same antigen, it takes only 2-7 days to clear the body, which is called the Secondary Immune Response More antibodies that are more specific are made due to memory cells This is called immunological memory

Self-Tolerance When lymphocytes are being made they are tested with molecules from the body Any T or B cell that reacts to the body is destroyed This, however, goes wrong in diseases like multiple sclerosis

Main Point #4 Specific immune responses consist of antibodies and T cells fighting off foreign antigens

Immune Responses The humoral response defends against extracellular antigens (in the blood) Formation of antibodies in blood The cell-mediated response defends against pathogens inside of cells Destruction of infected or cancerous cells

Helper T Cells Help stimulate both responses Important in recognizing antigens a second time It is these specific T cells that HIV and AIDS affect

Cell-Mediated Response Antigens bind to a T cell called a cytotoxic T cell It creates memory cells and active cytotoxic T cells Active Cytotoxic T cells lyse and burst infected and cancerous cells

Humoral Immunity Overview Antigens are recognized by B cells B cells give rise to plasma cells and memory B cells Plasma cells secrete antibodies Antibodies bind antigens and help the eliminate them

Main Point #5 Antibodies help fight viruses and bacteria outside of the cells in a number of different ways

Antibodies Proteins that can bind multiple antigens Helps disposal of pathogens in a number of ways

Neutralization Antibody binds and blocks activity of antigen i.e. an antibody can bind to the part of a virus that inserts the virus into cells

Opsonization Antibodies bind and make it easier for macrophages to digest pathogen

Agglutination Antibodies can clump bacteria or viruses together Antibodies have multiple attachment sites Makes it easier for phagocytes to digest

Review Barriers Inflammatory Response Immune Response Skin/mucus/lysozyme Inflammatory Response Basophils release histamine Swelling, non-specific WBCs Neutrophils, Monocytes (macrophages), eosinophils, natural killer cells Immune Response Lymphocytes attack specific antigens Humoral (B cells, antibodies) and Cell- mediated (T cells)

White Blood Cells (Leukocytes) Neutrophil – most common, phagocyte Monocyte – forms macrophage Eosinophils – Attacks larger parasites Basophils – Release histamine Lymphocyte – Recognition and attack of specific pathogens

Major Histocompatibility Complex (MHC) Molecules on cell surface that help the body distinguish self from non-self Cells can display “self” MHC molecules to avoid being attacked But a cancerous cell or a WBC that has ingested a foreign molecule can display a “non-self” molecule, so that it is attacked

The Immune System Makes Tissue Transplant Difficult It is difficult (but possible) to transfer tissues such as blood, skin or organs to new individuals The body recognizes foreign tissues Easier to use tissue from one's own body

Tissue Transplants The MHC recognizes foreign tissues Donors and recipients must be closely matched Twins and siblings are usually the closest matches

Blood Transfusions Blood types can be considered antigens Type A produces A antigens, B produces B antigens, O produces no antigens People with B or O blood types produces A antibodies People with O blood produce both antibodies (can't receive A or B blood)

Blood Transfusions Gone Wrong You cannot receive blood for which you have antibodies! If you’re type O, you produce A and B antibodies – you can only receive type O blood If you’re AB – you produce no antibodies – you can accept any blood (this oversimplifies things a bit, there is also the Rh factor and other blood antigens)

Allergies Leftover response to fighting worms? Allergens act as antigens, causing mast cells to over-release histamine Causes blood to flow to capillaries

Anaphylactic Shock When too much histamine is released blood pressure drops Too much blood flows out of the capillaries Epinephrine must be taken to counteract this effect

Multiple Sclerosis The immune system breaks down nervous tissue Usually gets worse and worse Not deadly, but debilitating No cure