1. The Immune System

2. Host and Invaders
Pathogens are disease-causing agents and can be found on almost any surface we touch
Host- organism invaded
Pathogens- organism that invades, include viruses, bacteria, and protists, fungi and multicellular animals

3. First Line of Defense: Innate Immune Response
Protects against infection with no specificity
Non-specific or innate immune response:
Note: the book uses the term “innate immune response” incorrectly. The innate immune response is both external and internal, not just internal?!

4. Figure 32.2 An Overview of the Immune System in Animals
Immune Response
Innate: Non-Specific
Adaptive: Specific
External
Internal
Physical
Chemical
Phagocytosis
Inflammation
Antibody- mediated
Cell-mediated
Figure 32.2 An Overview of the Immune System in Animals

5. External Innate Response
Includes the:
Skin
Mucus
Cilia
Probiotic bacteria
Tears
Immune Response
Innate: Non-Specific
Adaptive: Specific
External
Internal
Physical
Chemical
Phagocytosis
Inflammation
Antibody- mediated
Cell-mediated

6. External Innate Response: Physical and Chemical Barriers
Physical and chemical barriers are the first line of defense against invading pathogens
Physical barriers act to block entry to the body
Chemical defenses, such as enzymes, work to keep the invaders from attaching to or growing on body surfaces

7. External Innate Response: Physical and Chemical Barriers
Linings that separate the inside from the outside in the lungs, digestive system, reproductive system, and skin keep most pathogens out
Acidic pH of the skin
Salty secretions from skin glands
Defensins: small chains of amino acids that can destroy many types of bacteria and some viruses

8. Internal Innate Response
Once a pathogen passes the external defense systems, the body must distinguish foreign invaders (nonself) from our own cells
As soon as the body detects cells or molecules that do not belong, a nonspecific response is deployed taking measures to eliminate the pathogens and nonself substances
red blood cells and white blood cells including: lymphocytes, a monocyte, a neutrophil, and many small disc-shaped platelets

9. Internal Innate Response
Includes:
Inflammation
Mast cells (in connective tissue and in the mucous membranes)
Phagocytes (eating cells)
Neutrophils (release toxins for bacteria and fungus)

10. Internal Innate Response
The defense cells, proteins, and other molecules of the innate immune system are the second line of defense and fight an invading organism, virus, or other substance perceived as non-self
The innate immune system does not provide long-lasting protection against pathogens
It is found in both invertebrates and vertebrates

11. Internal Innate Response: Phagocytes
White blood cells called phagocytes, which include macrophages and neutrophils, destroy invading cellular organisms by engulfing their target in a process called phagocytosis
The engulfed pathogen is confined to a membrane-enclosed compartment, where it is chemically broken down or walled off from other cells
Individual phagocytes die when they are full of pathogens
Macrophages are relatively large and may take an hour or more to engulf a pathogen.
Neutrophils—the most abundant type of white blood cell—attack pathogens with antimicrobial chemicals and destroy bacteria by engulfment

12. Innate Response: Inflammation
Shields an injury site from potential pathogens
Cleans up damaged tissues and prevents entry or spread of a pathogen
Direct injury or activation by chemical signals stimulates mast cells to release histamine and other alarm signals, including cytokines

13. Innate Response: Inflammation
Histamine increases blood flow by dilating blood vessels and makes the capillary walls more porous to allow other immune cells to infiltrate the area
Histamines can also irritate nerve endings, leading to itching or pain

14. Innate Response: Blood Clots
Responsible for clotting the blood to close a wound
Clotting reduces blood loss and restores the integrity of external defense barriers
Platelets are sticky cell fragments that circulate in the blood and interlink with the clotting proteins to form a gel-like mesh that traps blood cells

15. Innate Response: Fever
Cytokines and histamines trigger the release of prostaglandins to stimulate the hypothalamus and raise the body temperature, resulting in a fever
Fevers are beneficial because they limit the growth of many pathogens, enhance phagocytosis, and speed the repair of damaged tissues
Cytokine

16. Innate Response: Complement Proteins
Complement proteins work by binding to the invading cells and destroy them by creating holes in their plasma membranes
Complement proteins “flag” invaders to help phagocytes and white blood cells identify them

17. Innate Response: Direct Attack
Viruses are a bit different than other pathogens
Cells infected by viruses release interferon, which attaches to the plasma membranes of nearby cells, interfering with the ability of the virus to enter and infect them
Describe viruses!!!!!!!!!!!!!!!!!!

