Chapter 3 - Antigens, Epitopes, and Immunogenicity Flashcards
State and Site: Immunization protocols
- what are the two ways that an antigen can elicit responses after inoculation?
- why might multiple inoculations be necessary?
- Particulate antigens elicit responses after inoculation by intracutaneous or intravenous routes at a broad range of doses
- Soluble antigens may require repeated immunizations
Adjuvant
- What is it?
- What does it do and how does it do it?
- what immune response does it generate?
- Increase response to an immunogen
- Stimulate localized inflammatory reaction at site of injection
- Slow release of the antigen
- Recruits phagocytic and inflammatory cells
- Better uptake of the antigen
Adjuvant
- what are two types?
- give examples of those types
- Types:
- Aluminum salts
- Mineral oil and they often contain bacteria or bacterial products
- Examples:
- Alum
- Freund’s Adjuvant (a mineral oil and water mixture either free or containing bacterial products)
- lipopolysaccharide (LPS)
- Muramyldipeptide
- What is a linear epitope?
- What is it related/not related to?
- Related to amino acid sequence of an antigen
- Not related to three-dimensional structure
What part of an antigen dictates the conformational epitope structure?
- Depends on antigen’s three-dimensional structure
Describe the region on the B cells that recognizes and binds epitopes:
- # of amino acids?
- # of sugars?
- 6–15 amino acids
- 2–7 sugars
- What size peptides can MHC I molecules bind to?
- What size peptides can MHC II molecules bind to?
- Class I MHC molecules can bind peptides of 8–10 amino acids
- Class II can accommodate peptides of 13–18 amino acids
Cross-Reactivity
- characteristics (2)?
- what happens?
- Nature is repeating patterns
- Epitopes may be shared by different antigens
- Reaction of an antibody with an antigen other than the one that induced its formation
Cross-Reactivity
- why does it occur (2)?
- what are some common tests where this might happen?
- Occurs because
- The exact same epitope is on the molecule
- Or a very similar to the epitope
- Use caution to not misdiagnose patient
- FSH, HCG, LH
Cross-Reactivity
- when is it a good thing?
- Can be helpful for vaccines
Tetanus toxin and tetanus toxoid
Major Histocompatibility Complex (MHC)
- What differentiates Class I & II from Class III?
- Only Class I, Class II MHC genes play a direct role in immune responses
- Class III encodes for cytokines and complement and other soluble proteins
Major Histocompatibility Complex (MHC)
- what are its limitations (2)?
- Limited by inherited haplotypes
- Individuals may respond differently to a particular antigen
Major Histocompatibility Complex (MHC)
- what are HLA?
- what do they do?
- Human MHC antigens involved in immune response called Human Leukocyte antigens
- Encode for proteins on the antigen presenting cell which present the antigen to a T-cell
Major Histocompatibility Complex (MHC)
- define polymorphic
- how are the alleles inhereted (number-wise)
- how are they expressed (dominant, co-dominant, recessive…)
- how many different sets can be inherited?
- MHC haplotypes are highly polymorphic:
- Genes have many alternate forms
- These alleles are inherited as sets
- One set of alleles from each parent
- – Co-dominantly expressed: the products of both sets of genes are expressed on cell surfaces
- Four different sets that can be inherited
Major Histocompatibility Complex (MHC)
- What happens when there is a hole in the repertoire?
- Hole in repertoire, an individual fails to respond to a certain antigen
Major Histocompatibility Complex (MHC): Class I
- what type of molecules to they present?
- what type of cells is this class found on?
- what region of the MHC encodes these?
- to what type of cell is the antigen presented and what happens to the antigen?
- endogenous antigens (from inside the cell as in an infected cell)
- Those in an infected cell
- Found on all nucleated cells
- Encoded by A, B, and C regions of the MHC
- Present antigen to cytotoxic T cells
- To kill infected cell
Major Histocompatibility Complex (MHC): Class II
- what type of molecules to they present?
- what type of cells is this class found on?
- what region of the MHC encodes these?
- to what type of cell is the antigen presented?
- Recognize exogenous antigens (from the environment)
- Found on antigen-presenting cells
- Encoded by the DR, DP, and DQ regions
- Present antigen to helper T cells
T-Cell Receptors
- what do they do?
- what do they need to do it?
- what are those regions composed of?
- T cells can recognize a variety of different antigens
- Achieved via T-cell receptors (TCRs)
- Composed of two heterodimers (either alpha,beta or gamma,delta) covalently linked by a single disulfide bond
T-Cell Receptors
- CD marker?
- what does that marker do?
- Associated with CD3
- - Which signals and activates the cell after antigen binding
Antigen Presentation
- what CD markers tend to be on these T cells?
- what do these T cells do once activated (4)?
- Activate CD4+ (class II) and CD8+ (class I) T cells
- Accessory or antigen-presenting cell binds a particular antigen
- Internalizes antigen
- Processes antigen biochemically
- Presents antigen to T cell in Class I or Class II molecule
Antigen Presentation
- where does Class I get the antigen added to the MHC?
- where does Class II get the antigen added to the MHC?
- Class I transported to Golgi compartment after synthesis
- Class II goes to endosomal compartment after invariant chain removal
Antigen Presentation
- what happens to Class I and II once they segregate in the cell after synthesis?
- Class I and class II segregate
- Class I interact with antigen peptides
- Class II are complexed to the invariant chain (Ii)
- What are some examples of natural haptens?
- What are some examples of artificial haptens?
- natural: penicillin, poison ivy
- artificial: vaccines
The Exquisite Specificity of the Immune System: Haptens
- what type of reactions are these used to study?
- what did Karl Landsteiner’s experiment discover?
- Used to study the specificity of antigen–antibody reactions
- Karl Landsteiner’s experiment produced an understanding that the diversity of an immune response can be immense
