ICL 1.1: Introduction to Adaptive Immunity

Question 1

what is an antigen?

Answer 1

any molecule that stimulates the immune system

• proteins
• environmental like dust or pollen

Question 2

what is an epitope?

Answer 2

the specific region of an antigen that binds the immunoreceptor

an antigen can have multiple epitopes

Question 3

what is the cellular part of the adaptive immune system?

Answer 3

cell-mediated immunity by T cells

secreted and/or cell surface molecules

they provide signals for the maturation and/or
differentiation of other leukocytes

Question 4

what is the humoral part of the adaptive immune system?

Answer 4

antibody mediated by B cells

antibodies target cells and molecules for removal

Question 5

what are APCs?

Answer 5

antigen presenting cells

includes macrophage, dendritic, epithelial, and B cells

Question 6

where are lymphocytes usually found?

Answer 6

lymphoid tissues and organs

Question 7

what are primary/central lymphoid tissues?

Answer 7

sites of where lymphocytes develop and mature

T cells = thymus

B cells = BM

Question 8

what are secondary lymphoid tissues?

Answer 8

they’re distributed throughout the body and are sites where naive lymphocytes encounter antigen and become activated

ex. lymph nodes, spleen, adenoids, tonsils, Peyer’s patches in SI, appendix

Question 9

where do antigens go once they’re inside the body?

Answer 9

antigens are carried to the naïve lymphocytes in secondary lymphoid tissue, via the lymphatics

Question 10

where are lymph nodes located?

Answer 10

lymph nodes lie at the junctions of lymphatic vessels, which collect extracellular fluid (lymph) from the tissues

antigens found in the tissues eventually are carried to lymph nodes

Question 11

what are the functions of the spleen?

Answer 11

1. a site of lymphocyte activation for blood-borne antigens

2. storage of immune memory (memory lymphocytes)

Question 12

where are the B and T cells located in the spleen?

Answer 12

the white pulp!!!

B cells are in the germinal center

T cells are in the PALS

Question 13

what is GALT?

Answer 13

gut associated lymphoid tissues

ex. tonsils, adenoids, appendix, Peyer’s patches

Question 14

what is BALT?

Answer 14

bronchial associated lymphoid tissues

lymphoid tissue that lines the respiratory tract

Question 15

what type of antibody does the GI tract have alot of?

Answer 15

IgA

Question 16

what does TCR stand for?

Answer 16

T-cell receptor

Question 17

how does antibody binding work?

Answer 17

Ig/TCR are highly specific for a given antigen

antibodies made during infection with measles virus bind to the virus and prevent reinfection with measles virus

but antibodies made during infection with measles virus do not bind to influenza virus

Question 18

what are TCRs?

Answer 18

T cell receptor recognizes peptide associated with MHC molecule

MHC = major histocompatibility complex

Question 19

how is our immune response made specific?

Answer 19

the specificity of our immune responses resides in receptors like TCR and B cell receptors

Question 20

what does a B cell receptor do?

Answer 20

it’s a surface immunoglobulin that recognizes an antigen

Question 21

what’s the structure of a B cell receptor?

Answer 21

the immunoglobulin molecule is composed of two pairs of chains (H-heavy and L-light; mw), each of which can be divided into domains based on sequence similarity:

• V region (variable)
• C region (constant)

surface immunoglobulin has a light chain and a heavy chain

there’s also a transmembrane region and an antigen-binding site

Question 22

what’s the difference between the structure of an antibody and B cell receptor?

Answer 22

surface immunoglobulin has a transmembrane region that an antibody doesn’t have

Question 23

what’s the structure of a TCR?

Answer 23

TCR is made of an α and β chain

there’s an antigen binding site that is both on the α and β chain

there’s also a transmembrane region

Question 24

what are the different regions of the light and heavy chains of immunoglobulin?

Answer 24

both the light and heavy chain can be divided into domains = V region and C region

the V-region is variable and where there’s antigen binding

the C-region is constant and is what engages the innate immune system

Question 25

what defines an immunoglobulin’s antigen specificity?

Answer 25

hypervariable domains in each V region

you can look at the AA that make up both the heavy chain V region and the light chain V region

depending on which AAs are present in the binding pocket, it will tell you which antigen is most likely to bind

Question 26

where do antigens bind to immunoglobulin?

