B Cells Flashcards
What do B cells look like under the microscope?
Identical to T cells
Where are B cells produced?
Bone marrow
What do B cells have on their surface?5
Transmembrane BCR IG alpha and beta CD 19 CD20 CD40
Where do secreted antibodies come from?
Plasma cells
What are Ig alpha and beta?
Aren’t immunoglobulins
Used to send message to lymphocyte when ab meets ag
Markers for B cells
CD19 and CD40
Which immunoglobulins do naive B cells make?
IgM and IgD
2 regions of Ab- what do they do?
Variable and constant Variable binds to Ag Constant determines class of Ab
What kind of Ag do Abs recognise?
Native Ag
Structure of Ab:
2 identical heavy chains, 2 identical light chains
stretch of hydrophobic AA transmembrane
Short cytoplasmic chain
How many classes of Ab are there? how are they different?
5 classes - dif constant region eg IgM - mue C region (heavy)
Light chain constant is kappa or lamda eg IgM can have either kappa or lamda
Where does Ab variability come from? then?
Genetic recombination, then clonal selection
What is clonal selection + 3 stages:
Ag selects most appropriate B cell
Selective activation, clonal proliferation, differentiation to plasma or memory
What is somatic hypermutation?
Fine tunes Antibody - cells become quantitatively and qualitatively better during proliferation for secondary response
When do B cells class switch? what classes are there?
Once stimulated by antigen. IgM, IgG, IgA, IgD, IgE
How do B cells class switch?
Need help from Th2 cells - then mature to produce other classes
Interaction between naive B cell and Th2 cell: 4
B7 (Bcell) - CD28 (Th2),
CD40 (B cell) to CD40L (Th2)
MHC B cell to TCR
exchange cytokines
What does class of Ab depend on? example:
cytokines produced by Th2. eg IL4 and IL13 –> IgE
What happens after class switching?
Ag induced proliferation and somatic hypermutation of the new class’s V region
How do you get loads of mutations in somatic hypermutation?
No proofreading for V region, but regulatory regions that specify where to mutate
Cost of somatic hypermutation?
Not always good, can be poor affinity, moderate or good
What do you call it when there is even better binding after somatic hypermutation?
Affinity maturation
What happens to the Ab with bad hypermutation?
Die
Where does most of B cell proliferation happen?
secondary Lymph node
How can B cells act as professional APCs?
They grab the Ab and Ag and take it in,
Show it to TCR of T cell using MHCII (B7, CD40)
cytokines activate T helper cell
T cell independent Ags:
For some antigens - cross links so many so signal through Ig alpha and beta strong enough that no need for T cell help. eg polysaccharides Really good IgM but no class switching
How do Ig alpha and beta work?
have tyrosines on ITAMS - tyrosine kinases add phosphate to tyrosines
