515 immuno - lymphoid organs + tissues

lymphoid tissues

tissues in which lymphocytes are found

diffuse lymphocytes

1st stage of lymphoid tissue range in organization

lymphoid follicles

clusters of lymphocytes

lymphoid patches

groups of lymphoid follicles

encapsulated organs

groups of lymphoid follicles that are encapsulated by specialized-supporting tissues/membranes

primary + secondary

two categories of lymphoid tissues based on their function and anatomy in humans

bone marrow + thymus

primary lymphoid tissues

lymph nodes, spleen, MALT + SALT

secondary lymphoid tissues

maturity + central tolerance

what do lymphocytes learn in primary lymphoid tissues?

hematopoiesis

bone marrow is the primary site of _______ in the adult human

stromal cells + adipocytes

the remainder is non hematopoietic cells in the bone marrow

stromal + hematopoietic

types of IMPORTANT cells that the bone marrow is tightly packed with

spongelike, reticular

framework of bone marrow

blood-filled sinusoids

spaces within the bone marrow

central cavity

outer matrix of the bone marrow surrounds a _______

honeycomb

structure of the central cavity

trabeculae

thin strands of connective tissue within the central cavity

red, yellow

types of marrow within the trabeculae

red

type of marrow that is haematopoietically active and contain vast numbers of erythrocytes

yellow

marrow that is not active and is full of adipocytes

stromal cells

cells that are not hematopoietic but push immune cell differentiation

long-lived plasma + memory cells

bone marrow is not only a site for myeloid and lymphoid development but is also a site to which fully mature myeloid and lymphoid cells can return

stem cell niche

Within each trabecular cavity, the network of stromal cells and blood vessels form a framework supporting HSCs known by the

stem cell niches

this is what contains osteoblasts, endothelial + reticular cells, sympathetic neurons

osteoblasts

cells that both generate bone and control the differentiation of HSCs

Endothelial cells

line the blood vessels and regulate HSC differentiation

Reticular cells

send processes connecting cells to bone and blood vessels

Sympathetic neurons

control the release of hematopoietic cells from the bone marrow

endosteal + vascular niche

there are two zones in each trabecular cavity

endosteal niche

zone in trabecular cavity that is occupied by quiescent/undifferentiated HSCs + osteoblasts that regulate stem cell proliferation

vascular niche

zone in trabecular cavity that is occupied by differentiated HSCs and is lined w/ blood vessels

happen at the same time

migration and differentiation either happen do/don’t happen at the same time when HSCs move from endosteal to vascular niche

outer

where is the endosteal niche in the bone marrow?

center

where is the vascular niche in the bone marrow?

thymus

site of T cells maturation

Jacques Miller

Australian biologist, worked against the power of popular assumptions and proved that the thymus is an important cite for maturation of T lymphocytes

lymphocytes

thymectomised mice were missing ______ in their circulating blood cells

blood

hematopoiesis in the bone marrow generates lymphoid precursors that travel via the ____ from the bone marrow to seed the thymus

chemokines

epithelial cells of the thymus secrete ________ that specifically attract these precursors from the blood to the thymus

no

when immature T cells within the thymus pass through defined developmental stages, they mature naive T cells. however, do they have properties as an effector. yes or no?

bi-lobed

the characterized structur of the thymus

encapsulated + multilobed

within each lobe (bi-lobed), what is their nature?

cTECs + mTECs, DCs + macrophages

the process of developing thymocytes interact with and supported by these cells within the thymus

thymic involution

After puberty, the thymus starts to regress with replacement by adipose tissue (AdT), thus the thymic production of mature T cells greatly decreases; inflammaging

increase mature T cell production

how to counter thymic involution?

thymic cortex

where to find cTECs?

thymic medulla

where to find mTECs?

