immune response in peripheral lymphoid organs Flashcards
What happens to the B + T lympcytes after they mature and become immunocompetent in central Lymph organs
move to the peripheral or secondary lymphoid organs.
There, immune response is mounted and
carried out.
what is antigen dependant differentiation
Lymphocytes meet antigen and are
activated by it. They proliferate to clones
and differentiate to effector and memory
cells.
examples of peripheral lymphoid organs
lymph nodes, spleen, + mucosa-
associated lymphoid tissue (MALT).
what do lymph nodes do + why they swell with infection
Antigens penetrating tissues (esp.
after injury) will be drained by lymph and brought
to the nearest lymph node to be dealt with.
Structure of lymph node
covered in capsule of conn tissue
- cortex - mostly a B-cell area. It contains cell
aggregates called follicles. - paracortex - a T-cell area. There, T
lymphocytes proliferate in cellular immune
response. - medulla - rich in antibody-secreting plasma
cells.
what are the follicles called if they are engaged in immune response and when they engaged in humoral response
- primary (small and dense)
2.secondary (enlarges + middle
forms area called germinal center. This is site of proliferation + antigen-dependent differentiation of B lymphocytes.)
What are HEV in lymph nodes
High Endothelial Venules
specialized blood vessels that deliver naïve lymphocytes from the bloodstream into the lymph nodes, where lymphocytes become matured by antigen-presenting cells
(e.g., dendritic cells).
how do lymphocytes exit into blood
through efferent lymph vessels and into thoracic duct
Steps of B cell differentiation in follicle
- Antigen recognition at
the periphery of follicle. - Stimulation by Тh (at the periphery).
- If B cells stay at PERIPHERY, they do not
undergo class switch and
hypermutations; differentiated into SHORT- lived plasms cells.
4 B clells that enter GERMINATIVE CENTER of follicle undergoes class switch + somatic hypermutations. differentiated into LONG lived plasma + memory cells
what does spleen do
reacts against blood borne antigens
structure of the spleen
RED pulp - formed by cords + vascular sinuses. function = blood storage
WHITE pulp - is lymphoid organ. concentrated around arterioles
page 9 for image of spleen. what is the periarteriolar. what is marginal zone
- lymphoid tissue closest to the arteriole (t cell area)
- peripheral white pulp bodering red (B cell area)
What does Musosa assoc lymphoid tissue (MALT) do
reacts against antigens encountered at mucosal surfaces of respiratory, gastro-intestinal and genito-urinary tract.
why is MALT also called non encapsulated lymphoid tissue. examle organs
its organs lack conn tissue capsules
tonsils, adenoids, peyers patches + appendix
what kind of Ig does mucosa assoc humoral immunity rely on comapered to humoral immune response
IgA
humoral response = IgG
what are MALT subcompartments
nasopharynx-associated lymphoid tissue,
bronchus-associated lymphoid tissue
gut-associated lymphoid tissue
genital tract-associated lymphoid tissue.
does immune response occur in mammary glands
NO
but IgA antibodies are secreted to combat antigens in nasopharynx + gut
Phases in immune response
- Antigen presentation + recognition.
- Lymphocyte activation.
- Lymphocyte proliferation (clonal expansion) and antigen-specific differentiation.
- Antigen elimination (effector phase).
- Contraction of the immune response.
- Memory.
what a is the effector phase
- elimination of antigen mediated by specific antibodies
and T cells. carried out i peripheral lymph organs
-
how are effectors made
interction btw T + B lymphocytes and antigen presenting cells
- they interact by contact dependant and parcrine signalling (cytokines)
what are t lymphocytes that haven’t participated in immune response called
naive , virgin, unprimed. in resting state
how is a naive t cell activated
TCR needs to be engaged
co stimulatory signal needed ( delivered by membrane protein B7)
what do dendritic cells express and where they found
MHC both classes+ B7
found under skin + mucosa (pathogens invade here)
in skin they called Langerhans cells)
how does the dentritic cells activate t cells
After phagocytosing a particle, the dendritic cell migrates to nearest lymphoid organ to present its digested antigens.
There, it activates T cells, even if they are naïve.
requiments for t helper cell activation
contact with MHCII + peptide and B7
how are T killers activated
antigen presentation of MHC I + B7 AND TH1 helper recognizing same antigen
- T killers and T helpers specific for the same antigen stay close but cant recognise eachother
- they meet on the surface of antigen-presenting cell.
- The activation signal from the T helper is a cytokine, most likely interleukin 2
How do dendritic cells present peptides both by MHC-I and MHC-II (antigen cross presentation)
After phagocytosis in dendritic
cell, pathogen is processed
in lysosomes + presented by
MHC-II to be detected by T helper.
Some protein molecules of the same pathogen can be
transferred to proteasomes;
these will be presented by MHC-I
to be detected by Tc.
This allows DC to contact both
Th and Tc and to keep them
close to each other.
what else can antigen cross presentation allow dendtritic cells do
present viral antigens without being
infected by the virus.
Once activated, T cells start to divide, forming
clones. what happens after this
proliferation by interlukin 2.
they become effector cells
when activated t cell recognises antigen with appropriate MHC, its triggered to act
Is there a need for co simulatory signals for activated t cells.
No doesnt need B7 or interleukin 1 to kill
so how does activated TC kill
they activate T killers + macrophages, and activated Th2 cells activate B cells.
Activated T killers and Th1 helpers do not stay only
in lymphoid organs but disseminate to other organs
by circulation.
B cells only hv IgM receptors (as from bone M) for immune response they need IgD too. where do they get
obtain it from the same genes by alternative RNA processing and coexpress IgM and IgD.
activation of B cells
- do not need antigen presentation as T cells do. (can present antigen alone so acts like Ag presenting cell)
- Thymus independent antigens causes B cells recognising them to proliferate and differentiate to secrete IgM antibodies
what is specific abt germline centre B cells
high affinity, class switched antibodies
requires somatic hypermutation to dvlp
they origin of best memory B cells
whats specific abt short lived antibodies
quickly forms in secondary lymph organs but apoptosis few days after antibody secretion.
some survive and become part of long term humoral immunity
Most antigens are T-dependent and cannot
activate naïve B cells by themselves. They
need a T helper of Th2 type.
how do these recognise eachtoher
- B cells internalize antigen bound to their
receptors, process it + present it with class
II MHC. - allows B cells to be recognised by T helpers specific for same antigen
- T helper induces B cell to proliferate a + differentiate by cytokines
Unlike IgD whch uses alternative splicing, how can B cell produce IGg, IgA, Igd?
site specific recombinsation
similar to VDJ
