The Lymphoid System Flashcards
what are the primary lymphoid organs
bone marrow and thymus
what are the primary lymphoid organs the major site of
lymphopoiesis
-here, lymphocytes differentiate from lymphod stem cells, proliferate, and mature into funtional cells
where do T cells undergo most of their development
where do B cells
T=thymuc
B=bone marrow
where do lymphocytes acquire their repertoire of specific antigen receptors in order to cope w/ antigenic challenges
primary lymphoid organs
-bone marrow and thymus
do developing t and b cells respond to foreign antigens in the primary lympoid organs
no
what is hematopoiesis
the process by which all red and white blood cells are produced
where does hematopoiesis occur in adults
the bone marrow of the sternum, vertebrae, iliac bones, and ribs
hematopoiesis occurs in the yolk sac of the fetus and is then taken over by the _____, followed by the ____
spleen and liver
bone marrow
what is red marrow
marrow in which hematopoiesis occurs
what are stromal cells (reticular cells)
supoprting meshwork of fibroblasts and they secrete reticular fibers which red and white cells develop
aka hematopoietc cords
red and white cells exit the bone marrow to enter the circulation via…
a dense netowrk of vascular sinuses
what are all bone marrow cells dervied from
a common self-renewing stem cell whicih develops into a pluripotent stem cell
what do pluripotent stem cells differneitate into
either a myeloid of lymphoid precursor cell
what do the myeloid progenitors develop into
gives rise to all blood cells except B, T, and NK cells
what do the lymphoid progenitors develop into
B, T, and natrual killer cells
what are colony stimulated factors
factors that promote growth of lineage of WBCs
what act on stem cells to stimulate blood cell formation?
what are they produced by?
cytokines such as colony stimulated factors
and a host of cytokines referred to as interleukins
-produced by stromal cells, monocytes, and helper lymphocytes
what is IL3 important in
hematopoiesis
what is neupogen
granulocyte CSF
used with patients with low neutrophil cell numbers
can be used for aids and cancer patients
what are reticulocytes
erythrocyte stage right before full maturity
where is the thymus located
in the mediastinum in the center of the chest above the great vesssels of the heart and consists of 2 lobes which are further divded into locules by fibrous septae
where does the majority of T cell maturation occur
outer cortex of the thymus
what does the cortex contain, what cells
densely-packed T cells
macrophages
APCs called dentritic cells
what speciliazed cells form the structural framework of the thymus
reticular ep cells aka cortical thymic ep cells (cTEC)
the cortical thymic ep cells DO NOT secrete reticular fibers, how can they support developing T cells?
only with their cell membrane
what are hassall’s corpuscles and wehre are they located
tightly packed whorls of ep cells located in the medulla
significance is unknown
how do the hassall’s corpuscles change after pubert
decrsease in number but increase in size after puberty
how can the hassall’s corpuscles serve as a valuable radiological marker
calcify later in life, show where the thymus is
lymphocytes destined to develop into T cells begin their maturation int he bone marrow and leave while they are….
- they then go to the….
