Adaptive Immunity II Flashcards
What are B cells
- communicate with T cells
- have a specific B cell receptor for antigens
- B cells produce antibodies
- clonal expansion leads to generation of two subsets
- plasma cells are great big antibody factories
- memory B cells are important
Where do B cells mature
Mature in bone marrow
Describe B cell circulation
Circulate in the blood and the lymph they are found in large numbers in the lymphoid organs
How do B cells recognise antigens
They recognise antigens through the B cell receptor (BCR) which is the actual antibody (lgM or lgD)
When B cells are activated what do they change into
Plasma cells - antibody factories
What are the three main receptors in adaptive immunity
- T cell receptor
- B cell receptor
- Major histocompatibility complex (MHC proteins)
Multiple genes encoding each allows the development of a repertoire of receptors with wide specificity
What are the 5 types of immunoglobulins produced by B cells
LgG, lgE, lgD, lgM, lgA
Describe the B cell receptor structure
Slightly different from T cell receptors, both have variable and constant regions, they have light and heavy chains
Describe LgG antibodies
Account for 80% of all antibodies, they are responsible for resistance against many viruses, bacteria and bacterial toxins
Describe lgE
Attaches as an individual molecule to the exposed surfaces of basophils and mast cells
Describe lgD
Individual molecule on the surfaces of B cells, where it can bind antigens in the extracellular fluid, this binding can play a role in the sensitisation of the B cell involved
Describe lgM antibodies
The first class of antibody secreted after an antigen is encountered. LgM concentration declined as LgG production accelerates, the anti-A and anti-B antibodies responsible for the agglutination of incompatible blood types are lgM antibodies
Describe lgA antibodies
Found primarily in grandular secretions such as mucus, tears, saliva and semen. These antibodies attack pathogens before they gain access to internal tissues
What is each development stage for B cells defined by
Defined by rearrangements of the immunoglobulin heavy and light chain genes
Once in periphery B cells migrate to…
Secondary lymphoid organs
Heavy B cell chains involves rearrangement of ….
Variable (V), Diversity (D) and Joining (J) genes
Light chain involves rearrangement of….
Variable (V) and Joining (J) genes
What is the B cell receptor
lgD
Immature B cell receptor is mainly…
LgM
Mature B cells express both….
LgM and lgD
Describe negative selection of B cells
Undergo negative selection in the bone marrow, macrophages will engulf and remove self reacting B cells
What are the three functions for antibodies in the human body
- Neutralisation
- Opsonization
- Initiation of complement
Primary goal is to prevent microbial activity and aid removal of threat from host
Describe opsonisation
Refers to coating of pathogens by antibodies or complement proteins
- phagocytosis
- antibody dependent cellular cytotoxicity (ADCC)
- mast cell degranulation
Describe complement initiation
Classical pathway - antibody attached to microbe
Describe B cell activation
- antigens require T cell help are called thymus-independent antigens
- occurs in lymph nodes
- activation of naive B cells results in the rise of plasma cells
- plasma cells are antibody factories
Describe B cell activation (T cell dependent)
T cell and BCR interactions requires co receptor binding (CD40 to CD40L)
- cytokine signals are released from T helper cell induce proliferation
- generates a pool of plasma cells which produce antibody
- also generates memory B cells
- plasma cells initially produce IgM before undergoing class switching
What is the first antigen produced after B cell activation and how many binging sites does it have
IgM and 10 binding sites
Why does class switching take place
Activation leads to class switching due to lgM response being weak therefore they class switch to IgG (or IgA/IgE)
This increases affinity for the antibody
What does avidity mean
Ability of antibodies to form complexes
Gives a measure of the overall strength of an antigen-antibody complex
In lymphoid organs cross talk between B and T cells leads to
- humoral immunity
- cellular immunity
What are germinal centres
Hubs for T cells and B cells to cross talk and
- proliferate and differentiate
- somatic hypermutation (class switching)
Describe vaccinations
B cells and T cells play a role in the process of vaccinations against a weak antigen, this leads to immunological memory, in the primary immune response IgM acts early but as B cells undergo class switching an IgG response follows
Presence of memory T and B cells means that upon second exposure the immune system can respond much faster
What is immunological tolerance
Sometimes the immune system can become dysfunctional and in a state of immune unresponsiveness to a particular antigen or set of antigens, two types central and peripheral
Describe Central tolerance
Can cause autoimmune disease something goes wrong in the selection of B and T cells
Describe peripheral tolerance of T cells
Not all self reactive T cells are eliminated however peripheral tolerance prevents their activation
Signal 1 but no signal 2 results in anergy
Signals 1 and 2 but no 3 (cytokine survival signal) results in deletion by apoptosis
T regulatory cells can also directly block activity by binding antigen (both self and foreign antigens)
Describe peripheral tolerance of B cells
- occurs in secondary lymphoid organs
- self reactive B cells still require help from self reactive T cells
- since most self reactive B cells do not receive any T cell help and therefore become anergic
Describe the term breach of tolerance
Breach of tolerance to self antigens or commensal organisms drives many autoimmune diseases
