(03) Antigens Flashcards
1
Q
(ANTIGENS)
What is an antigen?
More broadly, anything that can induce specific ______ (can be bound by __ or ___ receptors)
- what else are they called?
What five substances do B cell receptors (antibodies) recognize?
What do Th and Tc cell receptors recognize?
What is an allergen?
A
- any substance that induces antibody generation
- immune, B, T
- immunogens
- peptides, sugars, lipids, nucleic acids, hormones
- peptides that have been “processed” or degraded
- an antigen that induces an allergic reaction (but shouldn’t)
2
Q
(EPITOPES)
- _____ are smaller potions of large molecules that have the structure ____ by the ____ or _____ receptor. (also called an ______)
- A given macromolecule is recognized in ____. That is, each contains many ____ individually able to be bound by ___ or _____. (Some epitopes are repeated several times - this is called _____ - these can be the same or different _____)
- Antigens are the molecules recognized by the immune system - ____ are the sites within antigens to which the _____ binds.
A
- epitopes, bound, antibody, T cell, antigenic determinant
- parts, epitopes, antibody, T cell receptors, multivalency, epitopes
- epitopes, antigen receptor
3
Q
- Antigen specific cells (B cells and T cells) recognize ____ in different ways. B cells have ____ (called _____) that can bind directly to the native antigen. T cells require _____ of the epitope by an _____ (_______) molecule.
Different lymphocytes/receptors can recognize _____ epitopes on the same antigen
A
- epitopes, receptors, antibodies, presentation, MHC, major histocompatibility molecule
- different
4
Q
(EPITOPES)
- What may affect how antibodies can bind to the marcomolecule?
- antibody epitopes are limited to those ____ to the antibody, and ____ can exclude access of antibodies to ____ epitopes
- In theory, each 8-15 residues can constitute a _______, but the number of antigenic determinants per antigen is much _____ than would be theoretically be possible. The antigenic determinants are limited to those portions of the antigen that can bind to _____ molecules. What does this mean?
- What is the difference between a linear epitope and a discontuous epitope?
- Does which epitopes are recognized depend on the individual?
A
- the spatial arrangement of epitopes on a single antigen
- accesible, crowding, all
- separate antigenic determinant, less, MHC, This is why there can be differences in the responses of different individuals
- The AA of epitope are all in a line in linear, is discontinuous folding is involved (so formed by tertiary structure) and AA are discontinuous
5
Q
What are small molecules that are not normally immunogenic, but become antigens when linked to another structure (carrier)? How?
- ______ are common due to the tendency for them to bind larger proteins. Give two examples
A
- haptens, linkage forms a new epitope that is now big enough to be bound by antibody or T cell receptors
- drug allergies, penicillin binds to albumin, urushiol is toxic agent of poison ivy (converted to a reactive compound which reacts with skin proteins)
6
Q
(Blood Group Antigens)
Basically why can’t you mix blood?
A
- all humans make O antigen, depending on which blood type is present this molecule attaches in different ways and makes different epitopes - some of which may be seen as antigens by the host system
7
Q
(Hapten Immune Responses)
What three types of antigens will haptens generate?
A
- against the carrier, against the hapten, against the new epitope generated by the hapten-carrier linkage (right where the two bind (hapten and carrier))
8
Q
(T independent Ag)
- Some antigens are immunogenic enough that ____ are not required to activate _____ for antibody production
- These are usually very ____ molecules – have repeating ______ (multivalent or _____ Ag) – cross-link ______ (_____) on the surface of a _____
Stable _____
The responses can occur very ____ in an immune response and assist in _____ of certain pathogens
- When someone says you got a T independent Ag you know its ______, its got repeated ________, and doesn’t need ___ to get an antibody response
A
- T cells, B cells
- complex – epitopes, polymeric – B-cell receptors (antibodies), B cell
- in vivo
- early, host clearance
- big, multivalent epitope, T cells
9
Q
(Antigens)
What makes a good (something that produces a high response) antigen (four things)?
How good are each of these things?
- Proteins
- Simple polysaccharides
- complex carbohydrates
- nucleic acids
- lipids
A
- size (large - more epitopes), stability (needs to stick around - but can’t be so stable that it doesn’t break up cause you need to get t-cells involved), complexity, foreigness
- excellent if greater than 1000 Da
- poor - readily degraded in cells
- good, esp when bound to proteins
- poor unless bound to proteins
- poor unless bound to proteins
10
Q
(What influences Immunogenicity?)
(HOST FACTORS)
- genetics -
- There is a difference in the ability to _____ epitopes (which is done by _____)
- Age - _____ is paricular is deficient in _____ and _____ (_____) individuals
Also three environmental factors - what are they?
A
- present, MHC (where the variance is)
- specific immunity, neonates, senescent (old)
- Dose, Route of Exposure, Adjuvants
11
Q
STUDY THIS
A
if you can’t read this - look at ppt slide - page 7
12
Q
- What is the process by which one epitope is similar enough to trigger a response against another epitope, even on very different molecules?
What does this result in?
What are three examples?
- Binding pockets for an antibody are really specific for a specifc epitope - but can also bind epitopes that are pretty similar (look at picture Michael)
A
- cross-reactivity (basically two antigens share and epitope)
- specific immunity against apparently unrelated antigens
1. blood antigens - bacteria contain glycoproteins with carbohydrate side chains similar to those found on RBC
2. Mycobacterium species in soil can trigger antibodies that also bind Mycobacterium bovis
3. An ocular protein in horses is similar to one found in Leptospira
13
Q
(ANTIGEN EXPOSURE)
- route of ____ changes immune response
- Antigens encountered in tissues are taken up by _____ (and _____), then moved to _______. (tend to elecit _____ antibodies)
Ig = ______
G = ______
A
- exposure
- dendritic cells, macrophages, draining lymph nodes, IgG isotype
- immunoglobulin
- a type of immunoglobin
14
Q
(ANTIGEN EXPOSURE)
- Ag encountered on the mucosal surfaces are generally taken up through specialized ___ or via ____ that extend through the epithelial lining. (tend to elicit ___ and ____ isotype antibodies)
A
- M cells, dendritic cells, IgA, IgE
15
Q
(Antigen Processing)
- Antigens are usually processed into _____ (___) that are presented to ____ to initiate a specific _____.
- Exogenous (outside the cell) Ags are presented by _____ molecules
- Endogenous (inside the cell) Ags are presented by _____ molecules
- this determines what type of ____ gets involved
What is the degradation of proteins into peptides that can bind MHC molecules for presentation to T cells?
What is the display of antigens as peptide fragments bound to MHC molecules on the surface of a cell?
Which cells are highly specialized and can display processed antigen as peptide fragments on the cell surface?
A
- smaller fragments (epitopes), T cells, immune response
- MHC class II
- MHC class I
- T cell
- antigen processing
- antigen presentation
- antigen-presenting cells
