Lymphoid tissue Flashcards
What are primary lymph tissues?
those sites that support the generation of functionally mature, but antigen naïve, T and B cells
(bone marrow and thymus)
What are secondary lymph tissues?
locations where naive lymphocytes reside while waiting to be activated by their specific antigens. These funnel antigens through them.
(e.g. Lymph nodes, Peyer’s patches, spleen)
What are tertiary lymph tissues?
sites of the body where the elimination of antigen takes place (the “battlefield”)
e.g. skin, GI, lungs, vagina
What are the cells in bone marrow responsible for the generation of new cells?
Pleuripotent stem cells
The hematopoietic compartment of the marrow is supported by what?
the bone marrow stroma
The bone marrow stroma is composed of what? (3)
reticular stromal cells, macrophages, and adipocytes
What is the function of stromal cells in the stromal tissue of bone marrow?
provide for cell-to-cell contact as well as soluble factors required for the differentiation of the hematopoietic cells
Where do B lymphocytes mature? From where to where?
Mature from outer to inner part of bone marrow
The differentiation of immature B cells to mature B cells takes place where?
Secondary lymphatic tissue
Where do T lymphocytes originate from? Where do they go to mature?
Bone marrow, go to thymus
Stem cells differentiate into what precursor of T cells?
Prothymocyte
Once in the thymus, the prothymocytes are called what?
Thymocytes
Where are autoreactive T cells deleted?
Thymus
Why does it not matter that the thymus degenerates in adults?
Once the T lymphocyte repertoire is established, T cell immunity is maintained by long-lived memory T cells and division of mature peripheral T cells.
Do thymocytes express TCR, CD3, CD4, or CD8 proteins?
No
True or false: during the development of thymocytes, there is a point where they express both CD4 and CD8
True
Once the T lymphocytes reach the thymus, what proteins are they expressing?
the TCR, CD3 and either CD4 or CD8 proteins
What are Hassall’s corpuscles?
Graves of dead thymocytes
What cells are the “teachers” of thymocytes? How do they do this (3)?
Cortical epithelial cells, which provide:
- Cell-to-cell contact
- Cytokines
- Peptide hormones
What ensures that lymph only moves in one direction?
One-way valves on lymph vessels
What tissues are the main immunologic responders?
Lymph nodes
The thoracic duct empties its contents into what?
Left subclavian
What vessles bring in lymph to lymph nodes? Away?
Afferent = bring in Efferent = take out
The cortex of lymph nodes has what type of cells? Paracortex? Medulla?
Medulla and cortex = B cells
Paracortex = T cells
What is the significance of B cells having to migrate past T cells in lymph nodes?
Increases chance that an activated B cell reacts with a Th cell
What are the B-cell rich areas of lymph nodes called?
Follicles
Primary follicles in lymph nodes contain what two cell types?
B cells and dendritic cells
Secondary follicles in lymph nodes contain what type of cells?
antigen-activated B cells and follicular dendritic cells
True or false: Dendritic cells are present throughout the T cell-rich areas
True
Where are macrophages found in lymph nodes?
mainly in the marginal sinus
What happens when lymph nodes encounter an antigen, and are enlarged?
Primary follicles morph into secondary ones
Do lymph nodes that have been exposed to antigen totally morph back to their original state?
Yes
What is the function of called high endothelial venules in lymph nodes?
Express specific adhesion molecules which lymphocytes can bind using homing receptors to enter the lymph node from the blood
What is the general role of the spleen? How does it do this?
Filter blood
exposes lymphocytes in white pulp to blood-borne antigens
Surrounding the central arteries and penicilliary arterioles in the spleen is what?
a cuff of lymphocytes, most of which are T cells (PALS)
Does splenic lymphoid tissue have high endothelial cells?
No, but has analogous structures
Most pathogens that we encounter occur where?
at mucosal sites such as the lungs, gastrointestinal tract and genitourinary tract.
Do MALTs have specific B and T cell regions?
No
What are Peyer’s patches?
MALTs in the ileum, where B cell follicles are surrounded by a zone that is rich in T cells
Are there high endothelial venules in Peyer’s patches?
yes
What is the function of the “M” cells in Peyer’s patches? What gives them this ability?
transport proteins and microorganisms from the intestinal lumen into the lymphoid tissue
Have microfolds
What allows B and T cells to continue to survive despite not having encountered antigens?
secondary lymphoid tissues provide sustaining signals to lymphocytes
What directs T cells, B cells, marcophages, and dendritic cells to their location within a lymphoid tissue? What produces these?
Chemokines, produced by stromal cells of lymphoid organs
What is the general function of tertiary lymphoid tissue?
to complete an immune effector response
Can any tissue be a tertiary lymphoid tissue? Which tissues are generally tertiary lymphoid tissues?
Yes, but generally skin and mucosa
What allows for the deposition of macrophages, B cells, T cells etc in specific tissues?
Adhesion proteins that are expressed on blood vessel endothelial cells
What are the dendrictic cells that are present in the stratum spinosum of the skin? What happens when these cells encounter an antigen?
Langerhans cells
They stop expressing cell adhesion molecules and migrate out
the vast majority of B and T lymphocytes that are present at tertiary lymphoid sites are of what type?
Memory cells
What must happen to Langerhans cells before they can present antigen to T cells?
Migration to lymph node and maturation to mature dendritic cell
Antigen that has been carried from the tissues to the lymph node via the lymph encounters what cells?
Macrophages but also other antigen presenting cells
B lymphocytes that migrate into the lymph node have to pass by what cells on their way to the B cell-rich follicles?
T helper cells
What can happen to B cells that express antigens to T cells in lymph nodes?
Differentiate into plasmablasts right away to express less specific antibodies or migrate to B cell follicles to proliferate
What type of cells are in the germinal center of secondary follicles?
proliferating, antigen-specific activated B cells
What is the time frame for B cell proliferation when activated?
6-8 hours
What ultimately happens to the B cells that form the germinal center of lymph tissue?
differentiate into plasma cells and secrete high affinity antibody OR become memory cells
What are the two major sites of antibody production/excretion?
Medulla of lymph node
Bone marrow
Why do lymphocytes have to be circulated in the body?
. Since a relatively few copies of naïve lymphocytes exist for any given antigen, recirculation allows a greater probability for those lymphocytes to contact an antigen presenting cell and become activated.
What is lymphocyte homing? What molecule is this process dependent on?
the propensity for lymphocyte populations to take up residence preferentially in certain lymphoid organs or tissues
Homing is dependent upon specific “addressins” expressed by lymphocytes that allow the cells to bind to the site that specifically binds those addressins.
What is the migratory pattern of Memory cells, and why is it different from naive lymphocytes?
Tend to circulate or accumulate in tertiary tissue, because they need to be in places where antigen is encountered
. An IgA response that occurred in a lymph node or in the skin would not be optimally effective. Why?
IgA is specialized for mucosal secretions.
