8 B Cell Mediated Immunity I Flashcards
What is the signal transduction unit of the B cell receptor (BCR)?
IgAlpha and IgBeta complex crosslinking
What is the co-recptor for the BCR?
Complement Receptor 2 (CR2) binding to C3b
What signals are required for B cell activation?
BCR
CR2
T cell help
What is the difference between Thymus Dependent and Thymus Independent Antigens?
Dependent Antigens need Costimulation by Helper T cell to activate B cells
Do B cells and T cells that are in the Germinal center reaction have to have the same antigen to activate them?
No, they can be activated by different antigens
What two ways do TI antigens overcome the need for T cell help?
1. TI-1 Antigens:
Stimulate via different route:
Engage BCRs as well as PRRs
these are known as "mitogens"
2. TI-2 Antigens:
Heavily crosslink BCRs
these usually respond to cell wall partsWhat do B1 cells respond to?
Cell wall polysaccarides
What do mitogens activate?
Both BCRs and PRRs to activate B cells without T cell costimulation
What are Infants and Toddlers unable to make that limit their response to cell wall antigens?
B1 B cells
What type of activation of B cells do high concentration of TI-1 antigens illicit?
Polyclonal (not monoclonal) expansion and non-specific antibody response
What type of activation of B cells do low concentrtion of TI-1 antigens illicit?
Antigen specific response, usually via IgM production
What are the limitations of Thymus Independent (TI) responses?
Nonspecific No class switching No Memory (so each response will have to start over) B cell response never changes
What type of antigen can infants and toddlers not respond to?
TI-2 antigens
usually cell wall components, crosslink BCRs
Where do germinal center reactions occur?
Lymphoid follicles of secondary lymph (nodes)
What happens in the germinal center?
somatic hypermutation
class switching
cytokine production
What is an overview of B cell activation in the germinal center reaction?
- Antigen-specific B cells enter the T cell zones
- B cells interact with antigen-activated Th2 cells to form a primary locus
- Germinal center reaction (positive selection and monoclonal expansion)
- Plasma (early) and Memory (late) Cell production
What are Follicular Dendritic Cells?
Use complement and antibodies to pick up antigens to present Do not use MHC class II Antigens Not APCs Like a buffet of antigens
What does IL 5 induce in class switching in B cells?
IgA class switching
What does IL 4 induce in class switching in B cells?
IgE class switching
What is virtually the only thing a Plasma Cell is used for?
Antibody production 30-60 days post infection
What antibodies are found in the blood?
IgG
IgM
IgA
What antibodies are found in the mucus?
IgA
Where is IgE found?
Mast cell FceRI receptor in skin, BALT, GALT
How do multimeric Igs enter the tissues from blood?
Poly-Ig receptor and transcytosis
How do IgGs enter the tissues from blood?
Brambell receptor and transcytosis
How do IgGs enter the placenta?
Brambell receptor (FcRn)
What Ig is associated with crossing the placenta?
IgG
What are examples of passive transfer of immunity?
Injection of antibodies
Maternal Ig’s via breast milk and placental barrier on Brambell receptors
What fetal Ig is at the same concentration as maternal?
IgG
What Ig is secreted in breast milk?
IgA
How does the Ig of breast milk enter the tissues?
Poly-Ig Receptor
When does infant IgM kick in?
5-9 months
When do IgG and IgA kick in?
1 year to high levels
What Fc Receptors were highlighted in lecture?
FcEpsilon Receptor: Binds IgE in mast cells
FcyReceptor III: Bind IgG1
Induce NK cells and APCs
What do Ig’s need to be active? Exception?
Antibody needs to be bound
FcEpsilon is the exception (binds IgE free in blood to highjack for Mast cell use as antigen receptors)
What WBC targets parasites coated with IgE?
Eosinophils
