Humoral Immunity Flashcards
B cell receptors are ____.
Antibodies
Which type of antibody is MOST important?
IgG - has the broadest functions
The first antibody active in the adaptive immune response is…
IgM
All mature B cells display ____ on their cell surfaces.
Antibodies
When activated, B cells can differentiate into ____ which secrete soluble ____.
When activated, B cells can differentiate into PLASMA CELLS which secrete soluble ANTIBODIES.
What are the three main functions of antibodies?
1) Neutralization of the pathogen and its toxins
2) Opsonization - tagging of bacteria for phagocytosis
3) Activation of complement - via classical pathway, whereby C1 binds to Ab-coated pathogens
Bonus: ADCC (NK cells and eosiniphils)
What is antibody-dependent cell-mediated cytotoxicity (ADCC)?
- Facilitates NK response to viruses
- Also facilitates eosinophil response to parasites
- When Abs bind to the pathogen, immune cells recognize the Ab
- This cross-linking signals for the immune cell to attack the pathogen
Describe the structure of antibodies.
- 2 heavy chains and 2 light chains
- Heavy chain is the constant region and determines the class/isotype
- Both heavy and light chains form the variable region, which determines the antigen binding site
Diversity of antibodies and the variable region is achieved via…
Somatic recombination (VDJ rearrangement)
Immature B cells display ___ antibodies on their surfaces.
IgM & IgD
Junctional diversity is generated by the addition or deletion of ____ during somatic recombination.
Single nucleotides
What is affinity maturation?
- Also called somatic hypermutation
- Occurs AFTER B cell activation by antigen
- Clones will have point mutations in the antibody V-region genes - this variability could allow for some clones with increased affinity for the antigen
What is isotype class switching?
After B cell activation, the heavy chain of antibodies can change to allow for class switching
The first antibodies to be secreted by plasma cells are…
IgM
AID is an enzyme that assists with…
Somatic hypermutation and isotype class switching
What are three requirements for B cell activation?
1) Encounter the specific antigen that will bind the antibody (BCR)
2) CD40L on T cells binds to CD40 on B cells
3) Activation from cytokines produced by T cells
Do B cells ALWAYS need T cells to become activated?
No - some antigens are capable of initiating an antibody response independent of T cells
How do B cells find their corresponding T cells?
- B cells can endocytose pathogens and load peptides onto MHC molecules
- Peptide-MHC complexes on the B cell surface
- T cells that recognize and bind to the specific peptide-MHC complex will release cytokines and bind to CD40 via CD40L to activate the B cell
Describe central and peripheral tolerance.
During B cell development, B cells are tested for autoreactivity before they leave the bone marrow (central tolerance) and again in the periphery (peripheral tolerance).