Answer 26

antigens bind in the pockets of the hyper variable regions of each arm of the immunoreceptor

in the V-region

Question 27

what are the steps in clonal selection?

Answer 27

during development, progenitor cells give rise to large numbers of lymphocytes, each with a different specificity

after an pathogen binds to a lymphocyte, there’s proliferation and differentiation of pathogen-activated lymphocytes to form a clone of the effector cell specific to that pathogen

effector cells eliminate pathogens!

clinical selection leads to the expansion of antigen-specific and pathogen-specific lymphocytes

Question 28

what is clonal selection?

Answer 28

each lymphocyte bears a single type of receptor of a unique specificity

interaction between a foreign molecule and a lymphocyte receptor leads to lymphocyte activation

activated lymphocytes will bear receptors of identical specificity to those of parental cell

lymphocytes bearing receptors for self molecules are deleted at an early stage in lymphoid cell development

Question 29

what do T cell antigen receptors recognize?

Answer 29

B cell produce Ab that can recognize native or denatured molecules

however, T cell antigen receptor CANNOT recognize intact protein antigens, but responds to peptide fragments bound to the surface of another cell (antigen presenting cell)

T cells respond to a peptide bound to a MHC molecule displayed on the surface of another cell, called an antigen presenting cell (APC)

Question 30

what does MHC stand for?

Answer 30

major histocompatibility complex

Question 31

what are class I MHC molecules?

Answer 31

class I MHC molecules are expressed on the surface of ALL nucleated cells

they’re recognized by TCR of cytotoxic T cells (CD8)

**CD8 binds to class I MHC-peptide complex

source of peptide is in the cytoplasm

Question 32

what are class II MHC molecules?

Answer 32

class II MHC molecules are expressed on the surface of some nucleated cells, mainly APCs

they’re recognized by TCR of helper T cells (CD4)

**CD4 binds to class II MHC-peptide complex

source of peptide is in the phagosomes

Question 33

what’s the function of MHC molecules?

Answer 33

they’re used to activate T cells

MHC I binds peptides from proteins found in the cytoplasm

MHC II binds peptides from proteins found in the phagosomes

Question 34

how do class I MHC molecules work?

Answer 34

MHC I binds peptides from proteins found in the cytoplasm

1. virus infects cell
2. viral proteins synthesized in cytoplasm
3. peptide fragments of viral proteins are bound by MHC class I in ER
4. bound peptides are transported by MHC class I to the cell surface of CD8 cells
5. cytotoxic T cells recognize the complex of viral peptide with MHC class i and kills the infected cell

Question 35

how do class II MHC molecules work in a macrophage?

Answer 35

MHC II binds peptides from proteins found in the phagosomes

1. macrophage engulfs and degrades bacterium, producing peptides
2. bacterial peptides bound by MHC class II inside vesicles of macrophage
3. bacterial peptides transported by MHC class II to the cell surface of macrophages
4. TH1 cell recognizes the complex of peptide antigen with MHC class II and activates macrophage

Question 36

how do class II MHC molecules work in a B cell?

Answer 36

MHC II binds peptides from proteins found in the phagosomes

1. cell-surface immunoglobulin of B cell binds and engulfs and degrades bacterium, producing peptides
2. bacterial peptides bound by MHC class II inside vesicles of macrophage
3. bacterial peptides transported by MHC class II to the cell surface of macrophages
4. TH2 cell recognizes the complex of peptide antigen with MHC class II and activates B cell

Question 37

what’s the purpose of vaccines?

Answer 37

vaccination with pathogen-specific antigens or pathogens allows us to mimic the infection and induce protective immunity without inciting the primary disease

Question 38

how do allergies work?

Answer 38

allergies are unwanted inflammatory response that are mediated by the adaptive immune response

inhalation of pollen particles produces the symptoms of a respiratory infection through IgE-mediated degranulation of mast cells

mast cells release cytokines, histamine and other active substances

Question 39

what happens after a pathogen is recognized by the innate immune system?

Answer 39

after recognition of pathogen by innate system, APC’s present antigen to adaptive system to mount a clonal response

1. microbes enter through and break in skin and are phagocytksed by dendritic cells
2. dendritic cell matures and carries microbial antigens to local lymph node to become an antigen-presenting cell
3. APCs activates T cells to respond to microbial antigens
4. activated T cells migrate to site of infection to help eliminate residual microbes