B - cells Flashcards
Define antigen and antibody
- Antigen – anything that can be bound by an antibody. Now antigens are also considered any substance that can induce an adaptive/acquired immune response. Antigens can be short peptides, proteins, sugars, lipids etc.
- Antibodies - are proteins produced by adaptive immune cells that bind specifically to relatively small parts of foreign molecules known as antigenic determinants or epitopes.
- Both antigens and antibodies are incredibly diverse
Define cytokine and chemokines
Cytokine - A general term to describe various small proteins secreted by cells that serve to regulate the immune system. Can also have effects on other cells in the body. Often called interleukins (ILs) i.e. IL-1, IL-2 etc.
Chemokines are a sub-type of immune molecules with involved in the movement and migration of immune cells.
What is Cluster of Differentiation?
- CD a historical term that was coined to define cell-surface molecules (generally proteins) on immune cells that are recognized by specific monoclonal antibodies. They are useful to identify cells but also have a function.
- The cluster of differentiation (CD) then received a number, for example CD1, CD2 etc., which stands only for the order of their discovery.
- Some CDs expressed on specific cell lineages i.e. CD3 is specific to T cells while others like CD11 others can be found on many lineages.
Compare and contrast the principles of innate and adaptive immunity
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What is the defining feature of innate immunity?
Not specific to individual pathogens. No memory persists after encounter.
What is adaptive immunity and what is the defining feature?
- A delayed but pathogen-clearing response.
- Usually increases in strength and effectiveness with each encounter.
- Component of the foreign agent (antigen) is recognised in a specific manner and the immune system acquires memory of it.
- Instructed mainly by 2 types of lymphocytes T cells and B cells.
- Defining characteristic: Immune response directed at specific pathogen’s antigen and memory persists after initial encounter.
What are the two different types of B cells?
- Produced in the fetal liver and produced antibodies in the absence of pathogens. They don’t require T-cell help.
- Bone marrow - They are produced in secondary lymphoid organs and circulate. They produce most of the high-affinity B cells. They require help of T-cells
In the spleen, they act as a first line of defence against bloodborne pathogens and may or may not require the help of T-cells
What is humoral immunity?
What is active and passive immunity?
Humoral immunity – immune response that takes places in bodily fluids
Humor = fluid
Following an infection the plasma contains substances - “antibodies (Ab)” - which neutralise that specific infectious agents or toxins.
Read through the cardinal features of the immune system
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What are the features of an antibody or Ig?
• Immunoglobulin glycoprotein Y-shaped Tetrameric • 2 identical heavy chains • 2 identical light chains • Held together by non-covalent interactions and by –S-S- crosslinks between cysteine
What can Ig be treated with to break the Ig into FAB and FC?
Proteases cleave them as the hinge regions.
FAB - Fraction antibody binding
FC - Fraction crystallisable
What is the function of the constant region?
Responsible for effector functions e.g activating complement or binding to phagocytes
How does an antibody bind to an antigen?
• Using non-covalent interactions
Electrostatic, hydrophobic, van der Waals forces, hydrogen bonds
Depends on the antibody binding site being exactly complementary, sterically (in space) and chemically, with a site on the surface of the antigen
The region on the antigen where the specific antibody binds is called an epitope or antigenic determinant
How does a B cell design a specific antibody to bind a specific antigen?
Randomly generates antibodies, with different antigen-binding sites due to Ig gene rearrangement, receptor editing, selection and somatic hypermutation.
PRODUCES IG RANDOMLY
Describe clonal selection and expansion of B-cells
- Multiple B cells with different B cell receptors
- Only one B cell receptor binds to antigen X and gets activated
- The antigen therefore selects the specific B cell clone which proliferates outnumbering the others
- Antigen X-specific B cell clones differentiate into plasma cells secreting soluble X-specific antibodies
