Humoral Immunity Flashcards
what receptors are expressed on naive B cells
IgD and IgM
what proteins help transmit signals from the BCR complex
Igalpha and Igbeta
CD21
b-cell marker what receives co stimulatory signals from complement
where are B and T cells distributed in the lymph node?
b- follicles, t- paracortical regions
What happens when a t-dependent antigen gets presented to a b cell
proliferation and upregulatoin of CD80. it down regulates CXCR5 and upregulates CCR7, which moves it to the paracortical region. it takes in the Ag and processes it into a MHC class 2 complex for presentation to a CD4 T cell.
what is the importance of CD40L
this is expressed on t cells and activates b cells during t-dependent humoral responses. It strengthens the b cells response to the antigen and sends it back to the germinal center, where it will proliferate and differentiate into plasma and memory b cells
what is the difference between a plasma cell and a memory b cell?
plasma cells are shortlived and generate antibodies. memory cells live in the bone marrow and are ready to proliferate into plasma cells in the case of a second exposure
what is the difference between a primary and secondary response?
primary responses take about a week. Serum IgM appears first, followed by G and A.
secondary responses are much faster b/c of existing memory cells from a first exposure. the primary ab class will be IgG and it will have a higher affinity for the Ag than previously
serum memory/clonal selection
older, lower affinity plasma and memory cells are replaced by newer, higher affinity cells in the bone marrow
describe class switching
upon CD40 ligation, Abs can switch isotypes in the germinal center. this occurs b/c the VDJ sequence gets translocated downstream of the IgM C region. where the VDJ region moves to is regulated by the cytokines present. when it is done moving, the intervening DNA is cut out, leaving a new mRNA transcript but the same specificity
TGF-B is associated with class switching to which type?
IgA
affinity maturation
occurs in germinal centers where B cells proliferate and somatic mutations are occuring. slight mutations change the affinity for the Ag, and it gets bound increasingly as proliferation continues. thus, only high affinity mutations will be able to out compete a limited supply of Ag, and competitors will die off, leaving only highly specific Abs.
describe t-indpendent activation
non-peptide Ags. usually bind with tighter affinity to epitodes and activate multiple BCRs b/c of repeating epitopes, so the b-cell can still mount a response
usually see a IgM response peaking earlier than T-D responses, however no class switching is seen w/o t help. affinity maturation and memory b cell formation isnt seen
describe the status of the immune system in newborns
they have more mature T or B cells than adults, but their immune systems are very immature and cannot yet mount responses. reasons for this include:
sequential expression of genes for Ag specific receptors
immaturity of B and helpter T cells
APC immaturation
describe passive immunity in the newborn
newborn cells have IgM only, so they receive IgG across the placenta from mom, and slowly start making their own after birth
IgA only begins getting made after 1-2 months, and IgA from breast feeding is used until that point
