B-Lymphocytes Flashcards
BCR complex includes
BCR protein + CD79
BCR is…
membrane bound Ig that B cell releases when activated
CD79 function
signaling when Ags bind to membrane bound Ig
CD79 made of..
Ig-alpha and Ig-beta
Ig variable region genes form by
chromosomal rearrangements
Difference between B & T cell differentiation
Variable region mutations in B cells occur after activation.
T cells don’t have mutations in variable regions.
B-Cell Maturation occurs in
primary lymphoid tissues
primary lymphoid tissues
cloacal bursa, ileal Peyer’s patches, etc.
B-cell precursors made in
bone marrow & migrate
B-cell Maturation process
- Rearrange Ig variable region genes
- Express surface for of IgM
- Immature B cell tested for self-reactivity
Process of variable region gene rearrangement
Heavy chains rearrange 1st then light chains (either kappa or mu)
If immature B cells is self-reactive,
it may rearrange variable region genes again to test different Ig.
and then if STILL self-reactive, it dies!
If immature B cell isn’t self-reactive,
it co-expresses IgD & becomes a mature, naive B cell
B-Cell responses to Ags
Signal 1: Recognition
Signal 2: Activation
Signal 3:
B cell recognition
occurs without processing.
DIRECT recognition
Follicular DCs and macrophages
may hold Ags on their surfaces for B cell recognition BUT aren’t associated with MHC molecules
B-cell Activation Signals
delivered by Tfh cells using cell-cell contact & cytokines
B-cell’s respond to Ag in
SECONDARY lymphoid tissues
Tfh cytokines
activate B-cells & stimulate synthesis & secretion of Abs
T-independent Ags
Ags that deliver both recognition and activation signals.
repetitive ags that tend to have PAMP-like things incorporated in them (ie. LPS)
T-Independent Ags do NOT induce:
- Class switching (only IgM made)
- Somatic Mutations (Ab affinity doesn’t increase during immune response)
Effect of B-cell activation
B-cells proliferate, variable regions of Ig genes undergo somatic mutation, class switching occurs,
B Cell Proliferation occurs
in the germinal center
also called Germinal Center Reaction
Result of B cell proliferation
formation of secondary lymphoid follicles with germinal centers
Somatic Hypermutation
rapid mutations in variable region genes of proliferating B-cells
Effect of Somatic Hypermutation
changed affinity of BCR for antigen
Somatic Hypermutation to lower affinity
cells don’t compete well for available Ag.
eventually die because they don’t bind to Ag
Somatic Hypermutation resulting in higher affinity
compete effectively for available Ag.
Present Ag to Tfh cells, receive activation signals, proliferate and differentiate.
Affinity Maturation
the selection process, that over time, increases the affinity of BCR & antibodies
Class Switching
switching of Ag classes made during B-cell proliferation instead of the IgM that is initially expressed in mature B-cells
cell cuts off IgM gene via chromosomal rearrangement
DOES NOT change affinity b/c variable region genes don’t change
B-Cell differentiation
become (1) plasma cells or (2) memory cells
plasma cells
leave germinal center & secrete large quantities of Abs
memory B-cells
- remain in body for long periods of time
- lots have higher affinity for Ag than the first ones activated
- lots have class switched to IgG, IgA, IgE
Class Switching controlled by..
cytokines!
IL-4 induces…
IgE switching.
IgE involved in allergic reactions
What occurs when there is a high concentration of Ab in body?
plasma B-cells stop making & secreting Abs
plasma cell differentiation
doesn’t completely occur in germinal centers
Plasma Cell’s homes
medullary cords, red pulp, lamina propria, bone marrow (particularly IgG secreting ones)
