B cells and Antibody Flashcards
Where do B cells develop?
B cells are lymphocytes that develop in bone marrow
Unlike T cells they completely mature in the marrow
What do B cells express?
Unique antigen receptors from B cell receptors (BCR) or secreted antibody
What are plasma cells in relation to B cells?
Plasma cells are activated B cells that secrete antibody
Secreted antibody is very soluble protein
Antibody floats around in plasma cell until required
What do memory B cells do?
Memory B cells provide memory
Allows body to recognise antigens and prevent infection
What happens when BCR sense antigen?
When sense antigen B cells divide and produce plasma cells and memory cells
What is the basic antibody unit composed of?
2 identical heavy and 2 identical light chains
What is the BCR?
The surface of each B cells is covered with ~ 100,000 BCR (mainly IgM/IgD antibodies)
The BCR binds antigen and activates the B cells
BCR is membrane anchored via a transmembrane domain (TM). Secreted antibodies lack a TM (lost by mRNA splicing)
What are the three functions of antibody?
Neutralisation
Opsonisation
Complement activation
What is neutralisation in regards to antibody?
Antibody binding to a virus protein that can block interaction of virus and host cells (can also happen in toxins)
What is opsonisation in regards to antibody?
Antibodies binding to surface of macrophages
Easier for macrophage to phagocytose antibody as has specific receptors
What is complement activation in regards to antibody?
Activation of complement system and pore formation
Complement proteins form membrane attack complex which results in pores in cells allowing flow of water and ions in and out of cell
What is IgG?
Monomer
Most abundant Ig class in blood
Opsonises/neutralises
Only Ig class that crosses placenta : provides passive immunity to unborn child
Targets virus/bacteria - great neutralising antibody enlists help of phagocytes
What is IgA?
Dimer
Has a J chain
Present in secretions such as tears, saliva, mucus and breast milk
Monomeric form in blood
Defence of mucous membranes especially in gut
Confers passive immunity on nursing infant
Targets virus/bacteria
What is IgM?
Pentamer
First Ig class produced after initial exposure to antigen - present at start of immune response
Expressed on naive B cells
Very effective in activating complement
Targets extra cellular bacteria
Acts as antigen receptor (BCR)
What is IgE?
Monomer
Present in blood at low concentration
Immunity to multicellular parasites
Allergic reactions (e.g. pollen or penicillin)
IgE activates mast cells for parasite immunity and the allergic response
What is IgD?
Monomer
Expressed on naive B cells - produced as mixture of IgD and IgM
Together with IgM acts as antigen receptor
Specific function unknown
What are the memory responses of B cells?
Stimulation of B cells by antigen +T cell leads to formation of plasma cells
What are memory cells in regards to B cells?
Memory cells persist for years in blood and lymphatic tissue
Express antibody as BCR but do not secrete antibody
Respond rapidly to antigen encounter and become plasma cells
What are the primary immune responses for B cells?
Takes around 7-14 days before sufficient antibody is produced to eliminate pathogen
Relatively low amount of antibody produced - mainly IgM
What are the secondary immune responses for B cells?
Basis of the success of vaccination
Relies on memory B cells
Fast: 2-3 days, sufficient antibody is produced to eliminate pathogen - mainly IgG with additional class switching to IgA and IgE
The antibodies important in providing passive immunity to infants are?
IgG and IgA
The antibody responsible for allergy is?
IgE
The first antibody secreted after initial antigen exposure is?
IgM
The antibody that most effectively activates the complement system is?
IgM
The antibody that most effectively destroys multicellular parasites is?
IgE
The BCR on naive B cells is mainly composed of?
IgD and IgM
B cells recognise _____ via their ______, while T cells recognise ______ in the context of _____
Native antigens
BCR
Peptides
MHC
