3: Antigens Flashcards
what is an antigen
any substance that can induce specific immune responses
another word for antigens
immunogens
what do b cell receptors (antibodies) recognize (5)
- peptides
- sugars
- lipids
- nucleic acids
- hormones
what do Th and Tc receptors recognize
peptides that have been processed or degraded
what do gamma/delta T cells recognize
lipids directly on pathogen surface
what is an allergen
antigen that induces an allergic reaction
what is an epitope
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)
another word for epitope
antigenic determinant
what is multivalency
some epitopes are repeated several times on a macromolecule
what are antigens
molecules recognized by the immune system
how do b cells recognize antigens
b cells have receptors (antibodies) that can bind directly to the native antigen
how do t cells recognize antigens
require presentation of the epitope by an MHC molecule
what about epitopes on a single antigen affects how antibodies can bind to the macromolecule
spatial arrangement of epitopes
what are antigenic determinants limited to (in epitopes)
limited to those portions of the antigen that bind to MHC molecules
2 types of epitopes
- linear
- discontinuous
what are haptens
small molecules that are not normally immunogenic but become antigens when linked to another structure (carrier)
what does a hapten linkage form
a new epitope which is now big enough to be bound by antibody or t cell receptors
haptens and drug allergies
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)
3 types of antibodies generated by haptens
- against the carrier
- against the hapten
- against the new epitope generated by the hapten-carrier linkage
what are t independent antigens
some antigens are immunogenic enough that t cells are not required to activate b cells for antibody production
2 characteristics of t independent antigens
- have repeating epitopes
- cross-link b cell receptors (antibodies) on the surface of a b cell
when are t independent antigens useful and why
occur very early in an immune response and assist in host clearance of certain pathogens
4 factors influencing antigenicity
- size
- complexity
- foreigness
- stability
how does the degree of difference of something affect the immune response
more different = stronger response
how does the length of time something is in the system affect the immune response
in system longer = more response
what influences immunogenicity (3+)
- host factors (genetics)
- age
- environmental factors (dose, exposure route, adjuvants)
what do adjuvents do
help immune system see antigen (keeps it around longer)
what is cross-reactivity
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)
what does cross-reactivity result in
specific immunity against apparently unrelated antigens
what happens to antigens encountered in tissues
taken up by dendritic cells (and macrophages) then moved to draining lymph nodes –> elicit IgG antibodies
what happens to antigens encountered on mucosal surfaces
taken up through specialized M cells or via dendritic cells that extend through the epithelial lining –> elicit IgA and IgE antibodies
what happens to antigens in processing
processed into smaller fragments (epitopes) that are presented to t cells to initiate a specific immune response
endogenous v exogenous antigen presentation
- exogenous: presented by MHC class II molecules
- endogenous: presented by MHC class I molecules
what are antigen-presenting cells
highly specialized that can display processed antigen as peptide fragments on the cell surface
what are autoantigens
antibodies and reactive t cells generated against self antigens
3 ways pathogens induce autoimmunity
- disruption of cell or tissue barrier
- molecular mimicry
- superantigen
what are tumor antigens
presented on the surface of tumor cells by MHC class I and II (not found on normal cells)
what are superantigens
- 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
what do antibodies and b and t cell receptors recognize
discrete determinants (epitopes) and demonstrate a high level of specificity
what do components of the innate immune system recognize
broad molecular patterns found in pathogens but not the host –> lack a high degree of specificity
