Principles of Adaptive Immunity

Question 1

Innate Immunity

Answer 1

Focus defense mechanisms onto the site of infection

• Non specific
• Non adaptive (no memory)

Question 2

Adaptive Immunity

Answer 2

Focus defense mechanisms onto the pathogen itself

Question 3

Specificity

Answer 3

Lymphocytes express antigen receptors that recognize specific features (antigens) of a microorganism = adaptive immune system can distinguish between different microorganisms

Question 4

Immune Memory

Answer 4

Second encounter with the same pathogen will induce a more rapid and efficient adaptive immune response

Question 5

Naive Lymphocytes

Answer 5

Have been exported from primary lymphoid tissues into blood and secondary lymphoid tissues

• have not been activated in response to an infection
• function: survey the body for infection

Question 6

Effector lymphocytes

Answer 6

Activated lymphocytes that undergo proliferation and are specialized to perform a particular function
- effector function: how they eliminate pathogens from the body

Question 7

Pathogen

Answer 7

Microbe that allows it to interfere with bodily functions and cause disease

Question 8

Series of events that occur after pathogens adhere to epithelium

Answer 8

Skin wound allows pathogens to penetrate epithelium –> proinflammatory cyto/chemokines are released –> local infection, innate immunity –> DC take infection to lymph node and stimulate adaptive immunity –> effector cells and molecules of adaptive immunity travel to the infected tissue

Question 9

B-lymphocytes (B cells)

Answer 9

B cell receptor is also referred to as an immunoglobulin (Ig)
- Soluble forms of BCRs referred to as antibodies

Question 10

T-lymphocytes (T cells)

Answer 10

Surface expressed T cell receptor

- TCR is NEVER secreted

Question 11

Structure of BCR and TCR

Answer 11

Variable region: antigen binding

Constant region: anchor the receptor to the cell membrane (associated with signal transduction proteins)

Question 12

When the BCR is secreted as an _______, the constant region determines the effector function of the antibody

Answer 12

Antibody

Question 13

What cell type is the bridge between adaptive and innate immunity?

Answer 13

Dendritic cells

Question 14

Where do B cells and T cells develop?

Answer 14

Bone marrow; Thymus

Question 15

What components of pathogens do antigen receptors recognize?

Answer 15

• Protein, carbs, and lipids

- Risk of developing cells that recognize self-protein/carbs/lipids

Question 16

Macrophages and neutrophils have ____ with broad specificity to recognize multiple microbes and distinguish between self and non self

Answer 16

TLR (toll like receptor)

Question 17

_____ and _____ come together to form antigen-binding site

Answer 17

Heavy and light chains

Question 18

Do B and T cells recognize the same form of the same antigen?

Answer 18

NO, recognize different forms of the same antigen due to their effector functions

Question 19

BCR recognizes ____ of an antigen

Answer 19

The native form

Question 20

What part of the antigen do TCR recognize?

Answer 20

Peptides derived from the proteolytic degradation of the antigen

Question 21

Pathway of TCR recognition

Answer 21

Native protein antigen –> denatured protein –> peptide antigens derived from denatured protein –> TCR bind to peptide:MHC molecule complexes

Question 22

T cell effector function

Answer 22

To detect infected cells and provide activation signals to other leukocytes (controlling adaptive immune response)

Question 23

How do dentritic cells activate adaptive immunity?

Answer 23

DC are present in tissues, along with macrophages

• when innate becomes overwhelmed, DC engulf pathogen and migrate to lymph nodes via afferent lymph vessels
• OR, pathogens can be carried to lymph nodes and then entangled by DC
• OR, pathogens in blood can be engulfed by DC in the spleen

Question 24

Role of APC in activating adaptive response

Answer 24

Naive T cells entering lymph node can survey the antigens displayed by DCs
- antigen specific T cells will be activated to proliferate and differentiate into effector T cells

Question 25

Effector T cells migrate to ____

Answer 25

Site of infection from the lymph nodes

Question 26

Effector function

Answer 26

- activate macrophages to kill pathogens taken up by phagocytosis (helper T cells) - kill infected cells (cytotoxic T cells)

Question 27

What happens to the other portion of helper T cells (effector T cells)?

