Chapter 15 The Adaptive Immune Response

Question 1

Adaptive Immune Response

Answer 1

• Can be acquired either naturally or artificially
• Natural adaptive immunity: an organism or toxin enters the body and promotes an immune response
• Artificial adaptive immunity: results from immunization with a vaccine
• Both types are specific and have memory

Question 2

Specific Immune Response

Answer 2

• Immune response protects against one pathogen
• Does not protect against other pathogens
• Only exception is when two pathogens are very closely related
• Example: Smallpox or Cowpox

Question 3

Memory Immune Response

Answer 3

• Results in a much stronger response upon re-exposure

- Long term immunity - possibly for life

Question 4

Overview of Adaptive Immunity

Answer 4

• Involves two general responses that respond against antigens
  Molecules that interact specifically with the adaptive immune system and elicit an adaptive response

Question 5

Exogenous Antigens

Answer 5

Come from outside

- Example: Bacteria, Viruses, Toxins

Question 6

Endogenous Antigens

Answer 6

Generated inside a body cell

Question 7

Antibody Mediated Response (Humoral Response)

Answer 7

B cells

• Detect exogenous antigens and proliferate to form plasm cells
• Produce small protective molecules - antibodies (Ab)
• Bind to the surface of bacteria, viruses, toxins, etc.

Question 8

Cell Mediated Response

Answer 8

Helper T cells (TH)
- Direct and assist adaptive immunity and upregulate innate immunity
Cytotoxic T cells (Tc)
- Destroys abnormal body cells
- Example: Cells infected by viruses, and cancer cells

Question 9

Antigen - Antibody Generator

Answer 9

• Any molecule that induces antibody production, or binds to a specific receptor on a B or T cell
• Each antibody recognizes only a small part of the antigen called an epitope (antigenic determinant)
• A foreign particle (like a bacterial cell) has several antigens, and a vast array of potential epitopes
• Some antigens are more immunogenic than others - Ex. Proteins often elicit a strong immune response

Question 10

The Nature of Antibodies (Immunoglobulins)

Answer 10

• Y shaped proteins that bind to antigens in a very specific manner
  Like a “Lock and Key”
  Only an antigen with the correct epitope will be bound
• Each antibody binds to one and only one antigen

Question 11

Antibody Structure

Answer 11

• Each consists of 4 polypeptides - 2 light chains, and 2 heavy chains, and has 2 general parts:
  1) Two identical arms - Fab region (variable fragment)
• Each with an identical antigen binding site specific for one epitope
  2) One Stem - Fc region (constant fragment)
• Binds to complement proteins, phagocytes, etc, allowing the antibody to trigger other components of immunity

Question 12

6 Protective Functions of Antibodies

Answer 12

1) Cross-linking (agglutination)
2) Neutralization
3) Complement Activation
4) Opsonization
5) Ab Dependent Cytotoxicity
6) Immobilization and Prevention of Adherence

Question 13

Cross-linking (Agglutination)

Answer 13

• Antigens get stuck together

- Reduces number of infectious units to be dealt with

Question 14

Neutralization

Answer 14

• Ab binds to and inactivates toxins, bacteria, viruses

- Blocks attachment sites

Question 15

Complment Activation

Answer 15

• Ab binds bacteria - acts as starting point for complement pathway
• MAC attack

Question 16

Opsonization

Answer 16

Ab flags down phagocytic cells - to engulf and destroy the antigen

Question 17

Ab Dependent Cytotoxicity

Answer 17

Ab flags down immune system cells to destroy abnormal or infected body cells

Question 18

Immobilization and Prevention of Adherence

Answer 18

• Ab binds to flagella to stop pathogen from moving

- To pili to stop bacteria from colonizing

Question 19

5 Classes of Antibodies

Answer 19

1) IgG - Immunoglobulin G
2) IgM - Immunoglobulin M
3) IgA - Immunoglobulin A
4) IgD
5) IgE

Question 20

IgG - Immunoglobulin G

Answer 20

• Most abundant
• Binds to antigen very strongly
• Found in the blood - but can also enter tissues in regions of inflammation
  Can cross placenta - confers passive immunity to fetus

