Flashcards in Lymphoid II Deck (49):
How and where do naive lymphocytes enter lymph nodes?
They enter at the HEV through ligand receptor mediated specific surface interactions (with epithelial cells)
When activated what do lymphocytes do?
Produce effectors and memory cells
What two places might plasma cells mature?
In the lymph nodes or in the periphery
In what part of the lymph nodes do plasma cells mature (if they mature in the nodes?)
In the medullary cords
How does mature antibody escape the lymph node?
Through the sinuses and into the efferent lymphatic; syllabus only says "eventually to bloodstream"
What type of plasma cells mature outside the lymph nodes? What type of cells are they specialized for?
Ones that secrete IgA antibodies; mucosal cells
What are some examples of places where plasma IgA cells might go?
mammary and salivary glands
What determines migration pattern of plasma cells?
Changes in receptor expression during activation
Where do effector T cells disseminate to?
to the periphery, specifically areas where the antigen entered the body
what happens to effector T cells during differentiation to affect their dissemination?
they gain receptors for peripheral post capillary venules and vessels in inflammatory sites
what path do T cells take when searching for their antigen in the periphery?
through connective tissue and epithelia; if they don't find their antigen then they proceed back into the lymphatic system going through secondary lymphatic organs
What two general types of tissue are found in the spleen
red pulp and white pulp
What is the red pulp?
it accounts for most of the tissue and has large amounts of blood
What is the white pulp?
Accumulations of lymphoid tissue; stains basophilic in section; taken as a whole it makes up the largest lymphatic organ in the body
What does the red pulp do?
filtration - removing foreign matter from the blood
removes organelles from reitculocytes
removes old or damaged erythrocytes
Where do you find the marginal zone?
at the border of the white and red pulp
which type of lymphatic vessel do you find in the spleen?
efferent lymphatics; because it does not have both, it does not filter lymph
What's special about the vasculature of the spleen?
Open system after capillaries, blood deposited into the extravascular space for filtration
Where do you find the Largest vessels in the spleen?
in the connective tissue trabeculae
where do you find white pulp in the spleen?
surrounding the central arteries; this is called the periarterial lymphatic sheath (PALS) and contains primarily T cells, but also has dendritic (APC) cells; also contains follicles
what do you find in the follicles of the spleen? which type of pulp are they?
white pulp, B cells; these displace the central artery, have germinal centers and are found in less density in the elderly
what do you find in the red pulp?
an anastomosing network of venous sinuses
Billroth's strands (a.k.a. splenic cords)
what characteristics of the venous sinuses do we need to know?
basement membranes; endothelial cells are long, plump and aligned parallel to direction of flow
what's special about Billroth's strands?
reticular connective tissue between sinuses; sort of a web through which blood must flow to reach sinuses, contains macrophages and plasma cells; ALL blood cells go through
what comprises the structural support for the spleen?
trabeculae made up of Type I collagen
reticular fibers abundant in Billroth's strands and white pulp
Note: not found within the blood sinuses (unlike lymphatic sinuses)
2nd note: basal lamina stains black in silver stain as well
generally, what is the blood flow through the spleen?
central artery -> penicillar arteries -> very small capillaries -> EV space -> sinuses
what is special about penicillar arteries?
they are surrounded by macrophages and plasma cells
found at the marginal zone
what happens to the lymphocytes as they enter the EV space?
they are shunted to the white pulp to search for their antigen
what special properties does the endothelium of the venous sinuses in the spleen have?
discontinuous basement membrane with thin slits that blood cells must crawl through to reenter circulation; macrophages and neutrophils hover just outside of the endothelium
this serves to prevent damaged or old cells from reentering the circulation
where do venous sinuses converge?
into the trabculae "central" vein
what does collodial carbon reveal in animals?
what is retrieved from RBC's if consumed by macrophages?
what happens to reticulocytes as they near the endothelium in the spleen?
their remaining organelles compressed into a pocket near the plasma membrane and are removed right before entering the circulation
what type of organ is the thymus?
primary lymphoid organ
what is produced in the thymus?
immunocompetent T cells
what's special about the type of environment provided by the thymus (for T cells) and the bone marrow (for B cells)?
they are free of antigens; this means that the cells that they produce are immunocompetent by naive
when does the thymus begin to involute? what is the function tissue replaced by?
puberty; fat cells;
what is the tissue structure of the thymus?
septa (NOT TRABECULAE) divide the lobes into incomplete lobules;
a darkly staining outer cortex and a lighter staining inner medulla, reflects density of lymphocytes
what's another name for lymphocytes in the thymus?
what do you find in the septa of the thymus?
larger vessels and connective tissue cells including numerous mast cells
what provides the fine support structure of the thymus? what else do these cells produce?
highly stellate epithelial cells (epithelial reticular cells);
factors essential for proper T cell development
where does T cell maturation happen? what's the physical path taken by the T cells?
cortex; exit post capillary venules near the cortico-medullary junction and then migrate to the outer cortex
what types of cells do you find in the thymus?
epithelial reticular cells
dendritic cells (at the C-M junction)
what stages do developing T cells go through?
3rd: development of specific receptors (antigen and migration control) (controlled by factors from epithelial reticular cells)
4th: selection and autoreactive cells (90% fail and are phagocytosed)
how does the thymus limit exposure to antigens?
no afferent lymphatics;
blood thymus barrier - composed of continuous tight junctions, zonula occludens, b/w endothelial cells; macrophage security surrounds that; wrapped by reticulocytes (also with zonula occludens)
what is special about the medulla of the thymus?
little differentiation happens here
composed primarily of epithelial reticular cells (fewer thymocytes)
many connective tissue cells (macrophages, mast cells, plasma cells)
no blood-thymus barrier here
contains round epithelial cysts - Hassal's corpuscles
where do you find Hassal's corpuscles?
medulla of the thymus
aging effects on thymus?
functional decline (fewer T cells being produced)
more autoimmune disorder
decline in function of APC
increase in latent disease activity
THEREFORE, vaccinations are more important to the elderly