Immune System Part II Flashcards
what do antibodies do (3 steps)
- bind to and neutralize a bacterial toxin (also viruses and bacteria)
- coat the pathogen (opsonization) which promotes phagocytosis
- activate complement (IgG and IgM)
what is the ultimate goal of antibodies
target pathogens and their products for elimination by phagocytes
antibodies are:
the secreted form of the B cell receptor and are specific
what is the antibody structure
- 2 identical light chains
- 2 identical heavy chains
- each light chain is joined to a heavy chain by a disulfide bond (and noncovalent linkages)
- each light chain/heavy chain is joined to an identical light chain/heavy chain dimer by disulfide bonds
what do each light chain and each heavy chain contain
- each light chain contains one variable region and one constant region (of one domain)
- each heavy chain contains on variable region and one constant region (of 3 or 4 domains)
Fab fragment:
- fragment antigen binding
- composed of the light chain and part of the heavy chain
Fc fragment:
- fragment crystalizable
- a portion of the constant region of the heavy chain
what do Fc region of antibodies bind to
Fc receptors on cells, which aids in phagocytosis
epitope:
the portion of an antigenic molecule that is bound by an antibody
monoclonal:
one B cell and its clones will produce many antibody molecules, all of which will have the same specificity for their own epitope
polyclonal response:
there are likely to be multiple monoclonal antibodies generated to a particular antigen, all of the individual responses collectively are a polyclonal response
B cells all recognize the same ______ just different ____ on it
- antigen
- epitopes
complementary determining regions are also called:
hypervariable regions (contain 5 to 10 amino acids)
what forms the antigen binding site
the 6 hypervariable (3 on heavy and 3 on light) regions of heavy chain and light chain.
steps of generation of B cell antigen recognition diversity, and what do these steps ultimately lead to
- somatic recombination
- junctional diversity
- combinatorial diversity
- lead to billions of circulating B cells with unique specificity
what is somatic recombination
to generate the variable region in a light chain, one V and one J segment are joined. to generate the variable region in a heavy chain, one V, one D, and one J segment are joined. There are multiple V, D, J segments to randomly choose
what is junctional diversity
addition of new and random nucleotides at the V and J segments of light chain and D and J segments of heavy chain
what is combinatorial diversity
different light chains combine the already generated heavy chain
what are B cells expressing when they leave the bone marrow
IgM
what happens before B cells leave the bone marrow
they undergo a selection process so that they do not have a strong recognition of self
what happens to B cells that do not encounter an antigen
they undergo apoptosis
in the bone marrow, in a b cell -
heavy chain is generated first: somatic recombination, junctional diversity, addition of µ constant region. Same heavy chain, but different light chains
what are the 5 classes of antibodies
IgG, IgM, IgD, IgA, IgE
the first class of antibodies produced during an infection are:
IgM class antibodies
when and where does class switching take place
in lymph nodes following B cell activation and with help from T cells
what happens when B cells leave the bone marrow
- they circulate between blood and lymph
- if they encounter an antigen, they phagocytose that antigen and are considered activated
- in order to secrete antibody they need T cell help, which takes place in the lymph node
- a B cell will phagocytose the antigen and present pieces of it to a T helper cell in the context of an MHC molecule
what is the germinal centre and what doesn’t have one
a specialized microstructure that forms in secondary lymphoid tissues. IgM secreting B cells do not have a germinal centre
B cells that enter the germinal centre of a lymph node:
undergo somatic hypermutation, with the purpose of generating antibodies of higher affinity for the antigen
affininty maturation:
B cells that display higher affinity
what happens to B cells that have affinity maturation:
they are selected for and undergo class switching (isotype switching) with the aid of a T helper cell
what happens to the B cells that undergo class switching
some will become plasma cells, some will become memory cells
what happens to B cells that do not display higher affinity or no longer recognize antigens at all
apoptosis
plasma cells have one job:
to secrete antibodies
T cells originate in the ______ and mature in the ______
- bone marrow
- thymus
T cells enter the thymus as:
double negative cells: do not express CD4 or CD8
as T cells proliferate:
they rearrange their T cell receptors. T cells recognize self-antigen are eliminated during this process. T cells that leave the thymus are either CD8 and CD4
to become activated, T cells:
must recognize antigen, not directly as B cells do since T cells only recognize antigen presented on the surface of MHC molecules
MHC Class I are recognized by:
MHC Class II are recognized by:
- CD8+ cytotoxic T cell receptors
- CD4+ helper T cell receptors
T cells are activated by:
dendritic cells
dendritic cells carry:
antigens from sites of infection to secondary lymphoid tissue where they become active and present antigen T cells
