1

Chapter 20

Defenses Against Disease:

The Immune System

2

Outline• Functions of the Immune System

– Definitions• Primary & Secondary Immune Organs• Nonspecific Defenses: Aid Immune System

– Barriers to Entry– Inflammatory Reaction– Complement System

• Specific Defenses: The Immune Response– B-lymphocytes: Antibody-Mediated Immunity– T-lymphocytes: Cell-Mediated Immunity

• Induced vs. Passive Immunity

3

Functions of The Immune System

• The immune system functions to defend the body against all attackers including viruses, bacteria, and cancer cells.

• Protects “self” from “non-self”.• Immunity is the ability to react to antigens so

that the body remains free of disease.– Disease is a state of homeostatic

imbalance.– Disease can be due to infection or failure

of the immune system.

4

Functions of The Immune System (Con’t)

• Definitions– Antigen: Piece or part of a foreign attacker

such as a piece of protein or cell membrane.

– Antibody: Special protein produced by the immune system to bind specifically to antigens. Antibody shape fits like a glove to the surface shape of the antigen. Helps to remove attacker from the body.

5

Primary Immune Organs• Immune system is network of organs, tissues,

cells, and cell produces.• Principal cells are the lymphocytes, aided and

assisted by neutrophils, macrophages.• Two types: B lymphocytes and T lymphocytes• Primary Immune Organs: Lymphatic organs

contain large numbers of lymphocytes.– Red Bone Marrow: Source of B & T

lymphocytes; B lymphocytes mature here; move to lymph nodes

– Thymus Gland: T lymphocytes move here from bone marrow; mature here; move to lymph nodes.

6

Secondary Immune Organs

• Secondary Immune Organs: Secondary lymphatic organs are places where lymphocytes encounter and bind with antigens.– Spleen.– Lymph nodes: In the lymphatic system– Tonsils: Lymphatic tissue at back of

mouth– Peyer’s patches: Lymphatic tissue in

intestines

7

Lymphatic Organs

8

Nonspecific Defenses: Aid Immune System

• Barriers to Entry.– Skin.

Oil gland secretions.– Ciliated cells and mucous membranes of

the respiratory tract.– Stomach.

Acid in stomach; pH 1-2.

9

Nonspecific Defenses: Aid Immune System

• Inflammatory Reaction.– Tissue damage causes tissue cells and

mast cells to release chemical mediators.Histamine and kinins.

Capillaries dilate and become more permeable.

Skin reddens and becomes warm. Proteins and fluids escape from

tissue. Swelling.

10

11

Nonspecific Defenses: Aid Immune System

• Inflammatory Reaction. Proteins and fluids escape from

tissue and cause swelling. Swelling stimulates free nerve

endings, causing the sensation of pain.

– Neutrophils and monocytes migrate to site of injury; engulf pathogens.

– Monocytes become macrophages; engulf pathogens; spit out antigens.

12

13

Nonspecific Defenses: Aid Immune System

• Inflammatory Reaction Movies

1. Rolling Leukocytes

2. Lymphocyte Homing

3. Chemotaxis of Neutrophils

4. Neutrophil Chase

14

Nonspecific Defenses: Aid Immune System

• Complement system: Group of proteins in blood that help to destroy pathogens.

• Complement proteins are activated when antibodies coat pathogens in the body.

• They form membrane attack complex that knocks holes in the membrane of pathogen.

• Complement coated pathogens also attract neutrophils and macrophages.

15

Complement System

16

Specific Defenses: The Immune Response

• Specific defenses respond to antigens.– Lymphocytes recognize an antigen due to

antigen receptors whose shape allows them to combine with a specific antigen.

Immunity is primarily the result of the action of B lymphocytes and T lymphocytes.

17

Specific Defenses: The Immune Response

– B-lymphocytes and antibody-mediated immunity.

Main end products: Antibodies and memory B-lymphocytes.

Antibodies bind to pathogens; they help complement to work; help neutrophils and macrophages find and engulf them.

18

19

Specific Defenses: The Immune Response

• B-lymphocyte Review– Provide antibody-mediated immunity against

bacteria.– Produced and mature in bone marrow.– Reside in spleen and lymph nodes.– Circulate in blood and lymph.– Directly recognize antigen and then undergo

clonal selection.– Clonal expansion produces antibody-secreting

plasma cells and memory B cells.

20

Structure of most common antibody: IgG

21

Specific Defenses: The Immune Response

– T-lymphocytes and cell-mediated immunity.

Main end products: Cytotoxic T-lymphocytes and memory T-lymphocytes.

Cytotoxic T-lymphocytes bind antigen-bearing, pathogen infected cells and destroy them; they also attack cancer cells and destroy them.

22

23

24

Specific Defenses: The Immune Response

• T-lymphocyte Review– Provide cell-mediated immunity.– Produced in bone marrow, mature in

thymus.– Antigen must be presented in groove of

HLA molecule.– Cytotoxic T cells destroy nonself protein-

bearing cells.– Helper T cells secrete cytokines that

control the immune response.

25

Induced Immunity

• Active Immunity.– Immunization involves use of vaccines.

Contain an antigen to which the immune system responds.

Primary response. Secondary (booster) response.

– Dependent upon the presence of memory B and T cells capable of responding to lower antigen doses.

26

Passive Immunity

• Passive immunity occurs when an individual is given prepared antibodies.– Temporary.

No memory cells.

27

Immunity Side Effects

• Allergies.– Hypersensitivities to substances

(allergens) that would ordinarily not harm to the body.

Immediate allergic responses are caused by IgE.

Delayed allergic responses are initiated by memory T cells at the site of allergen contact.

28

Tissue Rejection and Autoimmune Diseases

• Tissue rejection occurs because antibodies and cytotoxic T cells begin to destroy foreign tissues in the body.– Immune system working correctly.

• Autoimmune diseases occur when antibodies mistakenly attack the body’s own cells as if they bear foreign antigens.– Immune system working incorrectly.

29

Need to Know1. Functions of Immune System

A. Defense against “non-self”.1. Bacteria2. Viruses3. Cancer Cells

B. Generate Immunity1. To remain free of disease.

C. Definitions1. Antigen: Part or piece of foreign attacker,

usually a piece of protein or cell membrane2. Antibody: Special protein made to fit

antigen like a glove

30

Need to Know (Con’t)2. Nonspecific Defenses: Aid Immune Response

A. Inflammatory Reaction1. Results: Neutrophils, macrophages engulf and kill

pathogens and spit out antigens

3. Specific Defenses: The Immune Response

A. B-lymphocytes & antibody mediated immunity1. Main end product: Antibodies & memory B-lymphocytes

2. Antibodies help macrophages and complement to remove pathogens

B. T-lymphocytes & cell mediated immunity1. Main end product: Cytotoxic T-lymphocytes & memory T-

lymphocytes

2. Attack and kill antigen-bearing pathogen infected cells & cancer cells

31

Need to Know (Con’t)

4. Induced vs. Passive ImmunityA. Induced (Active) Immunity: Addition of

vaccine to body stimulates immune system; helps maintain memory cells

B. Passive Immunity: Antibodies given to person; temporary; no memory cells

5. Complement SystemA. Works with antibodies to help kill

pathogens like bacteriaB. Binds and generates holes in bacteria

32

Need to Know (Con’t)

6. Primary & Secondary Immune OrgansA. Primary

1. Red Bone Marrow: both B & T-lymphocytes

2. Thymus Gland: T-lymphocytes mature here

B. Secondary: Lymphatic tissue throughout the body

1. Spleen2. Lymph nodes3. Tonsils4. Peyer’s Patches