Chapter 3: Antigens and MHC

Question 1

What is an antigen

Answer 1

a foreign substance recognized by the immune system

Question 2

what is an immunogen

Answer 2

a substance capable of causing an adaptive immune response

Question 3

what is an epitope

Answer 3

a marker on an antigen that triggers an antibody response

Question 4

what is the major histocompatibility complex (MHC)

Answer 4

molecules that mark cells as “self”

Question 5

what is an antibody

Answer 5

molecules produced in response to an antigen

ex. immunoglobulins

Question 6

what does it mean to opsonize

Answer 6

to coat an antigen with antibodies or complement proteins for enhanced immune response

Question 7

what do complement proteins do

Answer 7

they help antibodies by:
* destroying bacteria
* inducing inflammatory responses
* regulating immune reactions

Question 8

how does age affect the immune system

Answer 8

older individuals have a decreased response, while neonates have an underdeveloped immune system

Question 9

what antigen characteristics determine immunogenicity

Answer 9

• molecular size
• foreignness
• chemical complexity
• ability to be processed and presented within MHC complex

Question 10

how does antigen size affect immunogenicity

Answer 10

larger antigens have stronger immunogenicity

Question 11

what are exceptions to the immunogenicity size rule

Answer 11

some small compounds can be immunogenic

Question 12

what is foreignness in antigens

Answer 12

• how different an antigen is from the host
• the more unrelated an antigen is to the host, the more successful it is as an immunogen

Question 13

What are the three types of antigens based on foreignness

Answer 13

• autoantigens (self)
  *alloantigens (same species)
• heteroantigens (different species)
  *heterophile (unexpected cross reactions between species)

Question 14

How does chemical complexity affect antigenicity

Answer 14

• proteins and polysaccharides are strong immunogens
• nucleic acids, lipids, synthetic polymers, and oligosaccharides are weak immunogens

Question 15

How do carbohydrates function as immunogens

Answer 15

• less immunogenic than proteins
• cause T cell-independent responses

Question 16

Why are lipids and nucleic acids poor immunogens

Answer 16

they are not immunogenic unless linked to an immunogenic carrier

Question 17

can large molecules have multiple epitopes

Answer 17

Yes, each is capable of producing an immune response

Question 18

What are the two types of epitopes

Answer 18

• linear Epitopes
• conformational epitopes

Question 19

what is the difference between linear and conformational epitopes

Answer 19

• linear epitopes consist of sequential amino acids
  ex. single polypeptide chain
• conformational epitopes are one or more polypeptide chains

Question 20

What cells recognize epitopes

Answer 20

B and T cells

Question 21

What cell detects epitopes on the surface of a molecule

Answer 21

B cells

Question 22

what epitopes do T cells detect

Answer 22

• linear epitopes that have been degraded
• Requires antigen to be presented by MHC

Question 23

What is an antigenic determinant

Answer 23

another name for epitope

Question 24

What is cross-reactivity

Answer 24

when an immune response to one molecule also reacts with a different molecule due to similar/shared epitopes

Question 25

what is a hapten

Answer 25

a substance that is nonimmunogenic by itself but can form antigenic determinants when combined with a carrier * nonimmunogenic by itself but immunogenic with carrier

Question 26

what is a carrier molecule

Answer 26

a larger molecule that links with haptens to produce an immunogenic response

Question 27

what is an adjuvant

Answer 27

a substance delivered with an antigen to enhance the immune response *ex. adjuvants added to a vaccine

Question 28

what increases the immunogenicity of an antigen by stimulating an innate immune response

Answer 28

an adjuvant

Question 29

How do adjuvants affect the antigens location

Answer 29

they prevent the antigen from diffusing away from the injection site allowing immune cells to accumulate in the site. * This tricks the immune system into acting as if there was an infection

Question 30

what is an autoantigen

Answer 30

antigens that belong to the host and usually do not evoke an immune response

Question 31

When would autoantigens invoke an immune response

Answer 31

when an autoimmune condition arises

Question 32

what is an alloantigen

Answer 32

antigens that are from other members of the host's species * different blood types in humans

Question 33

what is a heteroantigen

Answer 33

antigens from other species *animal and human antigens are different

Question 34

what is a heterophile

Answer 34

Heteroantigens are antigens found in different species, but their structures are so similar that antibodies made to one can also react with the other. In other words, if your immune system makes antibodies against an antigen from one species, those antibodies might also attack a similar antigen from another species.

Question 35

What are the human MHC antigens called

Answer 35

human leukocyte antigens (HLAs)

Question 36

What complex plays a pivotal role in the development of humoral and cellular immunity

Answer 36

the major histocompatibility complex (MHC)

Question 37

where are the genes coding for MHC molecules located

Answer 37

they are found on the short arm of chromosome 6

Question 38

how are MHC genes divided

Answer 38

They are divided into 3 classes: *Class I *Class II *Class III

Question 39

what do class I of MHC genes include

Answer 39

Class one is found on 3 different loci *A *B *C (A Big Cat)

Question 40

what do class II of MHC genes include

Answer 40

Class II is found in the D region * DP * DQ * DR (Doesn't Question Danger)

Question 41

What do class III MHC genes include

Answer 41

Found in the middle of class I and II * C4a * C4b * C2 * B *cytokines (Clever Cats Battle)

Question 42

what is unique about the MHC

Answer 42

It is the most polymorphic gene system in humans

Question 43

what is an allele

Answer 43

alternative forms of a gene that code for a slightly different variation of the same product

Question 44

Where is MHC class one expressed

Answer 44

expressed on all nucleated cells

Question 45

How does the MHC class I vary in expression

Answer 45

* More expressed on lymphocytes and myeloid cells * less expressed on liver hepatocytes, neural cells, muscle cells, and sperm

Question 46

What regions on chromosome 6 codes for MHC class I molecules

Answer 46

MHC class I is encoded by regions A, B, and C (A Big Cat)

Question 47

What is the function of MHC class I

Answer 47

antigen presentation of endogenous antigens *Endogenous antigens: arise from the same cell

Question 48

What is the structure of MHC class I

Answer 48

* Has a glycoprotein dimer * alpha chain with 3 domains * one beta-2 microglobulin

Question 49

Why is MHC class I referred to as the endogenous pathway

Answer 49

Both peptides and MHC molecules arise within the same cell

Question 50

How does MHC class I interact with antigens

Answer 50

MHC Class I molecules interact with endogenous antigens and present them to CD8+ cytotoxic T cells (Tc)

Question 51

What happens when CD8+ Tc cells bind to the MHC Class I-antigen complex

Answer 51

CD8+ Tc cells release enzymes that destroy the target cell

Question 52

Where is MHC class II found

Answer 52

found on antigen presenting cells (APCs) include: * B lymphocytes * monocytes * macrophages * dendritic cells * thymic epithelial cells

Question 53

What type of antigens does MHC Class II recognize

Answer 53

exogenous antigens

Question 54

what is the function of MHC class II molecules

Answer 54

Presents exogenous antigens to CD4+ helper T cells

Question 55

What happens after MHC Class II presents an antigen

Answer 55

CD4+ T helper cells stimulate B cells to divide and differentiate into antibody-producing plasma cells

Question 56

Which MHC regions encode Class II molecules

Answer 56

* DP * DQ * DR (Don't Question Danger)

Question 57

What is the structure of MHC Class II

Answer 57

* Made of two noncovalently bound polypeptides * α chain with two domains * β chain with two domains

Question 58

why is MHC class II referred as the exogenous pathway

Answer 58

it processes and presents antigens that come from outside the cell