Earth is full of microscopic invaders that can wage war in your body. Infectious diseases are caused by microorganisms; viruses, bacteria, fungi, protists, or parasites. How do you battle against such invaders? In the next few lessons you will learn about how your body wages war against the tiny invaders!

or water. How do you defeat them every day? Immune System Pathogens cause disease and spread through from one person to the next by coughing, sneezing, bodily fluids, physical contact, contaminated food, or water. How do you defeat them every day? There are two types of defense mechanisms Non-specific Fights against any pathogens Specific Fights against specific Pathogens and invaders There are 3 lines of defense. 1st line of defense 2nd line of defense 3rd line of defense

Holding the front line Non specific immune response Your skin is the 1st line of defense against any invaders called pathogens.

1st Line of Defense Also includes: Inner skin called epithelial lining, has mucous membranes that release mucus that contains lysozyme an antimicrobial substance. Your respiratory tract is lined with cilia to move trapped invaders up and out of the body, keeping them from lodging in the lungs. bacteria mucus cilia Section of respiratory tract

If the barriers have been breached? Second Line of Defense Phagocytic Cells Natural Killer Cells Interferons Complement System Interferon Can not infect now Cascade of chemical reactions

Phagocytic Cells Leucocytes or White Blood Cells Neutrophils Eosinophils Neutrophils Main defense against large parasitic invaders Cells damaged by invaders release chemical signals that attract neutrophils from blood to site location of tissue cells being invaded. Once they engulf and destroy microbe they self destruct. Average life span is only a few days. Monocytes Circulates in blood for a few hours the migrates to tissues to become macrophages. Macrophages Largest and longest lived. Long pseudopodia extend to pull invaders in for digestion. If pathogens get last the 1st line of defense, then the non-specific mechanism is mainly phagocytosis which is the ingestion of invading organisms.

2nd line of Defense….the others… Antimicrobial Proteins Natural Killer Cells Destroy body cells that have become infected by causing them to lyse. Destroy abnormal body cells that could or have become cancerous. Interferon Proteins secreted by virus-infected cells to diffuse into neighboring cells. Induces production of antiviral proteins that will inhibit viral reproduction in the neighboring cells protecting them from viral invasion Complement System A set of about 20 serum proteins that carry out a cascade of chemical reactions eventually leading to lysis of invading microbes. * Also found in specific system

The barrier is breached…..invaders have entered the skin… A series of events occur when an invader enters the body. The Second line of defense kicks in with the Inflammatory Response Inflammatory Response Mast cells in tissue produce histamines; Histamines cause vasodilation; the capillaries dilate and get larger so large phagocytes, macrophages can move out of the capillaries and into the infected tissue. Often fever accompanies the response, it slows growth of invader and optimizes environment for phagocytes. A slight fever aids in the immune response because it increases phagocyte proliferation and metabolism, increasing the response to the invader. Swelling begins Redness begins Fever begins

Review What do nonspecific defenses respond to? What is the difference between the 1st and 2nd line of Defense? What causes infectious disease? How does infectious disease spread? How does the first line of defense protect you from the pathogens? What do Phagocytic cells do?

the 3rd line of Defense kicks in. The beauty of the Immune System MHC Major Histocompatibility Complex Molecules These molecules are markers on the cell surface that distinguish cells as “self” cells. No two people have the same MHC markers except for identical twins. There are two classes of MHC. Class I Class II Found on almost every body cell. Specialized cells Macrophage B-cells Activated T-cells When a cell that has a foreign marker or antigen become present in the body the 3rd line of Defense kicks in.

The 3rd line of Defense Most invaders carry antigens on their cell membrane. Antigens are antibody generating molecules. Our body recognizes antigen cells as not “self” cells, and begins to make antibodies against the invaders. The antibodies are very specific to the antigens. The 3rd line of defense is the specific mechanism of the immune system, two responses occurring simultaneously; cell-mediated and humoral Lymphocytes are produced from Lymph System; T-cell and B-cell

Specific Immune Responses 1. Macrophage engulfs invader and displays the antigen on cell surface. Now called a Antigen Presenting Cell 2.A helper T-cell with the receptor matching the antigen hooks up with the macrophage 3. Macrophage releases a cytokine, Interleukin-1 which increases the production of more helper T-cells with the same receptor and enhances binding between MHC and T-cell receptor. 4. T-cell release more cytokines and Interleuking-2 which stimulates mitotic division of helper T-cells, production of cytotoxic T-cells, production of memory helper T-cells and activation of B-cells Humoral Response 5 a. Cell-mediated Response The next slide will display a visual representation of this information. 5 b. B-cell that were activated change to either plasma cells or memory cells 6. Plasma cells (specialized cells) make complementary antibodies to bind with viral antigen 6. Memory cells are for long term protection. Remember and attack repeated infections. Cytotoxic T-cells Attach and destroy infected body cells release perforins which are proteins to form holes in the cell membranes of infected body cells causing cytolysis

Here is how it works… Macrophage 1. 5 b. 2. 4. helper T-cell B-cells 3. IL-2 and other cytokines viral antigen IL-1 virus helper T-cells 5 a. Memory helper T-cells 6. Plasma cells B-cell Memory cells Cytotoxic T-cells This is a visual representation of the previous slide. Antibodies Cytotoxic T-cell attacks Infected body cells. Antibodies attack viruses or pathogens act as signal flags to tell immune system to destroy them.

Pathogens Although not all diseases are caused by pathogens, it is important to learn some of the invaders that attack the human body and elicit an immune response. Bacteria Protozoan Parasites Viruses Fungus/Yeast Examples: Athletes foot Thrush Examples: Giardia Acanthomeoba Examples: Rhinovirus, Adenovirus, Rotavirus Bacillis, cocci, spiral structures. Examples: E.coli, Spirochete

Review What are the functions of the immune system’s specific defenses? How does the immune system recognize the cells and proteins that belong in the body as “self”? How does the body defend against infection? What is a pathogen? How do you think pathogens can get inside the body? What are the body’s specific defenses against pathogens? How do antibodies help the immune system? How do memory cells help protect for future infection?

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