Question 21

IgM - Immunoglobulin M

Answer 21

• Consists of 5 units of Ab - a pentamer
• Does not move as freely as IgG - IgM stays in the blood
  Often attached to surface of B cells
  -First Ab produced upon infection
• Very good at cross-linking antigens

Question 22

IgA - Immunoglobulin A

Answer 22

• Consists of 2 units of Ab - a dimer
• Also known as secretory Ab
  Found in body secretions - saliva, mucous, tears, milk
• Functions to protect mucosal surfaces
  Protects gastrointestinal tract of newborns

Question 23

IgD

Answer 23

Function unknown

Question 24

IgE

Answer 24

• Found on the surface of certain immune system cells
• Mast cells and Basophils
• When it binds to antigens - the cell release histamine
  Attracts complement and phagocytes to the area.
  Histamine is responsible for allergy symptoms.

Question 25

B- lymphocytes (Cell of the Adaptive Immune System)

Answer 25

B cells - Antibody producing cells - Involved in humoral immune response

Question 26

T - lymphocytes (Cell of the Adaptive Immune System)

Answer 26

Helper T cells (Th cells) -Help B and Tc cells prepare for an immune response Cytotoxic T cells (Tc cells) -Destroy abnormal body cells - Ex. Cells infected by viruses and cancer cells

Question 27

Antigen Presenting Cells (APC)

Answer 27

Macrophages, B cells, dendritic cells a) Foreign material (ex. bacterial cell) is engulfed by APC b) Antigen is processes and presented to T cells along with self antigens - Self antigens - part of major histocompatibility complex (MHC) - Check to prevent destruction of our own cells by mistake c) T cells become activated against the foreign material

Question 28

The B-Cells Response: Humoral Immunity

Answer 28

- Each naive B cell carries Ig for one epitope on its surface - Circulates in blood, and gather in lymphoid organs

Question 29

If it encounters its specific epitope it will become activated

Answer 29

- B cell receptor binds to the epitope on the antigen - Clonal Selection - Antigen is phagocytized - Antigen is digested into small fragments - Small fragments are presented on surface along with MHC class II to T-helper cells (Th) - If a Th recognizes the fragment as foreign, it activates the B cell to multiply and differentiate - B cell undergoes clonal expansion

Question 30

Clonal Expansion

Answer 30

The activated B cell divides and differentiates into: 1) Plasma Cells 2) Memory B cells

Question 31

Plasma Cells

Answer 31

- Ab producing cells | - Short life span, produce a lot of Ab

Question 32

Memory B cells

Answer 32

- Long living:20-30 years - Circulate in blood - If it encounters Ag again it will quickly multiply and change into Ab producing plasma cells

Question 33

Primary Response (Immunologic Memory)

Answer 33

- B cells produce low levels of Ab - Slow process - takes 7-14 days - IgM first, followed by IgG and IgA - Major outcome: memory is built for the antigen

Question 34

Secondary Response (Immunologic Memory)

Answer 34

- High levels of IgG - Fast response time: takes 1-2 days - Quickly overcomes the infection - Memory cells are replenished

Question 35

The T Cell Response: Cell- Mediated Immunity

Answer 35

- Cytotoxic T cells (Tc) - Responsible for destroying abnormal cells Ex. Cells infected by viruses r bacteria, cancer cells, foreign cells Recognize antigens presented along with MHC class I

Question 36

T Cell Activation

Answer 36

a) A dendritic cell engulfs foreign antigen, presents antigen to a specific Tc - Tc is activated to undergo clonal expansion - Produces: Memory T cells and Cytotoxic T lymphocytes (CTLs) b) Once the CTLs are activated - any body cell can serve as APC c) Endogenous antigen is presented on the cell surface along with MHC class I - CTL attaches to abnormal cell and releases: 1) Perforins - enzymes that poke holes in the abnormal cell's membrane 2) Granzymes - enzymes that induce apoptosis (programmed cell death)