lec 15- the immune response part 2 Flashcards
(58 cards)
what do antibodies do?
- bind to and neutralize a bacterial toxin
- coat the pathogen which promotes phagocytosis
- activate complement
overall: target pathogens and eliminate them via phagocytosis
what is the secreted form of B-cell receptors?
antibodies
what is the structure of an antibody?
-2 identical light chains
-2 identical heavy chains
-each light chain is joined to a heavy chain by a disulfide bond
- both light and heavy chains consist of one variable and one constant region (light have one domain, heavy has 3 or 4)
what is the Fab fragment?
-fragment antigen binding
-composed of the light chain and part of the heavy chain
what is the Fc fragment?
-fragment crystalizable
-a portion of the constant region of the heavy chain
what do the Fab and Fc fragments bind to?
Fab binds to the antigen and Fc binds to Fc receptors on cells
what is an epitope?
the portion of an antigenic molecule that is bound by an antibody
can an antigen have multiple epitopes?
yes,
what does a B-cell do when it recognizes its antigen?
it will multiply and produce clones of itself, all of which will secrete antibodies
do B-cells tend to recognize inner epitopes?
no, they recognize external epitopes
what are the hypervariable regions of an antibody also known as?
complementary-determining regions (CDRs)
what do the 6 hypervariable regions of heavy and light chains form?
antigen binding sites
what are the three steps of the generation of B cell antigen recognition diversity?
- somatic recombination
- junctional diversity
- combinatorial diversity
what is somatic recombination?
-to generate variable region of light chains, V and J segments are joined
-to generate variable region of heavy chains, one V, D, and J segments are joined
- V, D, and J segments are randomly chosen from many
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 do the randomly chosen V gene segments code?
they code CDR1 and CDR2
what does junctional diversity code?
CDR3
what is combinatorial diversity?
-B cells with intact heavy chains undergo clonal expansion, light chain generation then takes place (same heavy chains but light chains can be different)
-different light chains combine the already generated heavy chains
-before B cells leave bone marrow, they undergo a selection so they dont recognize themselves
-three steps that lead to the creation of circulating B cells with unique specificity
A clone of mature B cells released from bone marrow have:
one antigen specificity and express lgM receptors, meaning first class of antibodies are lgM class antibodies
what happens when B cells leave the bone marrow?
-they circulate between blood and lymph, need antigen to be activated
-need help of T cells to secrete antibodies
-takes place in lymph node
-B cells will phagocytose the antigen and preset pieces of it to helper T cells
what are class I MHC molecules?
molecules that are expressed on all nucleated cells, generally present viruses to cytotoxic T cells (CD8) which kills infected cell
what are class II MHC molecules?
molecules that are expressed on professional antigen presenting cells, present extracellular pathogens that must be phagocytosed before presentation
what is the structural difference between class I and II MHC molecules?
class I: one transmembrane alpha chain of three domains that are non-covalently complexed to B2 microglobulin
class II: two transmembrane chains- alpha and beta
what ends up in the binding sites of class I and class II MHC molecules?
pieces of antigens
