Introduction to B cells and Antibodies Flashcards
What is IgD?
Antigen receptor virgin B cells
What is IgM?
Agglutinin - activates complement
What is IgG?
Opsonin - activates complement
What is IgA?
Secretory - protects mucosa
What is IgE?
Protection vs helminths
List some Complements?
Cytolysis, Chemotaxis, Inflammation, Oposonisation
Where are B cells?
Stay in lymph tissue and respond to antigens by differentiating into plasma cells
How are B cells activated?
B cell receptors binding to specific antigents
What do B cells in lymph tissue respond to?
Unprocessed antigents or antigens presented
How do B cells secrete antibodie?
Once activated enlarge and differentiate into plasma cells
What are antibodies?
4 polypeptide chains, 2 identical heavy and 2 identical light
What are Heavy AA chains made up on?
450 AA
What are light chains made up of?
220 AA
How is light chain bound to a heavy chain?
By a disulphide bond
How are 2 heavy chains held together at mid-region?
2 disullphide bonds forms hinge region
What regions do both light and heavy chains posses?
V and C regions
Variable , constant
What is the Variable region?
Confer specificity of antibody, found at tips of H and I chains on antibody arms
What is Constant region?
Same in different antibodies and consist of H and L chains not associated with antigen binding
What does Binding of antigen binding site with antigen cause?
Neutralization, Agglutination, Precipitation
What is Neutralization?
Antibody covers bio active part of microbe
What is Agglutination?
Antibody cross links forming a clump
What is Precipitation?
Antibody cross links forming insoluble antigen antibody complex
Exposed FC portion following antigen binding promotes what?
Complement fixation, Opsonisation, Activation of NK cells
What is complement fixation?
FC of antibody complement protein activates
What is Opsonization?
FC region of antibody binds to receptors of phagocytic cells
What is activation of NK cells?
FC region binds to NK cells trigger TC chemical
What is a Complement?
Complex system of number of serum proteins act in a sequence in humoral defence against extracell microorgs
What are complement proteins?
C1-9
What are Complement factors?
D,B,Properdie
What are Complement receptors?
C1-3 - control proteins
What does Antibody bind to? IGM/IGG?
Epitopes of antigen
What does C1 bind to?
Fc region of antibodies
What does C1r activate?
C1s which is proteinase
What does C1s cleave?
C4
What does C4b bind to?
Antigen whilst C4a stays in fluid
What does C1 cleave?
C2
What does C2b bid to?
Antigen and c2a in fluid
What is C2b?
Proteinase cleaves C3
What does C3b bind to?
Antigen and c3a in fluid
What does c2b cleave?
C5
What happens to C5?
Doesnt bind, c5a in fluid
What does C5b bind?
C678 in fluid
What does C5b678 bind to?
Lipid bilayer
What does C9 do?
Inserts hole into membrane
What is microorg lysed by?
Membrane attack complex
Why are MACS deposited into bilayer of antigens?
Complement is enzymatic and cleave its substrate
What is an e.g of MAC?
E.coli
What does MAC do?
Form pores in lipid bilayer to kill gram negative bacteria
What happens to gram positive bacteria in MAC?
Protect themselves from complement mediated lysis by thick peptidoglycan wall
How do Funghi protect from MAC?
From complement mediated lysis by thick chitin cell walls
Where does Gram positive pathway end?
C5 cleavage
What are C3a and C5a?
Anaphylatoxins - activate mast cells
Chemotaxins - attract phagocytes
What is C3b?
Opsonin - enables phagocytes to recognise and bind to antigens
What is the alternative pathway?
Innate immunity with factors B,D,P activating enzymes
What is hyperacute rejection mediated by?
Naturally occuring antibodies to a-Gal
What is a-Gal?
Synthesised by a1,3Galactosyltransferase
What do humans express a-Gal as?
Foreign and it is an epitope and have high titres of antibodies in gut
Why are organs rejected?
Antibodies enter donor blood vessels and bind to a-Gal epitopes on endothelial cells, activating complement and neutrophils attracted, thromus blocks vessels, organ has no o2 and dies
What is hyper acute?
Preformed antibodies to Gal-a1 and Gal epitope
What is acute?
Direct pathway of immune recognition incompatible MHC II
Indirect pathway incompatible MHC I
What is the antibody titre?
measureof immunological memory
What is initial contact with antigen called?
Primary response
What is a second encounter with same antigen called?
Secondary response producing vast amount of IgG antibodies
Why does Age affect immunity?
Low levels of immune function, T cells less responsive to antigents
