3.1 Antibody Structure and Function Flashcards
What do B cells recognise?
Antigenic epitopes on the surface of pathogens
What is an antibody?
An antigen-binding protein
Soluble version of B cell surface antigen receptor
What secretes antibodies and where from/to?
Plasma cells in lymph nodes
Efferent lymph > blood > tissue (EXTRACELLULAR SPACE)
Where are soluble antibodies found?
Serum
Describe the structure of an antibody
Two heavy chains (protein domains) - constant regions
Two light chains - variable regions
Disulphide bridges and flexible hinge regions
Mirror image
What is the structural difference between a cell surface antibody and a soluble antibody?
Surface antibodies contain a transmembrane protein allowing it to attach to the cell surface, unlike soluble antibodies.
What are the three basic functions of antibody?
Neutralisation - prevents adhesion
Opsonisation - promotes phagocytosis
Complement activation - lyses bacteria
Describe neutralisation
Antibodies bind virus antigens to prevent them binding to cells
Describe opsonisation
Antibody coats pathogen to be phagocytosed by macrophage/neutrophil (Fc receptors)
Describe complement activation
Antibody binds antigen and intermediate molecule C1q allows antibody (adaptive) to link complement (innate) pathway
Leads to formation of Membrane-Attack Complex on surface of antigen
What determines the class/isotype of antibody?
Heavy chain gene determines class (Fc)
CH mu, delta, gamma, epsilon, alpha
What are the two types of light chain?
Light chain can be CL kappa or CL lambda
Random process and has little effect on biological function
How are the different heavy chains and light chains used to create the different classes/isotypes of immunoglobulins? (4)
- Lymph dev., recombination of light and heavy chains estalishes variable region
- B cell selects light chain constant gene (kappa/lambda) and leaves bone marrow
- Default is delta/mu (IgD/IgM)
- Activated by foreign antigen (in secondary lymphoid tissues) B cell can alter heavy chain gene to change class but keep same variable region and light chain (CLASS SWITCHING)
What is the function of IgD?
IgD(oorway)
- On surface of niave B cells
- Acts as membrane-bound antigen receptor
What s the function of IgM?
IgM (moneric or pentamic)
- Moneric IgM expressed as membrane bound antigen receptor on naive B cells
- Pentameric IgM - first antibody secreted in immune response
- Acts as agglutinin
- potent activator of compliment cascade