Thrush - B cell activation Flashcards
B cell dev is divided into two major phases:
- Ag independent phase: takes place in BM. Noted by Ig gene rearrangement
- Ag - dependent phase: upon recognition of Ag, B cell: proliferates, becomes plasma cell/memory cell –> class switches
Describe B cell development
- Ag independent phase: Ig gene rearrangement = Ag specific B cells.
- movement to periphery: contact Ag, then proceed. 90% B cells die; self reactive cells apoptose –> clonal deletion.
- Ag dependent phase: Along with T cell help, B cells will dev into plasma cells or memory cells and can class switch
what are classic B cell markers
CD19, CD20, CD45R
A ___ cell is not committed to becoming a B cell.
stem
___alpha and ___ beta are signaling molecules for antibody.
Ig; Ig
What do the pro- B cell consist of
- heavy chain rearrangement
- CD19, CD20, CD45R
- Igalpha, Igbeta
- RAG/1 RAG/2
- Tdt expression
what does the pre-B cell consist of
Heavy chain with surrogate light chain on B cell surface
*no Tdt expression
describe membrane expression
surrogate light chain allow heavy chain to go to surface of B cell. When they interact with bone marrow stromal cells. Ig alpha and Ig beta go in and tell them to start light chain
what is receptor/light chain editing
an attempt to make a self reactive/bad Ab into a good one.
____ B cell is the one that expresses IgM and IgD and begins Ag ____ phase and B cell activation
Mature/naive; dependent
After Ig heavy gene rearrangement, it associates with ____ ____ chain and binds stromal cell marker, then ___ stop and light chain starts. It cannot rearrange other H- chain alleles. This is known as ___ ____
surrogate light; IgH; allelic exclusion
In bone marrow B cell isn’t there by itself. Its also interacting with ____ cells
stromal
Without Ag stimulation B cell will die. _____ ______Ags need T cell help
Thymus dependent; with the help of cytokines and other proteins
Thymus independent Ags are divided into two types:
TI-1: bacterial cell wall components (LPS); not Ag specific; polyclonal B cell activators.
TI-2: repetitious cell wall components (polysaccharides); Ag specific!
What are two signals for B cell activation
- Ab binding to Ag: need crosslinking of mIg; single epitope Ags are not effective. Need Igalpha and beta to send signal to nucleus.
- CD40 interacting with CD40L which is on T cells which means they have been activated too.
- Cytokines can also serve as 2nd signal
____sends second signal to B cell to help activate it
CD40
Ig alpha and Ig beta are responsible for _____ to be phosphorolated which causes a signaling cascade. Signaling results in changes in gene expression
ITAM = immunoreceptor tyrosine based activation motif
____ is the ligand binding domain and the signal transducing molecules
BCR
When CD21 binds to ____ it causes a conformational change to CD21 which causes CD19 to send a signal to activate B cell. ____ sends a negative signal to the B cell and is considered a ____
C3d; CD22; ITIM
Summarize B cell activation
- Ig binding to Ag causes crosslinking. You get Igalpha and beta signaling as well as CD40 and CD40L, or CD19 and 21 if complement proteins are present.
- Then you get changes in gene expression.
- Internalization of Ig/Ag complex to destroy it.
- Ag presentation to T cells then you get more co stimulation of B cell cell
- B cell differentiation: class switching, memory cell and plasma cell production
What are two signals that T cells need.
- TCR- Ag/MHC
2. CD28 - B7
___ is present when you get a switch to IgE
IL-5
What are unusual B cells. Where are they located?
B1 B cells that express CD5 on their surface. They have limited diversity. Then tend to use V region genes closes to the D locus at the end. They have a few choice to use. They are in pleural and peritoneal cavities. They have low affinity and high rate of cross reactivity (polyspecificity). They usually bind to polysacchrides. They dont class switch or have T cell help and self proliferate in periphery without Ag stimulation and are likely to dev into cancer.
what is a T cell marker
CD5
Abs from B1 B cells often called _____ antibodies.
natural
What is the effector function of the B cell of the antibody?
- Primary response: when a naive B cell first sees its Ag: characerized by IgM production, slower response, during/after this response, B cells class switch, doesnt have to have T cell help but it works better with it.
- Secondary response: Memory response; production of IgG or other isotypes; affinity maturation; quicker response; needs T cell help
where is B cell getting activated
Lymph tissue/ lymph nodes
where is the area where mature B cell development occurs
germinal center
____ dendritic cells trap antigen but dont internalize it. Its not a traditional antigen presenting cell bc they dont express MHC class II
Follicular
What are Ig/Ab functions
- Pathogen neutralization
- Complement fixation
- antibody dependent cellular cytotoxicity
- opsonization
- inflammation