1. Chapter 43 Biology – Campbell • Reece
The Immune System
Chapter 43
Biology – Campbell • Reece

2. Nonspecific Defenses First line of defense:
Unbroken skin (minute cuts will allow the bacteria or virus through)
Mucous membranes (line the digestive, respiratory and genitourinary tracts)
Chemical secretions of skin and mucous membranes
Lysozyme – digests the cell walls of many bacteria

3. Nonspecific Defenses Second line of defense:
Phagocytic white blood cells (neutrophils, macrophages, eosinophils) – ingest the invading organism
Antimicrobial proteins – either attack directly or inhibit reproduction
Inflammatory Response – blood vessels dilate to increase blood flow to the area, histamine is released, blood clotting begins, phagocytes are sent

4. Inflammatory Response

5. Specific Immunity Third line of defense
Lymphocytes are the key cells of the immune system
B lymphocytes (B cells) – develops in the bone marrow
T lymphocytes (T cells) – differentiate under the influence of the thymus
Primary immune response – attack by the lymphocytes the first time the body is exposed

6. Specificity of Lymphocytes
Antigen – a foreign molecule that elicits a specific response
Antibodies – proteins that recognize specific antigens
Antigen receptors – receptors on the B and T cells that bind certain antigens

7. Clonal Selection
When the antigen is recognized, the proper lymphocyte is selected and cloned
Two forms of clones are produced:
Effector (plasma) cells – short-lived cells that secrete the specific antibody
Memory cells – long-lived cells bearing receptors for the same antigen

8. Clonal Selection

9. Secondary Immune Response
When the individual is exposed to the same antigen later, the response is much faster, of greater magnitude, and more prolonged
The memory cells recognize the antigen and produce a response more quickly

10. Distinguishing self from nonself
The body will destroy any lymphocytes that bear receptors for molecules already present in the body
Failure to do this leads to autoimmune diseases (such as multiple sclerosis)
Cells have special glycoproteins on their surface called MHC (major histocompatibility complex) or HLA (human leukocyte antigens) which mark body cells as “self”

11. Distinguishing self from nonself
Two types – Class I MHC molecules and Class II MHC molecules
Two types of T cells that responds to each kind of MHC molecule
Cytotoxic T cells – bind to cells with class I MHC molecules
Helper T cells – bind to cells with class II MHC molecules
Triggers an immune response

12. Cytotoxic and Helper T cells

13. Cell-mediated Response
Class I MHC molecules capture fragments of the infecting agent and transport them to the surface of the cell
These foreign particles are “presented” and a cytotoxic T cell is activated
The cytotoxic T cell kills the infected cell
The pathogen is now exposed to the antibodies that will destroy it

14. Humoral Response Initiated when B cells bind with specific antigens
B cells are activated by Interleukin-2 and other cytokines secreted from the Helper T cells
The B cells then generate the plasma cells that produce antibodies to destroy the pathogen

15. Antibody Structure & Function
The antigen has several different epitopes or locations where an antibody can bind
A single antigen may bind several antibodies

16. Antibody Structure & Function
Antibodies are also called immunoglobulins
Each molecule has four polypeptide chains: two identical heavy chains and two identical light chains, joined by disulfide bridges to form a Y-shaped molecule
Variable regions at the ends of the light and heavy chains provide the specific binding site

17. Antibody Structure & Function

18. Immunoglobulins

19. Antibody-Mediated Disposal of Antigen
Neutralization – the antibody binds to and blocks the activity of the antigen
Opsonization – the bound antibodies enhance macrophage attachment to the pathogen
Agglutination – clumping of the pathogen
Complement fixation – activation of the complement system that leads to cell lysis

20. Antibody-Mediated Disposal of Antigen