lymphoid system Flashcards
Lymphoid stem cells are produced by the ___ __ ___ and ______ in the very young fetus
yolk sac mesoderm
fetal liver
the cells involved in the _____ immune response(_____, ___ ___ __) are localized and concentrated in anatomically defined organs and tissues that constitute the lymphoid system. they are also the sites where foreign antigens are transported and concentrated
adaptive
lymphocytes
antigen-presenting cells
In older fetuses and neonates, the _________ is the main source of lymphoid stem cells
bone marrow
the classification of lymphoid organs and tissues is based on
- the level to which they participate in the maturation of lymphocytes
- provision of a suitable environment for the interaction between foreign antigen and antigen-sensitive T and B lymphocytes
central or primary lymphoid organs
Bursa of Fabricius
Bone marrow
thymus
peripheral or secondary lymphoid organs
lymph nodes
spleen
mucosal and cutaneous lymphoid tissues
central lymphoid organs and tissues (_____, _____, ______, and _______) regulate production and maturation of lymphocytes
thymus
bone marrrow
Peyers patches
Bursa of fabricius
“one cel, One specificity”
generate lymphocytes that are individually different to meet the threat posed to an animal or individual by the large number of microbial pathogens
central lymphoid organs develop early in embryonic life and ___ after puberty, except bone marrow
involute
mature lymphocytes acquire ____ ____ _____ and other _____ ______ and learn to ______ between ____-_____, which are tolerated and foreign antigens, which are not, ie, “self vs nonself”
specific antigen receptors
phenotypic characteristics
discriminate
self-peptides
maturation and differentiation of lymphocytes occur
independent of foreign antigenic stimulation
upon removal early in life, there is loss of lymphocytes, resulting in loss of ____ ______
immune responsivness
the thymus is the site of
Tcell development and maturation
In ___, ___,___, ___, and _____, the thymus extends up the neck as far as the thyroid gland
horses, pigs, sheep, cattle, and chickens
the ___ has a rich blood supply and efferent lymphatic vessels that rain into mediastinal lymph nodes
thymus
Cortex
contains about 85% of the total thymocytes
during different stages of thymocytes maturation in the cortex they acquire ____ ____ (TCRs) and other _____ and ______ characteristics of mature T cells
antigen receptors
functional and phenotypic
as lymphocytes mature, they migrate toward the
medulla
medulla
sparsely populated with mostly mature lymphocytes
a network of epithelial cells, macrophages, and dendritic cells are found throughput the thymus especially at the
corticomedullary junction
T cell selection
developing lymphocytes acquire TCRs by gene rearrangement: TCRs are selected for both self MHC restriction and self -tolerance
self tolerance
ability to distinguish between “self” and “nonself” by self MHC-self-peptide complexes expressed on thymic stromal cells
The thymus induces the death by _____, of thymocytes whose TCrs react strongly with ________________. asa result, more than ____ of developing thymocytes die by _____.
apoptosis
self antigen MHC- complexes
95%
apoptosis
T or F
in humans, thymic involution begins at puberty and continues throughout adulthood
T
thymic involution begins within the ___ which may disappear completely, whereas _____remnants persist.
cortex
medullary
____ ____ is related to corticosteroid sensativity (lysis) of the immature cortical thymocytes
cortical atrophy
Bursa of fabricius
is a lymphoepithelial organ found in birds but not in mamals; it is a sac-like structure dorsal to the cloaca
the bursa reaches maximum size ________ after hatching, followed y gradual involution; by the times the bird reaches sexual maturity (_____), only ___ vestiges remain of the BF and thymus
1-2 week
6 months
atrophied
Majority of B cells (_____) die through_____
90-95%
apoptosis
apoptosis
a reflection of negative selection of self-reactive B cells
Mature B cells begin to migrate from the bursa to the peripheral lymphoid organs________
a few days prior to hatching
the bone marrow is the site of generation of
all blood circulating blood cells and a fat depot
in mammals , bone marrow is both a ___ and ___ lymphoid organ
primary and secondary
what two compartments is bone marrow divided into
hematopoietic and vascular compartments
hematopietic compartment
contains precursors of all the blood cells (self-renewing stem cells) as well as stromal cells, macrophages and lymphocytes
in most mammals, the bone marrow is the site of early events in
B cell development
stromal cells
- secrete various cytokines that are required for B celldevelopment
- selection of immature B cells
Immature B cells that acquire ___________ receptors are allowed to die
self-reactive receptors
the bone marrow contains numerous long-lived plasma cells that produce ___ fro many months or years
antibodies
these plasma cells are produced in ____ lymphoid organs as a result of antigenic stimulation of B cells and then migrate to the bone marrow
peripheral
peyers patches
are aggregations of lymphatic nodules that are found in the walls of all three segments of the small intestines
Two types of PP have been described:
- numerous discrete lymphatic follicles that function as peripheral lymphatic organs
- single large ileal PP
peripheral lymphatic organs contain
B cells, T cells, antigen- presenting cells
they persist throughout the life of the individual or animal
single large ileal PP
in ruminants, pigs and dogs and functions as a primary lymphatic organ. it is the siteof early B cell development
single large ileal PP undergoes involution by
1 1/2 years of age
peripheral lymphoid organs
arise late in fetal life and persist through adulthood.
