Naive B cells
2 membrane bound immunoglobins that act as antigen receptors
IgM and IgD
But cannot produce antibodies
Humoral immune response
Naive BLCs recognize antigens, but not produce antibodies until they are activated and differtiated into plasma cells, producing antibodies
Plasma cells do not express antibody receptors anymore, only produce them
Number of B-cells
1 activated B-Cell can produce thousands of plasma cells and these can produce thousands of antibodies per hour
What is heavy chain isotope switching?
B cells produce antibodies with different heavy chain isotopes with different effector function for different microbes
Affinity maturation?
Repeated exposure to an antigen
-> antibodies will increase their affinity for the antigen
Affinity def:
Follicular B cells
Reside around the follicles of lymphoid organs
makes most T-dependent antibodies
Protein antigens -> processed by APC and recognized by CD4+ (CD4 imp. Role in activation of these B lymphocytes)
Show more class switching + higher affinity responses -> long lived plasma cells
B-1 cells
Respond to nonprotein antigens in mucosa
Make natural antibodies: produced spontaneously, not for immune reaction but imp. For clearing apoptotic cells
B-1 / marginal zone B cells
Make T-independent antibodies
non peptide antigens stimulate antibody production without need of T-cells
Much more simple
Secondary Humoral response?
Has shorter response time + higher number of antibodies
Higher affinity (affinity maturation)
More IgG (also IgA and IgE) due to heavy chain isotope switching due to increased amount of helper T cells
Important terms of Stimulation of B lymphocyte by antigen
Cross linking
BCR complex
Reqiured for B cell activation -> activation of more then one antigen receptor
can be several antigens binding in an aggregate or an antigen with several identical epitopes
Polysaccharides/lipids often have several epitopes, proteins might bind in clusters to initiate cross linking
= Receptor + Igalpha +Igbeta
usually IgM or IgD act as B-Cell receptor on naive cells (Not able to transducer signal
Igalpha and Igbeta proteins transduce the signal (similar to zeta and CD3 in TCR complex)
Functional consequences of B Cell activation by antigen (5)
Increased survival and proliferation
By expression of proteins that promote survival and cell cycling
interaction with helper T cells
By antigen presentation, increased B7 expression
Responsiveness to cytokines
By increased expression of cytokine receptors
Migration from follicle to T cell zone
Increased expression of CCR7
Antibody secretion
Generation of plasma cells
Has the innate immunity a role in B cell activation?
Yes sir,
B lymphocytes express a receptor for a protein of the complement system that provides signals for activation for these cells
C3 complement protein (most abundant protein) coats the microbe as the complement system is activated
CR2 receptors on B cells (coupled with CD19 and CD81) Recognises C3 -> leads to activation
CR2 is coupled with?
And which contains ITAMs?
CD19 and CD81
CD19 contains ITAMs
TLR receptors on B cells?
B cells also express TLRs
They recognize PAMPs directly and send activation signals
No itams here
T-B cell interaction
Where are Naive CD4+ T cells activated?
Where are naive B cells activated?
CD4+ cells activated in T cells zones
B cells in follicles by the same antigen
-> then they migrate toward each other and interact at parafollicular area
Which enzyme converts cytosine into uracil in isotope class switching?
AID(activation induced deaminase)
Activated by CD40 signals
Antibody feedback?
A specific mechanism for shutdown of antibody production
Circulating IgGs still bind antigens in blood and B cells specific for this may bind this complex
The Fc tail of IgG will bind to specialised Fc-Receptor on B Cell Fc-gamma-R2B
This receptor delivers inhibitory signals
Inhibits excessive antigen production
Last changeda year ago