Answer 27

Remain in lymph node and provide activation signals to antigen specific B cells

Question 28

Function of bone marrow and thymus

Answer 28

Maintain a steady state production of B and T cells with varying receptors

Question 29

Dendritic cells

Answer 29

- Antigen processing: potent in activating T cells, degrade phagocytized pathogen and display a piece on the surface by MHC - Antigen presentation

Question 30

Dendritic cells provide the ____ and the ____ _____ for adaptive response

Answer 30

Antigen; activation signal

Question 31

Major Histocompatibiliy Complex (MHC)

Answer 31

Complex of immune system genes that encode membrane proteins, which are involved in presenting peptides to T cells

Question 32

Do MHC proteins have broad or specific specificity?

Answer 32

Broad, can bind peptides derived from many different pathogens

Question 33

MHC class 1

Answer 33

Expressed on surface of most nucleated cells in the body | - recognized by cytotoxic T cells that express co receptor CD8

Question 34

MHC class 2

Answer 34

Expressed on surface of 3 leukocyte lineages: - DC, macrophages, B cells - recognized by helper T cells that express co receptor CD4

Question 35

Function of MHC class 1

Answer 35

Reports the "health status" of the cell - proteins in the cell are degraded into short peptides after performing their function --> peptides are pumped into the ER and bound by newly synthesized MHC 1 proteins --> transported to cell surface

Question 36

Viral proteins and MHC 1

Answer 36

Viral proteins can also be degraded in the cytoplasm and transported to ER --> bind to MHC 1 --> MHC 1-viral peptide complexes will accumulate on surface of the cell for recognition by virus-specific CTL (cytotoxic T cells)

Question 37

Activation of CTLs

Answer 37

Activated in secondary lymphoid tissues by DC - proliferate/differentiate to effector CTL --> enter circulation and are recruited to site of viral infection - effector function: recognize/eliminate infected host cells

Question 38

Function of MHC class 2

Answer 38

Extracellular pathogens! - macrophage engulfs/degrades bacterium into peptides --> peptides bound by MHC 2 and transported to cell surface --> helper T cell recognizes complex and activates macrophage - effector helper T cells are recruited to site of infection and will activate effector function of other leukocytes responding to infection (macrophages and B cells)

Question 39

Effector helper T cell activation of macrophages

Answer 39

``` Some pathogens (listeria) can resist being killed in macrophage lysosomes and persist in cytoplasm - effector helper T cells activate macrophage production of powerful reactive oxygen species to kill intracellular bacteria ```

Question 40

B cell response to infection in secondary lymphoid tissues

Answer 40

Antigen binds to B cell receptor --> facilitates internalization of the antigen for processing and presentation by MHC 2 proteins - activation by effector helper T cells will induce B cell proliferation/differentiation to plasma cells - plasma cells synthesize and secrete original antigen receptor as antibody

Question 41

Effector helper T cell activation of B cells

Answer 41

Cell-surface immunoglobulin of B cell binds to bacteria --> cell engulfs and degrades them = peptides --> bacterial peptides bound by MHC 2 in endocytic vesicles --> bound peptides transported by MHC 2 to the cell surface --> helper T cell recognizes complex of peptide antigen with MHC 2 and activates B cell

Question 42

Do B cell receptors and antibodies recognize native protein antigens?

Answer 42

Yes, DC can release unprocessed antigens that are recognized by B cells in addition to processed/presented antigens recognized by T cells

Question 43

____ signals are required for lymphocyte activation

Answer 43

2; important mechanism of peripheral tolerance (tolerance to self protein) Signal 1: recognition of antigen Signal 2: delivered by another cell in form of cytokines and surface proteins

Question 44

Antigen-activated T cells require a second signal provided by ____

Answer 44

Dendritic cells

Question 45

Antigen-activated B cells require a second signal provided by ______

Answer 45

Effector helper T cells

Question 46

DC and effector T cells must become ____ before they can activate mature T cells

Answer 46

Licensed (must have taken up a pathogen)

Question 47

Once B cells are activated by antigens, they have ______ to collaborate with helper T cells or they become unresponsive

Answer 47

24 hours