Chapter 10 - I Flashcards
B cell Activatoin
BCR has similarities to TCRs
Unlike T cells, B cells can make secreted forms of their BCR –> antibody
– their whole point is to secrete antibodies
B cells can respond to antigen in a T independent or T dependent manner
- With or without help of TH
cells
This is determined by the chemical nature of the antigen itself that is recognized by B cell’s BCR
B cell activation by T cells
THe type of antigen determines whether B cell is activated by T cells or independent of T cells
T- Independent B cell Activation
Antigens for T independent B cell activation: - Structure with numerous repeating units - Eg. polysaccharide capsules of some bacteria
T independent Responses - Relatively fast because TH cells aren't involved - result in low-affinity IgM antibodies and no immunological memory - However, may be sufficient to provide immunity
Some vaccines induce T independent responses - not great
T- dependent B cell Activation
Antigens for T dependent B cell activation: - Have protein component (could be entirely or partly protein) - the protein is processed and displayed on MHC class 2 proteins (for TH cells) - TH cells then help B cell: need TH cells because number of BCR that get linked is less
T- dependent Responses: - Slow due to involvement of TH cells - result in high-affinity class- switched antibodies (IgG, IgA) and immunological memory
Some vaccines induce T dependent responses
Why do some antigens need TH cells to assist B cell activation and other antigens don’t
Number of BCRs that get cross linked
B cell Activation - Signal 1
T dependent
Also need 3 signals like T cells
Signal 1 is the binding to the unprocessed, intact antigen to 2 adjacent BRCs –> cross-linking the BCRs together
the signal is relayed to the nucleus by Iga/Igb co-signaling molecules
Both variable heavy and light regions of the immunoglobulins participate in the binding of the antigen
Antigens makes it way to the lymph node or spleen where the B cells are hanging out
B cell Activation - Signal 2
In order to receive signal 2, B cell must find some way of identifying itself to TH cells that it needs help in the binding of the antigen
Does this by endocytosing the Ag-BCR complex into the cells by an endosome, processing it, and displaying a peptide on the MHC class 2
** The B cell is acting as an
APC so that it can get hep
from TH cell
The TH cell was previously activated by the dendritic cell with the same antigen (cuz same timeline, same infection/invasion)
In the lymph node/spleen, the B cell finds the activated TH cell
Signal 2 is the binding of CD40 on the B cell to CD40L on the TH cell
B cell Activation - Signal 3
Signal 3 is the cytokines secreted by TH cells that help support division and differentiation into effector plasma B cells (that secret antibodies), or memory B cells
B cell Differentiation
TH cells that help support division and differentiation into effector plasma B cells (that secret antibody), or memory B cells
The secreted Ab last a few months in the body
The plasma cells can live a few months - unless they get back to bone marrow - live years
Memory cells are ling lived (years)
For T independent responses, we get short-lived plasma cells and no memory cells
For T-independent responses, B cells only receive signal 1 then starts proliferating right away
How is the development of memory B cells important in immune response
- Memory B cells response faster to antigen - the differentiate into plasma cells within 2-3 days (instead of 10 days for naive B cells)
What medical procedure exploits immune systems ability to have memory responses
Vaccination
What is a nuisance
Allergies, autoimmune disease
