Adaptive Immune System 1) Proteins Flashcards
What are antibodies also known as?
Immunoglobulins
What are antibodies produced by and where are they expressed?
by B lymphocytes
Expressed on surface of B cells
What are the main functions of antibodies?
- Prevent microbes entering or damaging cells
- Stimulate removal of microbes by phagocytes (opsonisation)
- Trigger destruction of microbes by stimulating other immune responses
How do antibodies prevent microbes entering or damaging cells?
Neutralise antigens
Agglutination of microbes
How do antibodies neutralise antigens?
By binding to that antigen
What are the given examples of toxins which antibodies neutralise?
Diptheria toxin (RNA Translational inhibitor) and tetanus toxin (blocks inhibitory neurotransmitter release causing muscle spasms)
What is agglutination of microbes?
The clumping together of microbes caused by antibodies binding on the surface of two adjacent microbes, preventing infection
What are large clumps of microbes and antibodies called?
immune complexes
What eliminate immune complexes?
phagocytes
How do antibodies stimulate removal of microbes by phagocytes?
opsonisation
Microbes are “tagged” by antibodies, enhancing phagocytosis
Which receptors expressed on the phagocytes surfaces recognise antibody tagging (opsonisation)?
Fc receptors
What other immune responses do antibodies trigger?
Complement activation
Natural Killer Cells
How do antibodies stimulate complement activation?
Antibodies bind to antigens, resulting in conformational change in antibody structure, exposing a binding site for C1q (the initiating factor of the classical complement pathway)
How do antibodies stimulate activation of natural killer cells?
Antibodies bind to antigens
Fc regions of bound antibodies are recognised by Fc receptors on surface of NK cells, activating NK cells and killing antibody coating cell
What is the structure of an antibody?
Large Y shaped globular glycoproteins, made of 4 polypeptides held together by disulphide bridges
What are the disulphide bridges like in antibodies?
2 identical heavy chain, 2 identical light chains, each containing a variable region and a constant domain
What are the 5 different antibody isotypes?
IgG, IgA, IgM, IgE, IgD
Which antibody type is most abundant in the blood?
IgG
Describe IgG.
Occurs as monomer, high addinity for antigen, actively transported across placenta
Which antibody provides antibody mediated immunity during foetal development and in neonates?
IgG
Which immunoglobullin is the second most abundant?
IgA
Describe IgA.
Occurs as monomer in blood and dimer in secretions. This dimer is actively transported across epithelial surfaces into secretions eg tears
What is the primary defence mechanism at mucosal surfaces such as bronchioles and nasal mucosa, and is the major secretory immunoglobulin?
dimeric IgA
Describe IgM
Large pentameric molecule, 5 IgM antibodies are joined together, contains many antigen binding sites
Where is IgM mainly found?
blood, but also expressed on B cells as a monomer
Which antibody is important in early stages of humoral immune responses?
IgM
Which antibodies are present at extremely low levels?
IgD and IgE
Describe IgD.
Expressed on surface of B cells
Describe IgE.
Produced in response to parasites
Involved in Type 1 Hypersensitvity (allergic) reactions by activating mast cells and basophils e.g. in asthma
Describe IgE’s involvement in allergy.
IgE is produced and binds to Fc receptors on mast cells. Antigen crosslinks and causes mast cell degranulation upon secondary challenge
Which antibody is responsible for neutralization?
Mainly IgG
Which antibody is responsible for agglutination?
IgM, IgG
Which antibody is responsible for opsonisation?
IgG
Which antibody is responsible for complement activation?
IgG, IgM
Which antibody is responsible forNK cell activation?
IgG
Which antibody is responsible for placental transfer?
IgG
Which antibody is responsible for neutralization at mucosal sites?
IgA
Which antibody is responsible for mast cell activation?
IgE
What is the Fab fragment involved in?
antigen binding
How many antigen binding sites are there per antibody molecule?
2 (IgM has many more binding sites)
What is the Fc region responsible for?
major biological actions of antibodies
Plays key role in activating phagocytes