central tolerance

thymus is a specialized environment where immature T cells generate unique antigen specific receptors (TCRs) and are then selected based on their reactivity to self antigens expressed on the surface of thymic stromal cells

negative selection

thymocytes whose TCRs bind self antigens with high affinity are induced to die

positive selection

those thymocytes that bind self antigens with low affinity are the only that survive

blood + immune system

immune cells are the most mobile cells in a body and use two different systems to traffic through tissues

lymphatic system

network of thin-walled vessel that play a major role in immune cell trafficking, between tissues and lymph nodes

lymph

protein-rich fluid

plasma

fluid component of blood

intersitial

type of fluid that contains lymph, which is derived from plasma, and seeps through the walls of capillaries into surrounding tissues

single porous

walls of the lymphatic vessels consist of a _______ layer of endothelial cells

blood

All cells and fluid circulating in the lymph are ultimately returned to

thoracic duct

largest lymphatic vessel

right arm + side of head

thoracic duct collects lymph from all the body, except:

right lymphatic duct

where does lymph from right arm + side of head go into

one-way

flow of lymph is achieved by the movements of the surrounding muscles and a series of _________ valves

invasion + capture

stage of the lymphatic system wherein foreign antigen enters tissues and is actively picked up by the lympathic drainage network

transport + enrichment

stage of the lymphatic system where lymph passes from tissues to vessels, where it becomes progressively enriched in leukocytes (macrophages, DCs, and lymphocytes)

activation

stage of the lymphatic system wherein the lymph nodes trap the foreign antigen; lymphocytes interact directly w/ threat + undergo rapid activation/maturation/gain of effector function

systemic deployment

stage of the lymphatic system wherein activated lymphocytes exit the nodes, go into systemic circulation, and migrate directly to the peripheral tissues under attack

afferent inflow

antigens & enriched lymph fluid are delivered directly into the lymph node via this movement

efferent outflow

activated lymphocytes exit via this movement, traveling up the thoracic duct and empty into the superior vena cava

mainly tonsils, Peyer’s patches, appendix, GI + respiratory tract

MALT includes

cortex, paracortex, medulla

a lymph node can be divided into three anatomical regions

cortex

contains mostly B cells, macrophages, and follicular DCs arranged in

follicles

paracortex

populated largely by T lymphocytes and contains DCs that migrated from tissues to the node

medulla

site where lymphocytes exit (egress) the lymph node through the efferent lymphatics. Also, some activated plasma cells that secrete antibodies (ABs) to the circulation (thoracic duct) will reside here too

HEVs

Blood circulating naïve T lymphocytes enter the lymph node from blood vessels to the PARACORTICAL REGION of the lymph node by passing between this

FRCC

paracortex is rich in this network that guides T-cell movements and give them an ample opportunity to browse the surface of antigen-presenting DCs that appear to wrap themselves around the conduits

efferent lymphatics

what happens to T cells that browse the PARACORTICAL REGION of the lymph node but do not bind to an antigen

several day residency + differentiation

T cells whose TCRs do bind to an antigen on a dendritic cell that they encounter in the PARACORTICAL REGION of the lymph node will do what?

direct + indirect

B cell activation requires __________ engagement

BCRs

direct antigen engagement via ______ partially activates B cells

follicular DCs

indirect contact with ________ partially activates B cells

yes

do naive B cells also use blood vessels and HEVs to enter the lymph nodes? yes or no?

T cell-rich paracortex

once B cells get directly/indirectly become partially activated, where do they go?

non-immune cell

true nature of follicular DCs

TFHs

partially activated B cells engage with what in the PARACORTICAL REGION of the lymph node for a few hours until they get fully activated and undergo proliferation

germinal centers

Some activated B cells differentiate directly into short-lived plasma cells, but others re-enter the follicles in the cortical region to establish what?

4-7 days

establishment of the germinal center take place within

migration + proliferation

swelling is caused by an increase in the number of B lymphocytes due to

B cell proliferation + selection & memory B + long-lived plasma cell generation

what is happens in germinal centers?