Humoral immunity Flashcards
Effector functions of antibodies
Pathogen and toxin neutralisation
Classical complement activation
Opsonise - promotion of phagocytosis and pathogen elimination
Where do B cells develop
Develop and mature in bone marrow
During foetal stages
How many types of B cell are there
10 million different types
What is B cell receptor
Transmembrane protein
Composed of a membrane-bound immunoglobulin molecule and a signal transduction
How does antibody production occur
Antigen recognition by BCR
Activates B cell
B cell proliferates and differentiates
Produces plasma cells which secrete antibodies
Can also make memory cells which remain in extracellular fluid in case of reinfection
Other names for antibodies
Immune globulins
Immune serum globulins
Gamma globulins
What is the difference between antibodies and immunoglobulins
All antibodies are immunoglobulins but all immunoglobulins are NOT antibodies
Immunoglobulins are attached to B cell membrane while antibodies float in circulation
What are the 5 classifications of antibodies
Immunoglobulin A Immunoglobulin G Immunoglobulin M Immunoglobulin D Immunoglobulin E
Differentiated by the structural differences in the constant region of heavy chain
IgG
70-75%of total immunoglobulin
Secreted in high quantities
Cross the placenta
Has 4 subclasses
Functions of IgG
Neutralise microbes and toxins
Opsonise antigens for phagocytosis
Activate the complement
Protect the newborn
IgM
Secreted initially during primary infection
Cannot cross placenta
Largest antibody
Involved in agglutination and opsonisation
Large number of allogenic sites
Functions of IgM
Secreted first during primary exposure
Activates the complement
Used as marker for recent infection
IgA
Monomeric in serum, dimeric in mucosa
2 subtyPes
Major antibody found in mucosa
Dimeric with secretory component in the lumen of the gastro-intestinal tract and in respiratory teact
Major functions of IgA
Neutralises microbes and toxins
Activates complement
Helps minimise inflammation
IgD
Monomeric
Involved in production of sntibodies
Functions and applications of IgD
Present on surface oh B cells
Functions as membrane receptor
Has a role on antigen stimulated lymphocyte differentiation
Otherwise role unclear
IgE
Mediates type I hypersensitivity
Monomeric
Least quantifiable
Functions of IgE
Associated with anaphylaxis
Plays a role in immunity to helminthic parasites
B cell surface receptor
B cell activation
What happens in primary response
Following exposure to antigen, there is a slow rise in IgM followed by a slow rise in IgG
levels of IgM remain high transiently
What happens I’m secondary exposure
Following exposure to previously encountered antigen, there is a rapid rise in IgG and slow or no rise in IgM
Higher levels of IgG persist in small amounts throughout life
Plasma cell
Secrete antibodies
Survive a few days
Make 20p0 antibodies every second
Responsible for immediate defence
Memory cells
Live longer than plasma cells
Don’t produce antibodies directly
On contact with antigen, rapidly divide and develop into plasma and memory cells
What do B cells express when they reach maturity
Express both IgM and IgD
In what form does B cell produce antibody after activation
In secreted form rather than membrane-bound form
How does class switching take place
If activated B cell encounter specific signalling molecules via their CD40 and cytokine receptors, they undergo antibody class switching to produce IgG, IgA or IgE
What changes when class switching occurs
Constant region of antibody is changed
But variable region stays same
Since variable region is responsible for antigen specificity, antigen specificity is unaffected
Antibody retains affinity to same antigen
Only interacts with different effector molecules
How do antibodies protect us
Complement Neutralising extracellular pathogens Formation immune complexes Bind to lymphocytes Provides memory
