Humoral Immunity Flashcards
What is humoral immunity?
Immunity provided by antibodies that are present in bodily fluid
Humoral immunity refers to immunity mediated by?
B cells
What is meant by T dependent antigen?
The B cell response to most antigens requires assistance from helper T cells (Th)
What is meant by T independent antigen?
T independent antigen elicits antibody production by B cells without T cell involvement
If an individual has an immune response to an antigen characterized by production of IgM but no IgG or IgA, what could you infer about the antigen?
The antigen is T independent
What does class switching require?
CD40L on the surface of a T cell
What can B cells act as professional antigen presenting cells for?
Antigen experience T cells
Describe the structure of antibody
Consists of 2 identical heavy chains and 2 identical light chains. The two heavy chains are linked to each other by a disulfide bond. Each light chain has a disulfide bond linking it to one of the heavy chains. The entire structure weights about 150kDa.
Describe the divisions of the antibody
2 parts: variable and constant
Variable: antigen binding
Constant: effector functions
What else can the antibody be divided into?
Fab: Fragment antigen binding-there are 2 fabs
Fc: Fragment crystallisable-the constant region of the heavy chains
What determines the isotypes/different classes of antibodies?
The heavy chain constant region
Where is the “hinge” located?
Between the CH1 domain and the CH2 domain
What are the hypervariable regions called, and why? (CDR1. CDR2, CDR3)
Complementarity Determining Regions
The amino acids within the CDRs are complementary to the amino acids in the antigen that is going to be recognized
Which two classes of antibodies can polymerize or form polymers?
IgA and IgM
Which antibodies are found in monomeric form?
IgA, IgD, IgE
Cell surface IgM
Circulating IgA
Which antibodies are found in dimeric form?
Secretory IgA
Which antibodies are found in pentameric form?
Circulating IgM
What is the J chain?
A protein that joins together individual units of antibodies when they polymerize
Which is the most dominant class of antibody in circulation?
IgG at 620-1400 mg/dL
What are epitopes?
The area on the antigen that is recognized by the antibody. The larger the antigen, the more epitopes present.
Why is the binding of an antibody to an antigen a reversible process?
All of the bonds involved are non covalent. Covalent bonds such as the disulfide bond between the chains of the antibody are irreversible.
Amino acids in the Complementarity Determining Region interact with amino acids in the epitope using non covalent reversible forces. What are the four major forces involved?
- Hydrogen binding
- Electrostatic interactions
- Van der Waals interactions
- Hydrophobic interactions
Overall binding strength=affinity
What is functional affinity?
The
What can antibodies, acting on their own do, when not acting as a bridge between the antigen and other components of the immune system ?
Neutralize bacterial toxins
Block viruses binding to cellular receptors
Block adherence of bacteria to mucosal surfaces
Name ways in which antibodies act as a bridge.
- clearance of immune complexes by RBC (IgM, IgG )
- opsonization for phagocytes (IgG)
- antibody dependent cellular cytotoxicity (ADCD) (IgG)
- generation of membrane attack complex (IgM, IgG)
- mast cell degeneration (IgE)
Give the functions of the IgM and IgG class
IgM: first class produced in adaptive response, activates complement, powerful agglutinin.BCR on B cells, secreted IgM mainly in circulation-pentamer with J chain. Can’t cross placenta
IgG: main antibody in 2nd response to antigen, most abundant in circulation, activates complement, opsonizes bacteria and beatralizes bacterial toxins and viruses. Only isotope that crosses placenta
Give the functions of the IgA class
Secretory form prevents colonization at mucosal surfaces. Produced in GI tract and protects against gut infections.
Give the functions of the IgD class
BCR (with IgM) on naive B cells. Found on surface of many B cells and in serum
Give the functions of the IgE class
In presence of antigen, triggers release of inflammatory mediators from mast cells and basophils. Contributes to immunity to parasites by activating eosinophils. Lowest concentration in serum.
