3. Adaptive Immunity

Question 1

What are 5 needs for an adaptive immune system?

Answer 1

1. Pathogens have devised multiple clever mechanisms to evade the innate immune response
2. Zoonoses are a real threat to those organisms that share immune defense mechanisms (innate)
3. The body needed to devise defense mechanisms that could ADAPT to each of these organisms no matter how diverse they were
4. Expansion of ecological niches undoubtedly result in exposure to new and broader range of pathogens
5. Highly advantageous to remember pathogens

Question 2

Acquired (adaptive) mechanisms of immunity

Answer 2

• Necessary if pathogenic organisms breach innate defenses and spread through host
• Exquisite specificity - can respond to one thing and not something related
• Adaptable to new situations
• Systemic
• Includes mechanisms such as: antibodies, antigen presentation, recognition of self/non-self
• Forms the basis of memory

Question 3

What are the 2 main regions of the antibody?

Answer 3

1. Recognition function: specifically binds to individual antigens
   - variable, complementary in shape
2. Biological function: communicate with complement and phagocytes
   - constant
   - FC portion

Question 4

Antigen vs. Antibody

Answer 4

Antigen: a macromolecule that induces specific antibody formation

Antibody: a protein or glycoprotein that binds antigen

Question 5

Molecular structure of antibodies

Answer 5

The basic antibody unit is composed of 2 identical heavy chains and 2 identical light chains
- generates 2 discrete sites for binding antigen
- held together by disulfide bonds (S-S)

Question 6

What provides a mechanism for increased affinity in antibodies?

Answer 6

Certain segments of the variable region are hypervariable = overtime antibodies get better and better

Question 7

What is the role of the hinge region of antibodies?

Answer 7

Increases the efficiency of binding
- need the flexibility in the arms to effectively bind
- want a small AA (Gly) in the hinge region

Question 8

What is the Fc region of the antibody a major determinant of?

Answer 8

Antibody functional properties
- when thinking about antibody diversity across species, think of the Fc

Question 9

What are the 5 different antibody classes?

Answer 9

1. IgM
2. IgG
3. IgA
4. IgE
5. IgD

*Types of antibodies are defined based on their Fc regions; could be binding the same thing but different fxn based on the Fc

Question 10

How do antibodies provide links btw innate and adaptive immunity?

Answer 10

1. Conventional direct recognition
   - a phagocyte recognizes conserved surface components on a bacterium, leading to internalization and killing
2. Cooperation between innate and adaptive components
   - B lymphocytes produce antibodies that recognize a variable component on the surface of a bacterium by means of a highly variable region of the antibody. The constant (non-variable) region is then recognized by FcRs on phagocyte linking innate and adaptive responses

Question 11

What is the complement system made up of? What are the functional outcomes?

Answer 11

About 25 plasma proteins that react with one another to opsonize pathogens and induce a series of inflammatory response that help to fight infection

Functional outcomes: trigger inflammatory responses, attract phagocytes, promote phagocytosis by opsonization, directly attack the membrane of a microbe, and stimulation of antibody production

Question 12

What points to the importance of the complement system?

Answer 12

The establishment and maintenance of redundant mechanisms

Question 13

What antibodies can activate complement?

Answer 13

IgG and IgM
= different antibodies have the capacity to activate complement

Question 14

What cells produce antibodies? Antibodies are the secreted form of what?

Answer 14

B cells (aka B lymphocytes)

Antibodies are the secreted form of the B cell antigen receptor. The more general term for both membrane and secreted form of the molecule is immunoglobulin

Question 15

What does the production of antibodies by B cells constitute? What is it complementarty to?

Answer 15

Constitutes humoral immunity, which is complementary to the cell-mediated immunity provided by T cells
- Both are part of the adaptive response
- T cell-mediated responses are mediated by direct cell-cell interaction (local)
- B cell mediated responses through antibodies are systemic
- Antibodies carried rapidly through the blood or lymph or secreted through epithelial layers to protect the interface btw animal and environment

Question 16

What is Clonal selection theory?

Answer 16

Antibodies are formed BEFORE antigens are ever seen by the body and they are SELECTED by antigen
- Selection: antigen binds lymphocyte (B cell) bearing a complementary receptor
- Activation: activated B cell then forms an expanded clonal pool

Provides a cellular basis for the generation of effector and memory cells

Question 17

Primary vs. Secondary responses

Answer 17

Primary response
- occurs when a B cell is first activated by an antigen
- B cell proliferates and differentiates to form plasma cells and memory B cells
- plasma cells produce antibodies
- memory cells are differentiated B cells capable of rapid conversion to plasma cell upon subsequent stimulation with same antigen

Secondary response
- another exposure to the same antigen
- memory B cells rapidly form plasma cells and additional memory cells
- faster and produces MORE antibodies than the primary response

Question 18

How does affinity maturation provide specificity upon reimmunization?

Answer 18

• After B cell activation some cells migrate to germinal centers where rapid proliferation leads to changes in immunoglobulin genes encoding antibodies
• Some of these mutations affect the antigen-binding regions and result in higher affinity for antigen = AFFINITY MATURATION
• Some result in changes in the effector fxns of antibodies secreted from germinal center B cells = ISOTYPE SWITCH (changes in antibody class/isotype)

Question 19

What does initial exposure to an antigen result in the production of?

Answer 19

• The production of low affinity antibodies, but continued exposure to antigen leads to the production of high affinity antibodies. In the PRIMARY antibody response, B cells are activated to produce IgM antibody
• By 3-5 days, specific antibodies, mainly of the IgM isotype, appear in the serum and the concentration (titer) increases until a peak is reached in 10-14 days

Question 20

After some weeks following immunization what happens to antibody titers? What happens upon re-immunization?

Answer 20

• Antibody titers fall to pre-immunization levels after some weeks
• Upon re-immunization, there is a more rapid and extensive development of antibody-producing cells in regional lymph nodes, and many of them undergo an ISOTYPE SWITCH to produce IgG or other immunoglobulin classes of specific antibodies
• As a result, in most cases following re-immunization, serum antibodies are primarily IgG and have a greater affinity for antigens; also, antibody titers are higher and persist for longer periods

Question 21

How do the differences in the primary and secondary response to antigen exposure relate to allergy and anaphylactic reactions?

Answer 21

Differences
- Variations in immune response (eg. abundance and location of mast cells)
- Location and distribution of smooth muscle
- Rate of antigen degradation
- Responsiveness to inflammatory mediators

Question 22

A newly hatched chicken is unable to use its own immune system to fight invasion during the first few days to week of its life. How is it protected?

Answer 22

Maternal antibodies
- it is the antibodies not the cells that get transferred therefore, there is no capacity for cell proliferation; once antibodies are used they are gone