B cells Flashcards
what is key to clonal selection
each lymphocyte has receptors to only a single antigen
know clonal selection maps
see notes
main B cell funct.
make antibodies to mark things for detruction
what are steps to make an antibody
- mature B cell bind with antigen
- makes plasma cells
- creates antibodies to that path.
what is basic structure of antibody
1 heavy chain and 2 light chains variable region (Fab) and constant region (Fc)
4 functions of antibodies
- neutralization of toxins/bact
- opsinization
- activation of complement cascade
- help activate special cells
how does anti-body neutralize toxin/virus
binds to it so it cannot bind to cell receptor and enter the cell
how does antibody opsinize
Fab binds to bacteria and Fc binds to phagocytic cell and leads to phag of bact.
how does antibody activate complement cascade
classical pathway - C3 activation
what are antibody isotypes
different sublasses of anti bodies that have diff. functions and circulate in different areas
what is location and function of IgG
- small and all tissues
- opsinization and complement activation (C1)
what is location and function of IgM
- pentameric structure that is large and can’t leave blood
- binds strongly as first line and can also activate complement
what is location and function of IgA
- in secretions esp resp and intestinal tracts
- poor opsonin and weak complement activator
what is location and function of IgE
- trace amount in serum, most in mast cells under skin
- binding causes mast cells to degranulate leading to sneeze cough - involved in allergic rxns
how do B cells recognize antigen
with same imbedded immunoglobin that will become and antibody
what are 2 things B cell dev. must acheive
- large repetoire of antibodies
2. antibodies that can function in different ways (ISOtypes)
how does B cell gen diversity?
through recombining V,D,J in somatic recombination
what is light chain recombination steps
- germline DNA
- recombination
- VJ joined DNA
what is heavy chain recombination steps
- germlineDNA
- recombination
- DJ joined DNA
- recombination
- VDJ joined DNA
how does recombination control lymphocyte dev (2)
- allows progression to next stage
2. prevent further rearrangement allowing single specificity for each cell
where are 2 checkpoints in dev.
after heavy and light chain rearrangments
what happens if no receptor made?
apoptosis
where does rearrangment occur
bone marrow
what is product of rearrangment
immature B cell in bone marrow with IgM on surface
what is key life event of B cell
expression of IgM on surface
what is tolerance
only those B-cells that do not recognize self antigen are allowed to leave bone marrow
where does B-cell go after marrow
secondary lymphoid tissues
how does Bcell know where to go
chemokines
where does B cell go in lymph node
- to T cell area to look for antigen
2. if none move to B cell area in cortex
3 requirements for B cell activation
- cross-linking of surface imunoglobulin by specific antigen
- association of Bcell receptor with B cell co-receptor
- additional signal from helper T cell
what is T-cell help
- B cell links with T cell with same antigen spec.
- linkage causes T cell to release cytokines that activate B cell
- B cell become plasma cell
what happens when B cell meets correct T cell in node
- cognate pair travel to medularry cords
- undergo clonal expansion
- cause primary focus
what is primary focus
rapid early diff of B cells without T cells to create IgM as initial attack
what is secondary focus
movement of activated B cells out to form a germinal center
what is in germinal center (3)
- activated B cells
- T cells
- antigen
what occurs in the germinal center
rapid B cell prolif. leads to
- somatic hypermutation
- affinity maturation
what is affinity maturation
finds B cells that have strong affinity for antigen and brought to T cell for extra reproduciton
where does isotype switching occur
in the germinal center
what is isotype switching
original expression of IgM is changed to another type
how does isotype switching occur
due to recombination within the cluster of C genes
what are outcomes of B cells in germinal center (2)
- become plasma cell via IL-10
2. memory cell via IL-4
how to identify and lymphocytic leukemia
will all have the same Ig receptor on surface
how to identify myleloma (plasma cell)
will produce tones of same antibody
what antibodies are in the brain and a fetus
brain - none
fetus - IgG
what does IgA do
protects mucosal surface
what is IgA mechanism
- released from basement membrane and when bound is phagocytosed into cell and excreted into the lumen
- once in lumen it can help bind bacteria etc. in tract to can’t reporoduce and poo it out
what is ADCC
antibody dep. cytotoxicity - opsinize so binds with NK cells
how does C3b react with RBCs
- bound C3b binds with CR1 receptor on RBC
2. RBC carries it around until meets macrophage to take it off
how does allergy happen
mast cell response binds to non-threatening antigens via IgE causing reaction
what is anaphylaxis
make IgE to protein antigens such as peanuts and mast cell becimes coated
2. future contact leads to massive degranulation
what are autoantibodies
antibodies that recognize self - loss of tolerance
see conclusion slides
it will be helpful
