B Cells Flashcards
What are B cells located
Developed in bone marrow and Thymus (primary lymphoid)
Activated in Lymph nodes and spleen (secondary lymphoid)
Where do B cells develop their receptors
In the bone marrow they build BCR
Describe the B cell receptors
2 heavy chains that embed in membrane and 2 light chains.
Membrane bound when B cell - excreted by plasma cell and become antibodies
How do B Cell Receptors (BCR) work
Bind directly to specific antigen and activates B cell - surface covered in lots of receptors
How are antibodies released
When the B cell becomes a plasma cell it secretes the receptors which become antibodies
What are the 3 functions of antibodies
NOC
Neutralisation
Opsonisation
Compliment activation
Describe Neutralisation
Antibody binds to surface of virus, covering it.
Stops it from binding to other cells/infecting them
Describe Opsonisation
Antibodies are specific to pathogen - they bind to Bacterium and indicate to phagocytes that it needs to be dealt with (easier to recognise)
Describe Compliment activation
Antibody give a site for compliment to bind to to form Membrane Attack Complexes
What thing need to be considered as to which antibody (isotype) to use
Different pathogens (specific receptors)
Different sites of the body (mucus layers, tissue)
Replicating pathogen
Describe IgM antibodies and when used
Pentamer
Membrane bound to naïve B cells.
First produced after initial exposure.
What are the functions of IgM antibodies
Effective at activating compliment.
Extracellular bacteria
Acts as antigen receptor (BCR)
Describe IgG antibodies and when used
Monomer
Most abundant antibody
In blood
What are the functions of IgG
Opsonises/neutralises
Crosses placenta - provides passive immunity to baby
Virus/bacteria
Describe IgA antibodies and when used
Dimer (two antibodies joined by J chain)
Secretions (tears, saliva, mucus, breast milk)
Adapted to mucus with secretory component
Monomeric in blood
