B Cells And Antibody Flashcards
Outline B cells
Are lymphocytes that develop in bone marrow (complete maturation within bone marrow)
Express unique antigen receptors (BCR or secreted antibody)
Plasma cells are activated B cells that secrete antibody
Memory B cells provide memory
Outline the origin and maturation of B and T cells
Both B and T lymphocyte precursors originate in bone marrow
Lymphocyte precursors destined to become T cells migrate (in blood) to the thymus and mature there. B cells mature in the bone marrow. During maturation, lymphocytes develop immunocompetence and self tolerance
Outline the structure of Antibodies
2 identical light chains, and two identical heavy chains
Antigen binding sites on Y ends, and transmembrane region at single end
Outline B cell receptors
The surface of each B cell is covered with approx 100,000 BCR (mainly IgM/IgD antibodies)
The BCR binds antigen and activates B cell (also need CD4 cytokines)
BCR is membrane anchored via a transmembrane domain. Secreted antibodies lack a transmembrane domain
What are the three functions of antibody
Neutralisation - binding viral protein, blocking interactions
Opsonisation - tastier to phagocytes/easier to phagocytise
Complement activation
What is viral neutralisation
Antibody binds virus and blocks viral protein/host interaction
What is opsonisation
Antibody binding bacterium makes more tasty/desirable for phagocytes. Phagocytes have antibody receptors
Outline activation of complement system and pore formation with antibody
Antibody bound microbe surface stimulates complement protein formation. Complement proteins form membrane attack complex, which in tern perforates foreign cell leading to cell lysis and death
Outline class, distribution, and function of IgG
Class of immunoglobulin (antibody).
Most abundant Ig class in blood - produced by B cells, circulates long period of time.
Functions - opsonisation/neutralisation. Only Ig class that crosses the placenta: provides passive immunity. Targets virus/bacteria
Outline the class, distribution, and function of IgA
Class of immunoglobulin (dimeric consists of secretory component and J Cain)
Distribution - present in secretions such as tears, saliva, mucus, and breast milk. Is monomeric form in blood.
Function - defence of mucous membranes, esp gut. Present in Brest milk. Confers passive immunity to nursing infant. targets virus/bacteria
Outline the class, distribution, and function of IgM
class of immunoglobulin (expressed monomeric form on naive B cell surface, pentameric form in blood stream)
Distribution - first Ig class produced after initial exposure to antigen. Expressed on naive B cells
Function - very effective in activating compliment (best antibody for compliment activation). Targets extracellular bacteria. Acts as antigen receptor (monomeric form on B cell surface)
Outline the class, distribution, and function of IgE
Class of immuno globulin (antibody) produced by B cells
Distribution - present in low blood concentrations
Function - Immunity to multicellular parasites. Allergic reactions
IgE activates mast cells (produce inflammatory mediators e.g. histamine) for parasite immunity and the allergic response
Outline the class, distribution, and function of IgD
Class of immunoglobulin (antibody)
Distribution - Expressed on naive B cells
Function - together with IgM, acts as B cell antigen receptor. Specific function unknown
What causes the formation of plasma cells
Stimulation of B cells by antigen + T cell leads formation of plasma cells
What part of antibody differs between antibody
The bottom, constant region. Region not in contact with antigen. Determines the mechanism used to destroy antigen, but not the antigen that it targets
Outline 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 - antibody secreting cells
Outline the primary immune response
Takes around 7-14 days before sufficient antibody os produced to eliminate pathogen (full sterilising immunity)
Relatively low amount of antibody produced - mainly IgM (activating compliment)
Outline secondary immune response
Basis of success of vaccination
Relies on memory B cells
Fast: 2-3 days, sufficient antibody is produced to eliminate pathogen mainly IgG (better all function antibody, also opsonisation), with additional class switching to IgA and IgE
Why do the classes of produced antibodies different throughout an immune response
Different classes of antibody produced as B cells matures and determines better antibody res once
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 most effectively activates compliment 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
The process of coating a microbe in antibody or compliment is called…
Opsonisation
The primary immune response is characterised by the production of predominantly…
IgM
The most abundant Ab isotope produced during the secondary immune response is…
IgG
Do memory B cells express BCR and secrete antibody
No. Memory cells only express BCR. They do not secrete antibody
Which of the following is true for plasma cells:
Can become memory B cells. Are derived from T cells. Possess a BCR. Secrete antibody
Plasma cells can secrete antibody
Only B cells specific for tetanus toxin would undergo clonal expansion during an immune response to TT because
They bind native TT and present a peptide from TT to Ag-specific CD4 T cells