18. Innate Response: Direct Attack
Interferon also signals natural killer (NK) cells to destroy any cell whose plasma membrane is marked with foreign proteins NK
Describe viruses!!!!!!!!!!!!!!!!!!
Cancer cell

19. Adaptive Immune Response
If the innate immune responses fail vertebrates have a layer of defense known as the adaptive immune system:
response is highly specific for a particular pathogen
slower than the innate immune systems
considered the most sophisticated and effective of animal defense systems

20. Adaptive Immune Response
The adaptive immune system has two features:
Antibody-mediated immunity: uses antipathogen proteins called antibodies
Cell-mediated immunity: destroys cells harboring pathogens and other substances that are sensed as foreign by the body
Immune Response
Innate: Non-Specific
Adaptive: Specific
External
Internal
Physical
Chemical
Phagocytosis
Inflammation
Antibody- mediated
Cell-mediated

21. The Lymphatic System Supports Immunity
Defensive proteins and white blood cells are collected, along with the interstitial fluid, in the lymphatic ducts, a network of tubes that returns the interstitial fluid to the circulatory system
Lymph nodes are located along the lymphatic ducts and contain large numbers of white blood cells, such as lymphocytes, that trap bacteria, viruses, and foreign proteins
Lymphatic ducts, lymph nodes, and organs such as the spleen make up the lymphatic system

22. B and T Lymphocytes Recognize Pathogens
B lymphocytes mature in the bone marrow, while T lymphocytes migrate from the bone to mature in the thymus
Large numbers of mature B cells and T cells are found in the lymph nodes and other organs of the lymphatic system

23. B and T Lymphocytes Recognize Pathogens
B or T cells specialize in recognizing specific antigens, one or more molecules displayed on the surface of a particular pathogen or foreign substance
Hemagglutinin and neuraminidase both antigens on influenza virus

24. B and T Lymphocytes Recognize Pathogens
Each lymphocyte is individually specialized to recognize and bind with only its corresponding antigen
Once a specific antigen has been detected, each activated lymphocyte divides rapidly to make many identical copies in a process called clonal selection

25. B Cells Produce Antibodies
B cells produce antibodies, proteins that specifically bind to and tag pathogenic cells
This deploys the antibody-mediated immunity, which specifically targets the antigen on an invading pathogen

26. B Cells Produce Antibodies
Antibodies increase the ease with which macrophages and neutrophils can bind to and destroy invaders as well as bind to and neutralize small foreign molecules, such as toxins

27. T Cells Target Infected or Abnormal Cells
Immunity involving the action of T cells is called cell-mediated immunity because the T cell receptor proteins bind to their target antigens, becoming attached to the target cell
Antigen-presenting cells are phagocytes that specialize in presenting the antigens from ingested pathogens on the surface of the cell.

28. T Cells Target Infected or Abnormal Cells
Helper T cells act as guides for other cells in the immune system
Cytotoxic T cells destroy the body’s own cells that are damaged, exhibit the cell surface signature of a cancer, or have been infected by viruses

29. The First Infection Produces a Slower, Milder Immune Response
The first exposure to a particular antigen sets into motion the primary immune response of adaptive immunity
A majority of the cloned lymphocytes become effector cells, cells that are ready to engage the antigen-bearing pathogen, tumor cell, or foreign substance
A small number of the cloned lymphocytes become memory cells, which are held in reserve to provide a rapid response to a repeat invasion by the same foreign particle

30. Subsequent Exposures Provoke a Faster, Stronger Response
The immune cells’ memory of our own specific response to a pathogen is what enables us to become immune to further attacks by the same strain in the future
This system has immune memory that remembers a first encounter with a specific strain of pathogen and mobilizes a quick, targeted, response to a repeat infection by the same strain

31. Immunity May Be Active
Active immunity to a particular pathogen occurs when the antibodies are produced by our own bodies
We can also acquire active immunity when we receive a vaccine consisting of antigen-containing preparations
Booster shots are repeat vaccinations that restore immunity by raising antibody concentrations and memory B cell numbers through fresh exposure to the antigens

32. Immunity May Be Passive
Passive immunity occurs when we receive antibodies that were not made by our own bodies
A nursing baby receives passive immunity to a broad range of potential pathogens from its mother
Passive immunity produces no memory cells and therefore wears off over time
Passive immunity can also be delivered artificially, by injection of a concentrated dose of premade antibodies