Adaptive Immunity

Question 1

Acquired

Answer 1

• Begins as soon as a pathogen is encountered for the very first time
• Adaptive response will not occur until a pathogen is encountered

Question 2

Very Specific

Answer 2

• Very targeted to a specific feature of a given bacterium, virus, toxin
• Immunity to one pathogen will not confer immunity to another

Question 3

Has a memory component

Answer 3

Produces a more effective response when a pathogen is encountered for the
second time-faster and stronger

Question 4

Consists of two components

Answer 4

1. Humoral (antibody mediated) immunity
2. Cell mediated immunity

Question 5

Antibodies

Answer 5

Proteins produced by the immune system that bind and inactivate foreign
antigen

Question 6

Immunogens

Answer 6

• Any foreign material that has the ability to active the adaptive immune system
  
  • Normally protein, polysaccharide, lipid material

Question 7

Epitopes

Answer 7

• The actual portion of the antigen that binds to the antibody
• A single antigen will have more than one epitope
  
  • Increases the ability of an antigen to activation the immune system ->
    immunogenicity
  • Each epitope requires a distinct antibody

Question 8

Hapten

Answer 8

• Low molecular weight compound that is too small on its own to activate
  adaptive immunity
• Not immunogenic
• Can bind to other molecules such as protein in blood and tissues
  
  • Becomes strongly immunogenic
    
    • An allergy forms
      
      • Ex) penicillin

Question 9

Antibody Mediated Immunity

Answer 9

• Antibodies (Ab) are glycosylated protein molecules
  
  • Also called immunoglobulins (Ig)
  • Consist of 4 subunits
    
    • Two identical heavy chains
    • Two identical light chains
    • Chains are assembled creating three distinct regions
      
      • 2 identical variable regions (Fab regions)
        
        • Provide the specificity of the antibody
      • 1 constant region (Fc region)
        
        • Allows for interaction with immune cells
        • Based on differences in the Fc region there are five different types of antibody

Question 10

Classes of Antibody

Answer 10

1. Immunoglobulin M (IgM)
2. Immunoglobulin G (IgG)
3. Immunoglobulin A (IgA)
4. Immunoglobulin D (IgD)
5. Immunoglobulin E (IgE)

Question 11

Immunoglobulin M (IgM):

Answer 11

• Pentameric
  
  • Five different antibody units form IgM
• Always the first antibody to be produced in
  response to an antigen
  
  • Primary antibody response
• Found on the surface of B lymphocytes
  
  • Remains in the blood
    
    • Unable to enter the tissues
• Low affinity for antigen
• Very good at agglutination

Question 12

Immunoglobulin G (IgG)

Answer 12

• Monomer
• Most predominate antibody in the blood
• Also present in the tissues

Question 13

Immunoglobulin A (IgA)

Answer 13

• Dimeric
• Secreted at mucosal sites
  
  • Saliva, tears, mucous
• Important defense against respiratory, reproductive, digestive tract infections

Question 14

Immunoglobulin D (IgD)

Answer 14

• Monomer
• Located on the surface of B cells
• Important in activation of B cells to begin producing antibody against a specific antigen

Question 15

Immunoglobulin E (IgE)

Answer 15

• Monomer
• Binds to receptors located on the surface of mast cells and basophils
  
  • Binding of IgE-antigen complex triggers degranulation and histamine release
    
    • Allergy

Question 16

Antibody Functions

Answer 16

1. Neutralization
2. Opsonization
3. Agglutination
4. Antibody Mediated cytotoxicity
5. Complement activation

Question 17

Neutralization

Answer 17

• Antibodies bind to antigen blocking attachment sites
  
  • Prevents bacteria, virus and toxin entry into tissues and host cells

Question 18

Opsonization

Answer 18

• Antibodies coat the surface of the bacterial cell
  
  • Attracts phagocytes
  • Greatly enhances the rate of phagocytosis
  • Phagocyte has the ability to interact with the Fc region of the antibody

