Nonspecific Host Defense Mechanisms

1. Nonspecific Host Defense Mechanisms

2. Host Defense Mechanisms • Ways in which the body protects itself from pathogens • There are 3 lines of defense. • The first two lines of defense are nonspecific. • The body’s way of destroying all foreign substances that enter including pathogens • The third line of defense is specific. • Antibodies are produced in response to an antigen.

3. First Line of Defense • Skin • Serves as a physical barrier to pathogens • Few microbes can penetrate intact skin • Mucous Membranes • Although they are only one cell layer thick, they are a physical barrier to pathogens. • Goblet cells produce mucus that entrap pathogens and prevent them from causing infection. www.nlm.nih.gov www.facilities.unt.edu

4. What are some chemical and cellular examples for the first line of defense? Regarding the skin? Mucous membrane cells? Digestive tract?

5. First Line of Defense • Microbial Antagonism • When the presence of the normal flora prevents colonization of pathogens • This may happen because of: • Competition for colonization sites • Competition for nutrients • Production of substances that kill other bacteria

6. Second Line of Defense • If pathogens get passed the first line of defense, they are usually destroyed by the second line of defense. • These involve chemical and cellular reactions by the body, which result in: • Fever • Production of interferons • Activation of the complement system • Inflammation • Chemotaxis • Phagocytosis

7. Transferrin • A protein that is made in the liver and has a high affinity for iron. • Its role in the body is to store and deliver iron to host cells. • During an infection, its production is greatly increased in the body. • Binds to the iron present so that other microbes cannot use this essential nutrient

8. www.mcmua.com Fever • Increase in normal body temperature (above 100°F) • Pyrogens stimulate the production of a fever. • May originate from outside (i.e. pathogens) or inside the body (i.e. Interleukin 1 – IL-1) • Helps body in following ways: • Stimulates white blood cells (leukocytes) to go and destroy invaders • Reduces free plasma iron • Induces the production of IL-1 that results in the activation of leukocytes in the immune response

9. Interferons • Small, antiviral proteins produced by virus-infected cells • Attach to other host cells to prevent further viral replication • “interfere” with viral replication • Limits spread of disease so that other responses may help fight pathogens

10. The Complement System • Involves about 30 proteins found in normal blood plasma that interact together in response to the presence of a foreign substance • Results in a complex stepwise reaction called the complement cascade • Which results in: • Attraction of phagocytes to sites where they are needed • Activation of leukocytes • Lysis of bacteria and other foreign cells • Increased phagocytosis

11. Acute-Phase Proteins • Proteins found in blood plasma that greatly increase in response to infection, inflammation, and tissue injury • Help to prevent infection and promote tissue repair • Example : C-reactive protein • Which is used as a marker for inflammation

12. Cytokines • Chemical mediators that are released from many different types of cells in the human body. • Help cells to communicate with each other • Aid in communication within the immune system and between the immune system and other systems • If another type of cell has the right receptors, it can recognize the presence of cytokines.

13. Inflammation • Occurs as a result of an injury, irritation, microbial invasion, or bacterial toxin • 4 signs of inflammation: • Redness, heat, swelling, pain • Results in a cascade of events that work to: • Localize an infection • Prevent the spread of microbial invaders • Neutralize any toxins being produced at the site • Aid in the repair of damaged tissue

14. www.georgiapainphysicians.com www.georgiapainphysicians.com Inflammation • Vasodilation (increase in the diameter of capillaries), which increases blood flow to the site • Results in redness and heat • Increased permeability of capillaries, allowing the escape of plasma and plasma proteins • Causes edema (swelling) • Exit of leukocytes from the capillaries and their accumulation at the site of injury • Injury or infection attracts chemotactic agents which in turn attract leukocytes

15. Phagocytosis • The process by which phagocytes surround and engulf foreign material • Phagocytes – phagocytic white blood cells www.nytimes.com

16. Cellular Elements of the Blood • Erythrocytes (red blood cells) • Thrombocytes (platelets) • Leukocytes (white blood cells) • Granulocytes • Basophils • Eosinophils - Phagocytic • Neutrophils - Phagocytic • Monocytes/Macrophages - Phagocytic • Lymphocytes • B cells • T cells • Natural killer cells www.nytimes.com

17. 4 Steps in Phagocytosis • 1. Chemotaxis • Phagocytes are attracted by chemotactic agents to the site where they are needed. • 2. Attachment • Phagocyte attaches to an object. • 3. Ingestion • Pseudopodia surround the object, and it is taken into the cell. • 4. Digestion • The object is broken down and dissolved by digestive enzymes and other mechanisms.

18. Phagocytosis www.biolcell.org

19. The End