ostuni 2 Flashcards
which type of immunity is mediated by B cells?
humeral immunity
which type of immunity is mediated by T cells?
cellular immunity
where are B and T cells produced?
B->bone marrow
T->thymus
How are B cell receptor and T cell receptors generated?
by somatic recombination.
the cells have to recombine their genome to generate their receptors
what are the two main players of adaptive immunity?
B lymphocytes (B cells)
T lymphocytes (T cells)
adaptive immunity is clonal, what does that mean?
each B cell and T cell has a unique receptor (generated by recombination of their own genome) that recognize a specific antigen.
innate immunity is non clonal, what does that mean?
each cell involved in the innate immune system express the same receptors
where is the variability of the B cell receptor?
in the variable region of the antibody. each B cell will have a different B cell receptor (a different antibody) with a different variable region.
the variable region is the region that recognizes the antigen.
what is the structure of an antibody? (B cell receptor)
-2 heavy chains connected to 2 light chains by disulfide bonds.
we have a variable region and a constant region
structure of T cell receptor
one alpha chain
one B chain
with one variable region (the antigen binding site varies between T cells)
combinatorial diversity to generate T and B cells receptors
the loci that encode for the T and B cells receptors are made of gene segments.
these gene segments are recombined to ensure that each B and T cell will have a different receptor able to recognize a different antigen.
RAG1 and RAG2
recombinase activating gene 1 and 2
specific recombinase enzymes for B and T cells that allow the combinatorial diversity to happen.
is non homologous end joining important to generate diverse TCR and BCR?
yes.
to recombine the different gene segments we need to apply double stranded breaks.
these brakes will be repaired by NHEJ that is imprecise and will contribute in adding diversity.
clonal deletion
-happens either in the bone marrow for B cells or in the thymus for T cells
-there is the deletion of the clones of both B and T cells that have generated a non functional or auto reactive receptor.
a non functional or auto reactive receptor can be generated because combinatorial diversity is extremely random and error prone.
what happens when a T/B cell with a functional and non reactive receptor recognize a specific antigen?
only that cell will start to proliferate.
we will have expansion of the appropriate clone
thymic involution
after puberty the cells that constitute the thymus begin to be replaced with adipose tissue and we progressively decrease the capability of producing new T cells.
The majority of the T cells that constitute our immune system are produced in the first years of life.
where does negative selection happen in the thymic lobe?
-in the medulla
-T cells with TCR that interact too strongly with antigen presenting thymic epithelial cells will give a death sign and will die (they are auto reactive). the others (that don’t interact too strongly with the thymic epithelial cells, non auto reactive) will survive.
where does positive selection takes place in the thymus?
-in the cortex
-a fully folded TCR will be able to transduce a survival sign and won’t die
what’s the name of the screening process that is happening in the thymus (including positive selection and negative selection)?
central tolerance
what is the name of the transcription factor that allows the thymic epithelial cells to mimic the expression of other tissues specific genes (and so tissue specific antigens)?
AIRE.
it prevents autoimmunity.
not only the cells auto reactive against thymic epithelial cells will be eliminated in the negative selection, but also the other ones auto reactive to other tissue-specific antigens.
what are the 2 main secondary lymphoid organs?
spleen
lymphonodes
the lymphonodes collect antigens from where?
from peripheral tissues by the lymphatics or actively transported by dendritic cells.
the spleen gets antigens from where?
from filtering the blood: the spleen gets the antigen that were circulating into the blood stream
where is the site in which the interaction probability between a T/B cell and its specific antigen is maximized?
secondary lymphoid organs
the cortex of lymphonodes is organized in 2 zones
B cells zone or outer cortex->enriched in B cells
T cells zone or inner cortex->enriched in T cells
where can we find the germinal center?
into secondary lymphoid follicles made by B cells in the outercortex of lymphonodes.
when B cells are activated and start proliferating, there is the developing of the germinal center (and so we go from primary to secondary lymphoid follicle)
what is the lymphoid component in the spleen?
the white pulp
which is a distributed tissue, a collection of follicles
where is blood being filtrated into the spleen?
in the red pulp
where are positioned T cells in the spleen? and B cells?
there is one central arteriole (where the blood flow) for each follicle made of B cells.
the T cells are organized right around the central arteriole.