Question 19

Agglutination

Answer 19

• Each class of antibody can bind to a minimum of 2
  identical antigen units
• Clumps together many antigens
• Allows phagocytosis to occur more efficiently

Question 20

Antibody Mediated cytotoxicity

Answer 20

• Attachment of antibody to parasites recruits eosinophils
  
  • Eosinophils attach to the Fc component of antibodies
  • Activated eosinophil releases reactive oxygen species and hydrolytic enzymes
  • Parasite is destroyed

Question 21

Complement activation

Answer 21

• Complement is a system consisting of a series of proteins found in the blood
  
  • Can be activated by antibody that is bound to a bacterial cell
    
    • Classical pathway of complement activation
• Create a number of different immune responses when activated
  
  • Memebrane Attack Complex (MAC) attack complex forms
    
    • Inserts into the membrane of bacterial cell forming a pore
    • Contents of the cell leak and the bacterium dies

Question 22

Activation of Antibody Mediated Immunity

Answer 22

• B cells are antigen presenting cells
  
  • Macrophages and dendritic cells also perform antigen presentation
  • All antigen presenting cells can insert MHC II into the plasma membrane
• Antibodies are produced against exogenous antigen
  
  • Antigen that exists outside of the cell in the surrounding extra-cellular fluid
    
    • Can be bacteria, virus, parasite, toxin, etc.
  • Once antibodies are secreted from B cells they can bind to and neutralize/opsonize these exogenous antigens

Question 23

What are the Steps in Antibody Production?

Answer 23

1. B cell phagocytoses exogenous antigen
2. T helper cells bind to MHC II-ANtigen complex resulting in T helper cell activation
3. Some of these newly produced B cells will become plasma cells

Question 24

B cell phagocytoses exogenous antigen

Answer 24

• Digested content in the phagolysosome will not be exocytosed to the extracellular fluid
  
  • Instead it will be complexed together with MHC II and inserted into the plasma membrane

Question 25

T helper cells bind to MHC II-ANtigen complex resulting in T helper cell activation

Answer 25

The activated T helper cell releases cytokines that bind to receptors on the B cell resulting in B cell proliferation

Question 26

Some of these newly produced B cells will become plasma cells

Answer 26

- Actively transcribe, translate and secrete an identical antibody protein to the extra- cellular fluid - These antibodies are specific to the original exogenous antigen - A smaller fraction of newly produced B cells will become memory cells - These will be used in subsequent encounters with the same antigen - They will not produce antibodies during the current response

Question 27

Primary Antibody Response

Answer 27

- Occurs the very first time a specific antigen is encountered - Can be a natural encounter or an artificial encounter (ex: vaccination) - Produces a weak antibody mediated response - Slow production of low levels of antibody - Results in the production of memory B cells: major goal

Question 28

Secondary Antibody Response

Answer 28

- Occurs every additional time (after the primary response) a specific antigen is encountered - Produces a strong antibody mediated response - Rapid production of high levels of antibody - So rapid that the pathogen will not be able to establish infection - No disease occurs

Question 29

Tolerance

Answer 29

- Tolerance prevents immune responses against self-antigens - Any immune cells that are found to recognize self-antigens are destroyed early on in development - Helps to prevents auto-immune disease

Question 30

Cell Mediated Immunity

Answer 30

- Recognizes and destroys abnormal cells present in the body - Cells infected with virus or obligate intracellular bacteria - These are endogenous antigen because they are present inside of the host cell - Involves cytotoxic T cells - Diseased host cell will display endogenous antigen in the plasma membrane complexed together with MHC I - Cytotoxic T cells will bind to MHC I-Antigen complex using their T cell receptor (TCR) - This results in activation of the cytotoxic T cell triggering it to release perforins and granzymes that cause death of the infected host cell - In order to clear a viral infection both antibody mediated immunity and cell mediated immunity are required