Immunology - Humoral and Cell-Mediated Immunity Flashcards
What mediates humoral immunity?
Antibodies
What are the 2 regions and their roles in antibodies?
Fab region - Antigen binding
Fc region - Antigen elimination (binds Fc receptors)
Explain the 4-chain structure of antibodies
- What 2 types of chains make this up?
- Molecular weights (kD)
- What joins these chains?
Light (L) chain - 25kD
Heavy (H) chain - 50kD
2 Heavy chains and 2 Heavy chains
- Joined by S-S bridges
Which regions within antibodies are variable and constant?
- Role and traits of variable and constant regions
Variable (V) region - Bind antigen; Differ between antibodies with different specificities
Constant (C) region - Same for antibodies of a given H or L chain class type
What encodes Variable and Constant regions?
How can new specificity be achieved?
These regions are encoded by separate exons
Multiple V region exons can recombine during B cell differentiation to give rise to new variable region and specificity
What are the 4 understood Immunoglobulin classes?
- What is each important in?
What structural feature sets each class apart?
They all differ in the amino acid sequence of the heavy chain
IgG (γ) - Main class in serum and tissues; Secondary response
IgM (µ) - Primary response
IgA (α) - In serum and secretions which protect mucosal surfaces; Secretory component protects them proteolysis
IgE (ε) – Very low concentrations; Allergy and protection against large parasites
What are the 2 light chain types?
- Give 2 examples of a nomenclature of an antibody including light chain type
Kappa (κ)
Lambda (λ)
e.g. IgGκ, IgGλ
Characteristics of a primary and secondary response?
Primary - Slow and small response of antibody production
Secondary - Very rapid and massive production of IgG
Explain class switching in secondary response and how it provides flexible response?
B cells can switch from IgM to IgG, IgA or IgE after antigen stimulation depending on type and route of infection
Same V region gene recombines with different C region genes
- Same antigen specificity linked to different Fc functions
This all allows for flexible response Flexible response
Distribution of 4 Immunoglobulin classes in the body?
- One has 2 types with different distribution
IgG - Serum and extracellular blood; Can cross placenta
IgM - Usually restricted in blood
IgA monomer - Blood and extracellular fluid
IgA dimer - Mucosal secretions, saliva, breast milk
IgE - Mainly associated with mast cells beneath epithelial surfaces e.g. Respiratory tract
What is affinity maturation?
- How does this happen? (2 ways)
- Somatic hyperstimulation of V region genes in B cells responding to antigen
- Mutations increasing binding affinity are selected
Effects of all Immunoglobulin classes on pathogens? (3 effects)
Complement mediated lysis (bacteria and enveloped viruses)
Enhancement of phagocytosis (opsonisation)
Enhanced killing of infected cells by NK cells
Specific effects of IgA on pathogens? (3 effects)
- Specify monomeric, dimeric or both
Block adherence
Neutralise toxins
Agglutination of bacteria, inhibiting movement (dimeric IgA)
Specific effects of IgG on pathogens? (3 effects)
Block adherence
Neutralise toxins
Block uptake of nutrients
Specific effects of IgM on pathogens? (2 effects)
Block adherence
Agglutination of bacteria, inhibiting movement
How do antibodies activate complement (“Classical Pathway”)?
- Why is IgM better than IgG at activation
C1q interacts with 2 Fc regions
- IgM (pentamer) better activator than IgG
Activation leads to opsonisation, inflammation and cell lysis
How do antibodies like IgG and IgA monomer act as opsonins?
They bind bacterial Fc receptors and direct pathogen toward the Fc receptors on phagocytes
What do infected host cells express on their cell surface?
How can NK cells take advantage of this?
This is called ADCC, which means?
Infected host cells express foreign proteins on their cell surface (e.g. virus envelope proteins)
Allows specific recognition by NK cells with appropriate receptors; These then induce apoptosis
This is called Antibody Dependent Cell-Mediated Cytotoxicity (ADCC)
How does the Thymus influence things like class switching and B cell response?
- Name of antigens?
What is the name of antigens which are not influenced by the thymus?
B cell response and class switching require T cell help; These are matured in the Thymus
- Thymus-dependent
Thymus-independent (TI) antigens; Induce B cell response in absence of T cells
Which lymphocytes mediate Cell-Mediated immunity?
Traits of these lymphocytes?
T cells
Mature in Thymus
Bind antigen through specific T cell receptors
What are the 2 major subpopulations of T lymphocytes?
- Receptor type
- Roles of each
T Helper Cells (CD4 +ve)
- Help B cells make antibody
- Activate macrophage and NK cells
- Help development of cytotoxic T cells
T Cytotoxic Cells (CD8 +ve)
- Recognise and kill infected host cells
What is a TCR and what part of an antibody is it similar to?
- What happens with exons like they do in antibodies?
T Lymphocyte Receptor (TLR) is similar to antibody Fab arm
- Exons which encode V region recombine during T cell differentiation (somatic recombination)
How do T cells recognise antigen?
- How does this differ to B cells
What is an APC?
T cells can only recognise host cell-associated processed antigen
- Unlike B cells which can recognise free antibody
APC - Antigen Presenting Cell
What is the MHC and what does it do?
Which cells express MHC I and II and what do they both do?
Major Histocompatibility-Proteins (MHC) – Transports processed antigen to the surface of host cells
MHC I - Expressed by all nucleated cells; Display ENDOgenous peptides to CD8 +ve (type?) T cells
MHC II - Expressed by Macrophages, Dendritic (very specialised) cells and B cells; Display EXOgenous peptides to CD4 +ve (type?) T cells
