Final: Immune System Part 1 Flashcards
the immune consists cells that occur mainly within….
the circulatory system
collectively called white blood cells
innate immunity
cells part of a rapid response
adaptive immunity
cells part of a slow response
where are WBC formed?
in bone barrow
lymphocytes
B cells and T cells
brains of adaptive immunity
antigen
foreign molecules that evoke an immune response and are targeted by antibodies
antibody
proteins that can bind two identical antigens
mark antigens for destruction
found freely circulating in blood or mounted on B-cell surfaces
problem targeting antigens
how to locate and target them?
must be one antibody that binds the antigen before it can be destroyed
if the body doesn’t have the right antibody it can’t fight off the invader
what happens when an antibody binds an antigen
cross linking can occur forming antigen-antibody complexes
both binding sites of the antibody can interact with the same antigen
antigen labeled for destruction by macrophages
basic structure of an antibody
protein with two identical halves shaped in a Y
heavy chain and light chain protein
at the tip of each branch on top, there is an antigen binding site
variable regions
parts of the antibody that contact the antigen
different shapes like a pocket or groove
constant regions
parts below the variable regions
how is an antibody held together
disulfide bridges
hypervariable regions
part of the heavy and light chains where the actual antigen binding surfaces are
how is antibody diversity created?
antibodies are made by millions of b-cells
diversity comes from the variable regions
every b cell makes a single kind of antibody with a unique binding site
how many antibodies do b cells make?
~100 billion
essentially infinate
how many protein coding genes are in the human genome
20,000-25,000
keys to antibody diversity
alternative splicing
more importantly, gene rearrangement
antibody genes are put together from separate DNA regions
gene rearrangement
antibody genes are kits with alternative components
different kit for heavy and light chains
we inherit the pieces of each kit
heavy chain kit chromosome
14
light chain kit chromosomes
2, 22
parts of heavy chain proteins
V, D, J, C
parts of light chain proteins
V, J, C
what does VDJC stand for heavy chain
V: varible ~120 alternative variable regions
D: diversity ~27 alternative diversity regions
J: joining ~9 alternative joining regions
C: constant 5 alternative types of constant region
how many heavy chain genes do we have
~30,000
what does VJC stand for light chain
V: varible ~100 alternative variable regions
J: joining ~5 alternative joining regions
C: constant 2 alternative types of constant region
how many light chain genes do we have?
~ 500
heavy chain + light chain combination number
about 15 million combinations
far from 100 billion so how?
DNA splicing
sloppy splicing
VJ and VDJ splice-junctions are sloppy
bases are gained or lost b/c uses NHEJ
inserted nucleotides
in sloppy splicing a few more bases are inserted at junctions
this increases diversity of coding in spliced segments
sloppy splicing and inserted nucleotides make many…
frameshift mutations: make non-functional antibody genes
these b-cells just apoptose b/c nonfunctional
can you pass antibody genes onto children?
no, they are not in germline cells
new antibodies are expressed…
on the b-cell surface
how many antibodies does each b cell make?
just one
only uses one allele (allelic exclusion)
clonal deletion
young b cells die if they bind to an antigen
this is b/c whatever a young b cell binds to must be one of the body’s own molecules
clonal deletion prevents this young b cell from making an antibody that would attack the body
each b cells waits….
for an antigen that will bind its unique surface antibody
could live for 20 years or longer just waiting
b cells work with…
t cells
what happens when a mature b cell has an antigen bind its antibody?
the antigen is engulfed and cut into pieces
the pieces are displaced on the b cell surface
this may lead to activation of the b cell by a helper T cell
the activated b cell differentiates into plasma cells, which further manufacture the antibody
structure of a t cell receptor (TCR)
protein dimer has alpha and beta chain
each chain has a constant region and variable region
gene kits like antibodies
constant region attaches TCR to the
membrane
variable region of TCR
alpha-beta dimer forms single antigen binding site
t cells are derived from
arise in bone marrow
mature in the thymus
b cells are derived from
arise and mature in bone marrow
do t cells undergo a stage of somatic hypermutation?
no
are b cell receptors (antibodies) secreted in the blood and expressed on b cell membranes?
yes
are TCRs expressed on t cell membranes and secreted in the blood?
no, only expressed on the membrane