- what are they called
still very immature, then go go to the thymus cortex and complete their differentation
known as thymocytes
what do the most undifferentiated T cells do when they enter the thymus
proliferate, mature, and begin migrating toward the medulla, where they eventually enter the ciruclation
-they DO NOT express T cell receptors, CD4 or CD8 molec
what is the purpose of cTEC (cortical thymic ep cells)
- to secrete thymic homromes such as thymopoeitin, thymosin, and interleukin 7 which are though tot promote T cell matruation
- to bind to, and positively select for T cells with the ability to recognize and bind to self MHC molecules
what are the thymic hormones
thymopoietin
thymosin
interleukin 7
what happens to T cells that are unable to bind to MHC molecules
elminated by apoptosis
what happens to the cellular DNA, nucleus and cytoplasm during apoptosis
what happens to the cell for macrophages to phagocytose these
cellular DNA is fragmented
nucleus and cytoplasm condense
dying cell often framents into membrane bound apoptic bodies that are rapidly phagocytosed and digested by macrophages
what is positive selection
if a T cell matures which cannot recognize self MHC, it will be ineffective in responding to an antigenic stimulus and will be apoptosed
where does negative selection take place
cortico-medullary junction
what are dendritic cells, why are they important
specilaized APCs derived from the bone marrow
play a role in binding to and eliminating cells that bind to self MHC with an inappropriately high affinity
what is negative selection
binding affinity to MHC alone, nothing with what antigen is
-cells with an inappropriately high affinity that bind to self MHC are eliminated through apoptosis
why is negative selection necessary
the T cells that bind too strong to MHC can develop into autoreactive cells which are cells tat can recognize elf antigens as foreign and attack them
how much % of all T cells in the thymic cortex are elminiated by positive and negative selection
50%
which structure in the thymus has the structural specilializations that prevent antigen entry
thymic cortex, NOT medulla
what is the blood/thymus barrier
the thymic cortex with ep cells slapped on that prevents antigen entry
why must antigens need to be kept out of the thymus and bone marrow while T cells are maturing
bc any antigen which does not enter may interfere w/ T cell development and the T cells will NOT be able to recognzie that antigen and ignore them to be left in the thymus
what are the speciliaztoins which constitute the blood/thymus barrier
- tight junctions btwn endothelial cells and a thick endo cell basement membrane
- a thin layer of ep cells which completely encloses the thymic cortex and vascular basement membranes
the absense of afferent lymphatic vessles does what to the antigens
contributes to the lack of antigens in the thymic cortex
what happens to the thymus with again
undergoes partial involution (gets smaller)
but it continues to produce T cells throughout the life of the indiv
what are the 2ndary lympoid organs
lymph nodes
spleen
mucosal and cutaneous immune systems
which organs do the immune cells come into contact w/ antigens
2ndary lymphoid organs
what form can lymphatic tissues be found as
dispersed cells
aggregates of cells situated beneath epithelia
what are some examples of mucosal and cutaneous immune systems
what do these tissues contain
tonsils in the oral cavity peyer's patches in GI tract (GALT) immune cells in upper resp tract and bronchi (BALT) conjunctiva (CALT) skin (SALT)
contain T and B cells, macrophages and APCs
what ist the langerhans cell
an important APC in the skin
what is an example the body’s response to antigenic stimulation (lymphatic tissue developing anywhere in bod)
uveitis : infl disease where lymphocytes and other immune cells wreak havoc on uvea and retina
colitis: occurs in distal ileum
whta happens to the antigen if it escapes elimination in the subepithelia areas
it will be taken up by draining lymphatic vessels which are supplied with antigenic filters (lymph nodes)
what are lymph nodes
wehre are they located
what are they surrounded by
small nodular aggregares of lymphoid tissue
situated along lymphatic channels
surrounded by a fibrous capsule that is pierced by numerous afferent lymphatic vessels
what do afferent lymphatic vessels do
what do efferent lymphatics exit at
bring lymph fluid and cells into the node which course through the node as nodular sinuses and eventually join efferent lymphatics which exit the node at the hilus
why are subcapsular sinuses leaky
to allow both cells and fluid to freely exchange btwn the sinus lumen and the parenchyma of the node
-to create back pressure
what is the primary cell type in diffuse lymphatic tissue
what about nodular
diffuse=T cell
nodular=B cell
what do radial trabeulae together with reticular fibers do
support the various cellular compartments w/in the lymph node
wehre is the B cell and T cell area in lymph nodes
what does the central medulla contain
B cell area is the outer cortex
T cell area is the inner or para cortex
central medulla contains the differentiation products of lymphocyte activation such as plasma cells
where are APCs especially prevalent in in the cortex
present throughout but especially prevalent in the outer cortex
-the cells are referred to as interdigitating or dendritic cells
where is the bulk of lymphoid tissue found
outer and inner cortices
what are medullary cords
some lymphoid tissue that extend into the medulla where they are found along strands of connective tissue fibers
what are medullary cords separated by
large sinuses and contain most of the plasma cells in the lymph node
macrophages are present in lymph nodes and are especialy present in…
the medulla
what cells are present in primary or secondary follicles
B cells in the outer cortex
what are primary follicles
dense, round, or ovoid aggregations of resting B cells
unstimulated
what cells do secondary nodules contain
activated B cells
what is the germinal center
what cells does it contain
pale staining central region which contains activated, enlarged, proliferating B cells as well as B cells that are differentiaing into plasma cells
what surrounds the germinal center
what does it contain, how does it stain
the mantle zone
smaller, resting B ceslls that looks and stains like primary nodules
where are APCs primary located
diffuse tissue, but also in nodular
which tissue type of B cells in
what about T cells
B=nodular/flolucullar tissue
T=diffuse tissue
where will antigens that stimulate an antibody response enter? what will they bind to? what will they induce?
