INTRO TO B CELLS AND ANTIBODIES Flashcards
what are B cells?
Stay in the lymphatic tissue and respond to antigens by differentiating into plasma cells
how are B cells activated?
by B cell receptors (BCRs) binding to specific antigens
what do B cells respond to?
to either unprocessed antigens or antigens presented by antigen presenting cells
initially respond to foreign antigens by taking in some of the antigen molecule, and then combining antigen fragments to MHC –II
what is the antigen-MHC-II complex recognised by?
by helper T cells which secrete cytotokines i.e. IL-2, IL-4, IL-6
what do cytokines do?
co-stimulate the B cells
what happens once B cells are activated?
some of the B cells enlarge and differentiate into plasma cells which secrete antibodies that are specific to the initial stimulating antigen.
Some become memory B cells.
what is the structure of an antibody?
consist of 4 polypeptide chains, two identical heavy chains and two identical light chains
what is the heavy chain made of?
of about 450 AA and also some additional carbohydrate chains
what is the light chain made of?
only consist of about 220 AA
how is the light chain bound o the heavy chain?
by a disulfide bond
how are the 2 heavy chains held together?
at the mid region by 2 disulphide bonds which forms the hinge region of the antibody
what forms beyond the hinge region on the heavy chains?
a common stem region
what 2 regions do both the light and heavy chain possess?
variable regions and the constant regions (V and C regions)
what is the V region?
confer the specificity of the antibody
where are the V region found?
at the tips of the H and l chains at the apex of the antibodies arms
how many binding sites does each antibody have?
2
what does the flexibility of the hinge region allow?
allows the 2 recognition sites to bind to quite widely separated antigens
what is the C region?
consists of those regions of the H and L chains not associated with antigen binding
does the C region of the heavy chain vary?
it does vary slightly between different classes of antibodies and this difference allows the classification of antibodies into 5 different classes., IgG, IgA, IgM, IgD, and IgE
what does binding of the antigen-binding site of an antibody with antigen cause?
neutralisation
agglutination
precipitation
what does the exposed Fc portion following antigen binding by the antibody promote?
complement fixation
opsonisation
activation of NK cells
what is a complement?
A complex system of a number of serum proteins which act in a sequence
what is the classical pathway of the antibody?
Antibody [IgM or IgG] binds to epitopes of antigen
what does C1 bind to?
C1 binds to Fc region of antibodies
what does C1r activate?
activates C1s which is a proteinase
what does C1s do?
cleaves C4
what does C4a and C4b bind to?
C4b antigen
C4a remains in fluid phase
what does C1s do?
cleaves C2
what does C2a and C2b do?
C2b binds to antigen; C2a remains in fluid phase
what does C2b bind to?
antigen
where does C2a remain?
in fluid phase
what is C2b?
a proteinase which cleaves C3
what do C3a and C3b do?
C3b binds to antigen; C3a remains in fluid phase
what does C2b do?
cleaves C5
