0506 - B cells and antibodies - EG Flashcards
What are antibodies?
immunoglobulin proteins secreted by activated B cells (plasma cells), the same unique protein is also present on the B cell surface (each B cell has a unique protein)
Define affinity.
The binding strength between the antibody and antigen at a single binding site.
Define avidity.
The binding strength of an antibody and antigen at a number of binding sites.
Describe the structure of an antibody.
Two chains, a heavy chain and a light chain. both have a variable, V, and constant, C, region, however the C region of the heavy chain is longer so as to either create a tail in free antigens or to embed in the plasma membrane on the surface of B cells. The variable region determines antibody specificity.
What is found within the variable region?
complementarity determining regions (CDRs) that determine specificity of the antibody to an antigen.
What is the function of IgG?
opsonisation of antigens for phagocytosis by macrophages and neutrophils, activation of classical pathway of complement.
What is the function of IgM?
Activation of the classical pathway of complement, but more niave antigen receptors.
What is the function of IgA?
Mucosal immunity, found in lumens of GI and respiratory. activation of complement by the lectin or by alternative pathway.
What is the function of IgE?
mast cell degranulation
Which immunoglobulin type activates the classical pathway of complement?
IgG and IgM.
Which immunoglobulin type activates the lectin or alternative pathway of complement?
IgA
Which immunoglobulin type forms a pentamer?
IgM
Which immunoglobulin type forms a dimer?
IgA
Which immuloglobulin types predominate in serum?
IgG and IgM
What is somatic hypermutation?
The process by which germinal centre B cells mutate their B cell receptor to increase its affinity to an antigen by random mutations, the advantageous of which are known as affinity maturation.