removal of any of the secondary lymphoid organs _____ significantly reduce an individual or animals immune capacity
does not
secondary lymphoid organs are the sites where mature lymphocyte responses to foreign antigens are ____ and ____
initiated and develop
the 3 major portals of antigen entry into the body
skin
respiratory tract
gastrointestinal tract
blood borne antigens are filtered by
the spleen
tissue antigens are carried by lymphatic fluid to regional
lymph nodes
lymph nodes
are the only lymphatic organ with both afferent and efferent lymph vessels
lymph nodes are the sites where immune responses to antigens entering the body via the ___ and ___ or from _____ and ______ are initiated
skin
mucosa
parenchymal organs
connective tissues
all lymph nodes eventually drain into the _____ system and back to the ______
thoracic duct
peripheral blood
lymph nodes are made up of
cortex
paracortex
medulla
efferent lymphatic vessel
lymphoid cortex
B cells are organized into primary and secondary follicles here
primary lymphoid follicles
follicles without germinal centers; they contain mostly resting mature B cells, follicular dendritic cells and macrophages
secondary lymphoid follicles
primary follicles with germinal centers
germinal centers
develop in response to antigenic stimulation of B cells; thus B cell proliferation, selection of B cells producing high affinity antibodies and generation of memory B cells
paracortex
contains mostly T cells, some macrophages and dendritic cells. lymphocytes enter the node from the circulation through the high endothelial venules in the paracortex
medulla
contains mostly macrophages, antibody-secreting plasma cells and lymphocytes
efferent lymphatic vessel
lymph leaving via the efferent lymphatic vessel contains newly secreted antibodies, effector lymphocytes and mostly naive lymphocytes that migrated from the blood into the lymph node through the paracortical HEVs
spleen
the largest of the secondary lymphoid organs and is therefore the major organ in the body in which antibodies are produced
the spleen is the major site of immune responses to _______; there fore ____ can lead to an increase in blood-borne microbial infections
blood-born antigens
splenectomy
two main types of spleen tissue
white pulp
red pulp
white pulp
lymphoid tissue of white pulp is organized around the central arteriol to form the periarteriolar lymphoid sheath(PALS)
T cells are mostly found where in the spleen
central arteriole
bcells in the spleen are mostly found
in primary and secondary follicles
spleen follicles also contain
macrophages, and follicular dendritic cells
red pulp
contains macrophages, some activated B cells and plasma cells
it is a storage site for erythrocytes, platelets, and granulocytes
Macrophages in the red pulp ____ old____ and ___ and also clear the blood of microorganisms and other particles;
phagocytose’
platelets
RBCs
T or F
the spleen is the major site for the phagocytosis of antibody coated (opsonized) microbes
True
Marginal zone of the spleen
separates the whit pulp from the red pulp. It contains macrophages and some lymphocytes
Mucosal associated lymphoid tissue
comprises all lymphoid cells present as either solitary or aggregated nodules in epithelial, lamina propria and submucosa of the GI tract, respiratory tract and genitourinary tract
what are the main sights of MALT
gut-associated lymphoid tissues
bronchial -associated lymphoid tissue and genitourinary tract
cutaneous immune system
GALT consist of lymphoid tissue in
lamina propria of the intestines
peyer’s patches
appendix
tonsils
cutaneous immune system
consist of lymphocytes ad accessory cells in the epidermis and dermis that respond to enviromental antigens
lymphocyte recruitment
is the continuous movement of lymphocytes from one lymphatic organ or tissue to another via the blood and lymph, and is activated to peripheral inflammatory sites
a lymphocyte may recirculate from the blood to the tissue and lyph and back again as often as ___ times per day
1-2
the predominate lymphocytes in blood are
T lymphocytes
high endothelial venules (HEVs)
extravasation of naive lymphocytes from the blood into a peripheral lymph node occurs selectively at modified post capillary venules within the paracortex of the lymph node here
HEVs are present in each of the _____ lymphoid organs but not in the ____
secondary
spleen
HEVs possess _______; they are cytokine-activated cells that express a variety of adhesion molecules not found on the flat resting endothelial cells of ordinary venules
cubodial (plump) endothelial cells
the recirculation patterns of naive T lymphocytes is governed by the combination of adhesion molecules (_____) and chemokine receptors (____) that they express
L-selectin
CCR 7
T or F
even though B cells recirculate, only a small fraction of blood lymphocytes are B cells
T
