Lecture 27- Adaptive Immunity Flashcards
Adaptive Immunity
Specific immune response- specific to each pathogen
Several days to mobilize (innate immunity is faster)
Lymphocytes
Types of white blood cells, originate in marrow
2 types involved in adaptive immunity
B cells- mature in marrow
T cells- mature in thymus
Where do B cells mature?
Bone marrow
Where do T cells mature?
Thymus
Antigen (Ag)
Any foreign substance that elicits B or T cell response
Mostly proteins or polysaccharides on foreign organism
Epitope: Specific region exposed on surface of Ag
Specifically binds Ag receptor of B or T cell
Epitope
Specific region exposed on surface of Ag
Specifically binds Ag receptor of B or T cell
Self-Tolerance (Adaptive Immunity)
Depends on ability to distinguish self from non-self
Possible b/c individuals are biochemically unique
B and T cell Diversity
Many different B and T cell Ag receptors are generated via genetic recombination and deletion when cells are activated. SPECIFIC
Proliferation of B and T Cells
Once activated, multiple cell divisions-> many identical cells
Can become…
Effector cells
Memory cells
What are effector cells?
Short lived, work immediately against Ag, any pathogen producing Ag
- Plasma cells, helper T cells, cytotoxic T cells
What are memory cells?
Long lived, ready to divide if Ag reappears
Clonal Selection
Cell proliferation based on use
Immunological Memory
Long-term protection, result of prior infections
Primary Immune Response
Response to 1st exposure to Ag
Secondary Immune Response
Exposed to same Ag, respond faster- 2-7 days
Stronger, more prolonged
B cells and T cells are types of what?
Lymphocytes
B cells components
Membranes contain Y-shaped receptors
4 polypeptides
2 heavy chains
2 light chains
Constant (C) region
Variable (V) region
B cell Activation
No pathogen- inactive
Ag binds receptor
-> Cells secrete soluble form
= Antibody (Ab)
= Immunoglobulin (Ig)
T Cells Overview
Also have Ag receptors with 2 parts
Alpha and Beta chains
V and C regions
T cell Ag Receptors
Only bind Ag fragments on surface of host cell
Ag fragments displayed by
- Pathogen-detecting cells
- Infected cells
What are the 2 general responses in adaptive immunity?
Humoral Response and Cell-mediated Response
Humoral Response
Via antibodies in blood, lymph (B cells)
Cell-mediated Response
Infected host cells destroyed by specialized T cells (cytotoxic T cells)
Antigen Presenting Cell (APC)
Can be infected or specialized for detection
Presents antigen fragment
Helper T Cells
T cell with specific receptor bind APC Ag fragment
-> T cell activated via cytokines
Autocrine and paracrine signals
Positive feedback
Once active, helper T cells activate…
B cells- Humoral immunity
Cytotoxic T cells- Cell-mediated immunity
Cytotoxic T cells
Cell-mediated response
Use toxic proteins to kill infected cells before pathogens mature
Activated by…
- Signals from helper T cells
- Interactions with APC- bind Ag fragment
Activated Cytotoxic T cells release what?
Perforin: Forms pores
Granzymes: Initiate apoptosis
-> Infected cell dies, T cell moves on
B cells & Antibodies
Humoral response
B cell activated by helper T cell
Produces Memory B cells and plasma cells
Plasma cells secrete antibodies
Antibody Functions
DO NOT kill pathogen directly
3 mechanisms
- Neutralization
- Opsonization
- Complement System
Neutralization
One function of antibody- Binds virus, interferes with activity
Opsonization
One function of antibody- Binds bacteria, promotes phagocytosis
Complement System
One function of antibody- Antibody binds Ag on foreign cell
Complement protein binds Ab-Ag complex
Produces membrane attack complex- pores in PM
Water, ions rush in-> lysis
Vaccines
Harmless variant or derivative of a pathogen that stimulates adaptive immune response
How do vaccines work?
Stimulate primary immune response
Pathogen triggers secondary response-> No illness
Live attenuated vaccine
Live but weakened, avirulent form of pathogen (cannot cause sickness)
Inactivated vaccine
Whole pathogen, killed (by heat or chemicals)
Subunit vaccine
Only part of pathogen (antigen containing epitope)
DNA/mRNA
DNA/mRNA containing gene for antigen, expressed within vaccinated individual
Antigenic Drift
Small changes in viral antigens due to mutation
Antigenic Shift
Major changes in vial antigens due to reassortment/recombination
Strain Replacement
Replacement of a common strain with a less common one
Often due to successful vaccination against common strain
Herd Immunity
Vaccinate enough of population so that disease cannot spread
R: Transmission rate
Goal: R<1
Infected individual transmits to <1 person on average
Protects unvaccinated
Sequence the activation of the adaptive immune response.
- APC operates
- Helper T cells detect antigen
- B cells activated
- Antibodies released
- Reinfection triggers secondary response
