1. Immune System
Chapter 43
AP/IB Biology

2. Importance of the Immune System
Defends against foreign invaders (bacteria, fungi, protists, parasites, etc.)
Destroys abnormal body cells

3. Types of Defense Innate Defenses – non- discriminating mechanisms
1st Line – Skin and mucous membranes – prevent entry into body; trap foreign bodies
Lysozyme – digests microbial cell walls

4. 2nd Line
Phagocytic cells – engulf and destroy foreign bodies

5. Inflammatory Response
Localized response in a damaged area
Histamine – released by body cells
Blood flow increases to that area
Permeability of capillaries increases
Phagocytic cells arrive

6. Natural Killer (NK) cells – recognize infected cells and destroy them
Interferons – secreted by virus infected cells (“save yourself” message)
Diffuse to neighboring cells and cause them to release other chemicals that inhibit viral production
Natural Killer (NK) cells – recognize infected cells and destroy them

7. Specific Defense – 3rd Line
Selective with what is foreign
Foreign identified by antigens, molecules found on surfaces that elicit a response by lymphocytes
Circulate throughout blood and lymph; concentrated in spleen, lymph nodes and other lymphatic tissue

8. Lymphocytes Pass antigen receptors (~100,000) on the plasma membrane
Receptors are antigen specific (only 1)
Body constantly produces varieties of two types of lymphocytes

9. B Lymphocytes
B Cells
Originate and mature in stem cells of bone marrow
When activated, some can produce antigen specific antibodies – proteins that are attracted to specific antigens
Some can become long living memory B cells – able to produce antibodies later in time

10. T Lymphocytes
T Cells
Produced in stem cells of bone marrow and mature in the thymus
Types include
Helper T Cells – recognizes antigen-presenting cells and stimulate B cells and…
Cytotoxic T Cells – involved in the destruction of tumor cells, virus- infected cells, or other damaged cells
Memory T Cells – long-living cells that can recognize abnormal cells later in time

11. Recognizing Self from Non-Self
The immune system has the ability to recognize what is foreign and what should be present
On surface of membranes are molecules that generate a membrane fingerprint (major histocompatibility complex – MHC)
Recognized by T cells
Antigen fragments are presented in the MHC so that T cells may recognize them

12. Clonal Selection
Immune system generates a wide variety of different B and T cells (different antigen receptors)
Only B or T cell with the exact antigen receptor is selected to divide and differentiate
Effector cells – short lived; become the cells that fight
Memory cells – long lived cells that remain

13. Humoral Immunity Bacteria and viruses Antigen enters (1st exposure)
Free floating antigens activate selected B cells
Plasma cells secrete antibodies
Memory cells are generated
If antigens consumed by macrophage
Antigen is presented to Helper T cell can also activate selected B cells

14. Effect of Antibodies

16. Cell Mediated Immunity
Bacteria, viruses, fungi, protists
Antigen enters (1st exposure)
Macrophage presents antigen to Helper T cell or displayed by an infected cell
Cytotoxic T cells selected and stimulated
Active cytotoxic T cells generated (lyse cells)
Memory T cells generated

18. Primary vs. Secondary Immune Response
Primary is response from the initial exposure to the antigen
10-17 days required to generate effector cells
Symptoms seen
Secondary is the response from a following exposure
Memory cells react quickly (2-7 days)
Slight to no symptoms

19. Acquiring Immunity Active Immunity Immunization/Vaccination
Natural exposure to an antigen
Immunization/Vaccination
Exposure to inactivated, weakened, or parts of antigens (primary immune response stimulated with little to no symptoms)
Passive Immunity
Antibodies passed from person to person (breast milk to child)

20. Problems and Concerns
Limits to blood transfusions and tissue transplants
ABO Blood Group
MHC different, resulting in immune responses
Require immune suppressing drugs

21. Abnormal Immune Function
Allergies – exaggerated immune response to harmless antigens; results in large amounts of histamine to be released (on a second exposure to allergen)

22. Autoimmune Disease – immune system attacks certain molecules in the body that should be recognized as self (rheumatoid arthritis, lupus)
Immunodeficiency Disease – aspects of the immune system fail to function
Sever Combined Immunodeficiency Syndrome (SCID) – both branches do not work

23. Acquired Diseases Human Immunodeficiency Virus (HIV)
Infect cells with the CD4 marker (primarily helper T cells)
Is a retrovirus – uses reverse transcriptase to make DNA from RNA; DNA incorporated into host DNA and new viruses are made