Lymphocytes Flashcards
place of B cell development
gestational phase -> embryo and foetal liver
after birth -> only bone marrow
2 phases of B cell development
maturation (within the bone marrow) and differentiation (outside the bone marrow)
where are memory B cells stored
mostly secondary lymph nodes
what process is happenning during B cell development in the bone marrow
selection process - B cells need to be self tolerant
in what state do B cells exit the bone marrow
as immature B cells - once they enter circulation = naive B cells
what does it mean if a B cell is naive
the B cell has not encountered a foreing antigen yet
what phase of B cell development is antigen-dependent
the differentiation - antigen-activated maturation of naive B cells to antibody-secreting plasma cells and memory B cells
describe B cell phases during development (considering gene rearrangement)
lymphoid stem cell (DhJh recombination) -> pro-B cell (VhDhJh) -> pre-B cell (VlJl) -> immature B cell -> naive B cell -> mature B cell
where does T cell development take place
starts in the bone marrow - immature / progenitor T cells travel to the thymus -> completion of differentiation
where do T cells undergo somatic recombination and what is the purpose of this process?
thymus and it is useful for the generation of T cell clones with unique receptors
what is a double negative T cell
a progenitor T cell which is not expressing either CD4 or CD8
briefly describe T cells development stages
(bone marrow) HSC -> TSP -> (thymic cortex) DN1 -> DN2 -> (subcapsular zone) DN3 - now the cells can differentiate into gamma-delta T cells -> DN4 -> now they start expressing both CD4 and CD8 = DP cells (cortex again - pos selection) -> SP (medulla - neg selection)
what is the other name for T cell progenitors
thymic seeding progenitors
briefly describe T cell pos selection
junction of cortex and medulla is lined up with epithalial cells which expresses MHC I and II molecules -> DP T cells bind to one of the MHC molecules which determines if the become CD8 or CD4 T cells (if they are unable to bind they undergo apoptosis)
what kinase is essential in the positive selection of T cells?
the Lck tyrosine kinase is recruited to the TCR which initiates signalling -> leading to T cell maturation
what is negative selection of T cells?
if the T cells bind to stringly to self-MHC molecules they undergo apoptosis
clonal selection theory
lymphocyte receptors are produced in billions of different versions (each capable of binding a different ligand) -> once there is an antigen presented by an APC and there is a T cell / B cell that recognizes this antigen –> proliferation and differentiation of activated specific lymphocytes to form a clone of effector cells (so creating a million copies of the same lymphocyte to fight the infection)
afferent lymphatic vessels
connects tissues to secondary lymphoid organs
efferent lymphatic vessels
connect secondary lymphoid organs to tissues
what are high endothelial venules (HEVs) and their function
special venules inside the lymph nodes which allow naive B and T cells to enter the lymph node –> they come from the blood circulation
where do B cells reside within a lymph node
in the lymph node follicle
what is a germinal centre
a microstructure that forms in secondary lymph nodes -> that is were activated B cells migrate and were they differentiate into plasma cells + proliferate
what is the function of the spleen
screens for pathogens in blood
what is the differnce between the spleen and lymph nodes?
the spleen has a central arteriole which is constantly sampled for blood pathogens. a lymph node is “supplied” with pathogenic antigens by APCs which deliver them through the aferent lymphatic vessel
what is GALT
gut-associated lymphoid tissue
what are M cells, where are they located, what is their function?
microfold cells, located in the epithelial lining of the lumen, and their role is to constantly uptake antigens from gut lumen
how are antigens from the gut lumen delivered to DCs in GALT
via transcytosis performed by M cells
