3: Antigens

Question 1

what is an antigen

Answer 1

any substance that can induce specific immune responses

Question 2

another word for antigens

Answer 2

immunogens

Question 3

what do b cell receptors (antibodies) recognize (5)

Answer 3

• peptides
• sugars
• lipids
• nucleic acids
• hormones

Question 4

what do Th and Tc receptors recognize

Answer 4

peptides that have been processed or degraded

Question 5

what do gamma/delta T cells recognize

Answer 5

lipids directly on pathogen surface

Question 6

what is an allergen

Answer 6

antigen that induces an allergic reaction

Question 7

what is an epitope

Answer 7

smaller portion of a larger molecule that has the structure bound by the antibody or t cell receptor (site within an antigen to which the antigen receptor binds)

Question 8

another word for epitope

Answer 8

antigenic determinant

Question 9

what is multivalency

Answer 9

some epitopes are repeated several times on a macromolecule

Question 10

what are antigens

Answer 10

molecules recognized by the immune system

Question 11

how do b cells recognize antigens

Answer 11

b cells have receptors (antibodies) that can bind directly to the native antigen

Question 12

how do t cells recognize antigens

Answer 12

require presentation of the epitope by an MHC molecule

Question 13

what about epitopes on a single antigen affects how antibodies can bind to the macromolecule

Answer 13

spatial arrangement of epitopes

Question 14

what are antigenic determinants limited to (in epitopes)

Answer 14

limited to those portions of the antigen that bind to MHC molecules

Question 15

2 types of epitopes

Answer 15

• linear

- discontinuous

Question 16

what are haptens

Answer 16

small molecules that are not normally immunogenic but become antigens when linked to another structure (carrier)

Question 17

what does a hapten linkage form

Answer 17

a new epitope which is now big enough to be bound by antibody or t cell receptors

Question 18

haptens and drug allergies

Answer 18

drug allergens are common due to the tendency for haptens to bind larger proteins (ex: penicillin binds to albumin, urushiol in poison ivy binds to skin proteins)

Question 19

3 types of antibodies generated by haptens

Answer 19

• against the carrier
• against the hapten
• against the new epitope generated by the hapten-carrier linkage

Question 20

what are t independent antigens

Answer 20

some antigens are immunogenic enough that t cells are not required to activate b cells for antibody production

Question 21

2 characteristics of t independent antigens

Answer 21

• have repeating epitopes

- cross-link b cell receptors (antibodies) on the surface of a b cell

Question 22

when are t independent antigens useful and why

Answer 22

occur very early in an immune response and assist in host clearance of certain pathogens

Question 23

4 factors influencing antigenicity

Answer 23

• size
• complexity
• foreigness
• stability

Question 24

how does the degree of difference of something affect the immune response

Answer 24

more different = stronger response

Question 25

how does the length of time something is in the system affect the immune response

Answer 25

in system longer = more response

Question 26

what influences immunogenicity (3+)

Answer 26

• host factors (genetics)
• age
• environmental factors (dose, exposure route, adjuvants)

Question 27

what do adjuvents do

Answer 27

help immune system see antigen (keeps it around longer)

Question 28

what is cross-reactivity

Answer 28

process by which one epitope is similar enough to trigger a response against another epitope, even on very different molecules (2 unrelated antigens share an epitope)

Question 29

what does cross-reactivity result in

Answer 29

specific immunity against apparently unrelated antigens

Question 30

what happens to antigens encountered in tissues

Answer 30

taken up by dendritic cells (and macrophages) then moved to draining lymph nodes –> elicit IgG antibodies

Question 31

what happens to antigens encountered on mucosal surfaces

Answer 31

taken up through specialized M cells or via dendritic cells that extend through the epithelial lining –> elicit IgA and IgE antibodies

Question 32

what happens to antigens in processing

Answer 32

processed into smaller fragments (epitopes) that are presented to t cells to initiate a specific immune response

Question 33

endogenous v exogenous antigen presentation

Answer 33

• exogenous: presented by MHC class II molecules

- endogenous: presented by MHC class I molecules

Question 34

what are antigen-presenting cells

Answer 34

highly specialized that can display processed antigen as peptide fragments on the cell surface

Question 35

what are autoantigens

Answer 35

antibodies and reactive t cells generated against self antigens

Question 36

3 ways pathogens induce autoimmunity

Answer 36

• disruption of cell or tissue barrier
• molecular mimicry
• superantigen

Question 37

what are tumor antigens

Answer 37

presented on the surface of tumor cells by MHC class I and II (not found on normal cells)

Question 38

what are superantigens

Answer 38

• secreted exotoxins that are highly mitogenic and stimulatory for t cells
• do not require prior processing in order to bind to the t cell receptor
• cross-link MHC and TCR to overstimulate t cells and drive hyperinflammation

Question 39

what do antibodies and b and t cell receptors recognize

Answer 39

discrete determinants (epitopes) and demonstrate a high level of specificity

Question 40

what do components of the innate immune system recognize

Answer 40

broad molecular patterns found in pathogens but not the host –> lack a high degree of specificity