Adaptive Immune System- Focus On B Cells Flashcards
What is an antigen?
Any substance that can induce an adaptive immune response
Name a few things that antigens can be made up of
Short peptides, proteins, sugars, lipids and more
What is an antibody?
Proteins produced by adaptive immune cells that bind specifically to antigenic determinants
What is an antigenic determinant?
Relatively small part of foreign molecules that antibodies bind to
What is a cytokine?
General term to describe various small proteins secreted by cells that serve to regulate the immune system
How are cytokines named?
Often interleukin followed by a number but sometimes have other names linked to their function
What are chemokines?
The subtype of immune molecules that are involved in the movement and migration of immune cells
How do chemokines move cells?
Release chemicals in a gradient which guide the cells
What does CD stand for?
Cluster of differentiation
What is a CD?
Defines cell-surface molecules on immune cells that are recognised by specific monoclonal antibodies
What does the number after the CD stand for?
The order of its discovery
Do CDs have to be expressed specifically to one cell lineage?
No, can be found on many lineages
What is the defining characteristic of adaptive immunity?
Immune response is directed at a specific pathogens antigen and memory persists after initial encounter
What do lymphoid precursors do if they move into the thymus?
Mature into T cells
What do lymphoid cells mature into in the bone marrow?
B cells
What are the three large groups of B cell?
B1, B2 and regulatory B cells
Where do B1 cells mature?
In the liver
Where do B1 cells end up?
Peritoneum
Which immunoglobulin do B1 cells express on the cell surface?
IgM
What is the function of B1 cells?
Produce natural antibodies That are present in the absence of infection.
Do B1 cells require T cell help?
No
Where do B2 cells mature?
Bone marrow and spleen
What are the three types of B2 cell?
Follicular, transitional or marginal
Which is the most common type of B2 cell?
Follicular
Where are the follicular B2 cells located?
Secondary lymphoid organs (spleen, tonsils, lymph nodes)
Which type of B2 cell makes the majority of high affinity antibodies?
Follicular B2 cells
Do follicular B2 cells require T cell help?
Yes
Where are marginal zone B2 cells found?
In the spleen
What are the marginal zone B2 cells function?
First line of defence against blood-bourne pathogens
Do marginal zone B2 cells require T cell help?
May or may not
What is the function of regulatory B cells?
Produce responses that regulate the other two types
What are the three stages of primary adaptive response?
Activation, proliferation and memory cells
Why does the immune response decrease over time?
To maintain homeostasis
What is the significance of the antibodies being specific?
Makes sure the response to a microbe is directed at a particular antigen of that microbe
What is the significance of the antibodies being diverse?
The immune system is able to respond to a large variety of antigens
What is the significance of the antibodies doing clonal selection and expansion?
Increases the number of antigen-specific lymphocytes to keep pace with microbes
What is the significance of the antibodies being specialised?
Generates optimal responses against different types of microbes
What is the significance of the antibodies contraction and homeostasis?
Allows for recovery and to avoid collateral damage
What is the significance of the antibodies having a memory?
Increases the ability of the cell to combat repeated infections
What is the significance of the antibodies having a very low reactivity to self?
Prevents injury to the host
What are a lot of the symptoms of infection due to?
Collateral damage of the immune system and not directly related to the bug itself
What are Ig glycoproteins made up of?
tetrameric - 2 light chains and two heavy chains
How are the two light and two heavy chains held together?
Non-covalent interactions and disulfide cross links between cysteine residues
How are Ig glycoproteins shaped?
Y shaped
What is the fab fraction of the antibody?
Antigen binding bit
What can the Fc fraction of the antibody be used to create?
crystals
How are antibodies split into their Fab and Fc fractions?
Proteases cut the molecule at the hinge region
What is the function of the variable region?
To bind to the antigen
What is the constant region of an antibody responsible for?
Effector functions (activating complement, binding to phagocytes etc)
What is the idiotype?
The variable region tip
What is the isotype?
The Fc fraction and the bottom half of the variable region
What is the tip of the Ig variable region called?
CDRs- complement determining regions
How does an antibody bind to an antigen?
Electrostatic, hydrophobic, van der waals forces and hydrogen bonds
What is a linear determinant?
The Ig can bind to the determinant in both the native and denatured protein
What is a conformational determinant?
The Ig can only bind if the protein is folded
What are the two ways an antibody can be found?
The surface of a B cell or secreted from a B cell
How is an antibody attached to the surface of a B cell?
Anchored to the surface, with a TMD and a cytoplasmic tail
How does the body make millions of different B cells with different random antigen binding sites?
Ig gene rearrangement, receptor editing, selection or somatic hypermutation
How does clonal selection and expansion work?
Lymphocyte clones mature into generative lymphoid organs
Clones of mature lymphocytes specific for diverse antigens enter the lymphoid tissues
Antigen-specific clones are activated by antigens
Antigen-specific immune responses occur
Why are most antibody responses polyclonal?
More than one clone of B cells is generated or more than one Ig is synthesised
What are the 5 types of immunoglobulin isotopes?
IgG (gamma) IgA (alpha) IgM (mu) IgE (epsilon) IgD (delta)
Which Ig isotype has the most subclasses (and what are their names)?
IgG
1, 2, 3, 4
What is the Ig isotope that forms a pentameter?
IgM
Which Ig isotope dimerises?
IgA
What can the IgA dimer do that IgA on its own cannot?
Cross the muscosal barriers in the gut
What are the 6 antibody effector functions?
- neutralisation
- opsonisation and phagocytosis of microbes
- antibody dependant cellular cytotoxicity
- phagocytosis of microbes with complement fragments
- inflammation
- lysis of microbes
What are the two ways antibodies can opsonise a pathogen?
Neutralise it (bind to the toxin so they cant attack cells) Or bind to the antigens on the bacterial cell surface, which makes phagocytosis more efficient