- enter the primary follicles
- bind to B cell cantigen receptors
- induce secondary follicle formation and plasma cells production
where will antigens that stimulate a T cell response be taken up by?
how will this activate a T cell response?
taken up by dendritic cells in the cortex, that will bring these antigens into the T cell region of the inner cortex and activate a T cell response
what cells will seek out and destroy antigens in the tissue
activated T cells (helper) and cytotoxic T cells
what do T helper cells do
provide help to B cells that reponse to T dependent antigens
what do follicular dendritic cells do
trap antigens complexed to antibodies or complement and display them on their surfaces for recognition by B lymphocytes
-play an important role in the selection of activated B cells whose antigen receptors bind the displayed antigens w /high affinity
what are the palpable lymph nodes
cervical
inguinal
auxillary lymph nodes
what is the englargement of a lymph node referred to as
lymphadenopathy
what is erythema
redness due to capillary congestion
what can cause the pre-auricular node to swell (adenopathy)
endoviral infection
less common in bacterial infections
what type of infection is chlamydial conjunctivitis
-almost always exhibits a palpable pre-auricular node
bacterial inclusion
if an antigen fails to be filtered out by the lymph nodes, how is it filtered
enter the blood stream and is filtered by the spleen
what is the spleen the major site for
phagocytosis of antibody-coated microbes
without the spleen what would one be more susceptible to
infectious encapsulated bacteria
what support the variety of cells in the spleen
connective tissue capsule that sends trabeculae into the parenchyma of the organ and the reticular fiber framework
what are the 2 main types of tissue in the spleen
red pulp: sinusoids and rest of blood cells
white pulp: WBCs, T and B cells
what is the functinon of the red pulp
what is the function of the white pulp
red: mainly involved in clearing the blood of old and dying blood cells and particulate matter
white: contains lymphatic tissue capable of responding to antigenic stimulation
where is the bulk of lymphatic tissue located around
located around small arterioles so it is called periarteriolar lymphatic sheath (PALS)
where are the Tcell and B cells areas of PALS
T cell areas being close to central arteriole
B cell areas being found more peripherally
how are the B cell areas of PALS organized
as theyare in lymph nodes: w/ areas of primary and/or secondary follicles present, depending on state of antigen
what is the marginal zone
the PALS are surround by a rim of lymphocytes and macrophages called the marginal zone where it is thought that antigens first enter the white pulp
where do the arterioles ultimately end
directly or indirectly in vascular sinuses w/in the region of the red pulp where macrophages clear the blood of old and dying cells
what do blood cells that are not cleared by macrophages do
re-enter splenic venules and exit the spleen by way of the splenic vein
what encapsulated bactera does the spleen remove
act removal of encapsulated bacteria haemophilus influenza and streptococcal pneumonia
how to lymphocytes circulate throughout the body, tissues, and lymph compartments
insinuating themselves btwn the endothelial cells of post capillary venules by a process called diapedesis
what do post-capillary venules have on their cell wall isntaed of squamous endothelial cells for the migration of lymphocytes into lymph nodes, spleen and mucosal lymphoid tissue
lined by high-walled cuboidal endothelial cells referred to as high endothelial venules (HEV)
how are lymphocytes guided to the HEVS
by their interaction w/ vascular addressins on the surface of the endo cells (act as homing beacons for the lymphocytes)
how to lymphocytes bind to addressins
integrins which also play a role in tissue migration of cells during embryogeness, tumor metastasis, and wound healing
do lymphocytes need high endo-walled vessels to enter nonlymphatic tissue?
no
