Primary and secondary lymphoid organs Flashcards
where does Sequential rearrnagement of antigne receprot genes take place?
BM ( B cells) or thymus (T cells)
Describe the development of B cells in the bone marrow
- rearrnagement of heavy and heavy chaisn to get functioanl BCR membrna ebound IgM or igD
- leaves the BM are mature but naiev B cells
- mature B cells leave the bone marrow
- migrate to secondary lymphoid tissues (spleen lymnodes)
- to mature further- vai T cell dependent or idnependnet way
what is the role of bone marro stromal cells
provide sutibale microenviroment for B ceel developmetn
without cannot have functional gene rearrrangemtn for BCR
release cytoine IL-7- esswntial.
describe a otherview of T cell development?
HSc—> T cell lineage in BM
migrate to thymus
Development of TCR( functioanl geen rearrangment)
+/- selection
Describe the Thymus
multi lobed organ
outer capsule- fiborus protection
2 distincit inner layersouter cortex, inner medulla (each ahs role in T cell maturation
Hassalls corpuscle
what happens to the thymus with age?
sequesters with age- T cell response diminished- may lead to increase infections in elderly
where are Hassalis corpuscle found and what can we use them to identify/ purpose
found in the thymus Medulla
idnetify thumus in histology
instruct dendritic cells to induce Cd4+ CD25+ regualtory T cells in human. Potent source of TSLP
what is this the Histology of?
The thymus
Describe T cell development in adult
Progenitor T cell form BM
double negativ ethrymocytes (CD4-,CD- also TCR-)
T cell preucors enters subcapsular cortical areas
encounter netowrk of cortical eptihelail celsls (thymic stroam IL-7 again)
cortex- double negative cells, functional rearranagement of A and B TCr chains- then express Cd4 or Cd8. then negative selection
Medulla- positive selection, become single positive (cd4 or Cd8)
what happens to the thymus output with age?
sequesters with age
less robust reposne to novel infections- fall in thymic ouput
number of memory T cells maintained
number of new naive T cells we produce decreases over time
increase in ifnections with age, dififuclty with new infections
describe the Secondayr lymphoid organs
main sites of immune acitvation against anrtigen ( T cell dependent)
spleen also importnatn in B cell developement
follicular B cells
MZ B cells
what is the function/structure of lymph nodes
main drianage/filter for lymoph for antigens from peripheral tissues ( free soluble antigens and on AP follcilualr denritic cells)
highly vacualrised
in tact with lymph and blood supply
have follicles which may contain germianl centres
(MZ = mantle zone, possibel population of T cells and unactivate dB cells), Germinal centres= B cells
what is this histology of
GC- germinal centre B cells, within a follicle
MZ- T cells
in the lymph node where are B and T cells mainly found?
B cell- in the follciles
T cells in the paracortex
in the Lymph node paracortex- whare are the high endothelial venules purpose? (HEV)
Allow T cells to enter directly from the blood into the lymph node paracortex ( also enter via a fferent lymphatic vessels)
can be recognsied by cuboaidal epithelials clles
in T cell dominant immunological response may obsevre expansion of the paracortical region
what is the function of the Spleen?
filtration fo blood
main protection agaisnt blood borne pathogens (lymph nodes for tosses)
cotnain follicles populated with fB cells (B cells- T cell depnent acitvation)
follicles have mrginal zone- MZ Bcells ( t cell indepenedt
Describe the structure of the spleen
high;y vasuclarised organ
encapsulated
red pulp (70%)- reserovir of RBC, platelts macorphages
white pulp- mainyl lymchoytes (T and B cells)
seperated from Red pulp by a marginal zone- this traps parituclate matter and presents to lympgocytes in white matter
describe the histology of the spleen?
red and whit epulp mixed together
Trabecula- conective tissue around the spleen - supprots spleen and carries blood vessles
describe the white pulp of the spleen
Germinal centre surroduned by a marginal zone then a mantel zone
(marginal zone - b cells ( t cell independent)
what type of lymphocytes might you see in the periarteriolar lymphoid sheath
T cell rich zone
where do the lymph nodes and spleen individually pick up infections
Lymph nodes- peripheral tissiues
spllen- in the blood
what is this the hisotlogy of?
tonsils- Malt tissues
Muscoal associated lymhpoid tissues
encpasulated
two palatine, 1 lingual, 2 tubula 1 adneoid
what are payers pathces
example of diffuse malt/ GALT
commonly found in the ileum
lies right beneatht the mucosal layer
cotnain M cells- specialsiezed eptihelial cells that reside abov peyers patches to take up antigens (have germianl centres)
what is the role of Germianl centres with T cell-dependent memroy B cell generation
antigen acitvated B cells and T cells by dendiritc cell migrate towards the border of thje B cell follcile and the T cell zone of secondary lympgoid organs
esrtbalish stbale Bcewll- T cell interations. Enables B cell to reicve signals for cognate Cd4 + cells
once acitvate B and T cells move to the border of the outer follicle
- B cell undergo dproliferation some into palsam cells otheer into Memory cells and remain in the fermianl centre
what is the dark zone of the germianl centre?
