Flashcards in Lymphoid Tissue_BTED Deck (103):
What is the organisation of the lymphoid tissue?
What type of cells does the primary organisation of lymphoid tissue contain?
Contain cells undergoing lymphocyte maturation process
What is the primary organisation of lymphoid tissue made of?
2) Bone Marrow
What type of cells does the secondary organisation of lymphoid tissue contain?
Contain antigen reactive cells in the process of circulating through the body
What is the secondary organisation of lymphoid tissue made of?
1) Lymph nodes
What does adaptive immunity depend on?
Cell division to produce large number of lymphocytes with specificity for a particular pathogen (or antigen) and thus takes 3 - 5 days to develop a significant response.
What do lymphocytes do?
Abile to kill or disable pathogens either by a cellular response (T lymphocytes or T cells) or a humeral response (B lymphocytes or B cell) or both
What does the adaptive immunity do?
Amplifies some of the mechanisms of the innate response.
What is the adaptive immune response controlled by?
Innate response as T lymphocytes require services of Antigen Presenting Cells for activation
What is produced in the bone marrow?
Lymphocytes of the adaptive immune system
What is the lymphocytes of the adaptive immune system in teh bone marrow produced from?
From haematopoietic stem cells along with the cells of the innate system.
What does the cells of the adaptive immune system do?
1) Form specialised lymphoid tissue
2) Constitute a significant component of other tissues such as GI tract.
Name the major lymphoid organs.
2) Bone Marrow
3) Lymph nodes
5) Mucosa associated lymphoid tissue (MALT)
Where is the thymus situated?
In the anterior mediastinum
What is thymus for?
Site of maturation of immature T lymphocytes
What is bone marrow for?
1) The home of lymphocyte stem cell
2) Site of B lymphocyte maturation
Where is the lymph node found?
At the junctions of major lymphatic vessels
What are lymph nodes for?
Sites where both T and B lymphocytes may interact with antigen and APC from the circulating lymph, leading to lymphocyte activation and cell division
Where is the spleen located?
Left upper quadrant of the abdomen
What is the spleen for?
Location where T and B lymphocytes may interact with blood borne antigen and undergo stimulation and cell division
What does the MALT include?
1) Tonsils and Adenoids in the oropharynx
2) Peyer's patches and Lymphoid aggregates of the small and large intestines respectively
3) Diffuse population of lymphocytes
4) Plasma cells in mucosae of the GI, respiratory and genitourinary tract
What does the MALT do?
Respond to antigens entering the body through these mucosae.
How do primary lymphoid tissues recognise antigen?
Immature lymphocytes acquire receptors
How do secondary lymphoid tissue work?
Lymphocytes are activated in response to antigen
Most circulating lymphocytes are what and are measured to be how big?
6 - 9 micrometer
How big are large lymphocytes?
9 to 20 micrometer
What do small lymphocytes look like under a microscope?
Round to ovoid nucleus occupying about 90% of cell volume with a thin rim of Basophilic (bluish) cytoplasm
What happens when an antigen binds to a lymphocyte surface receptor?
Lymphocyte will be activated and a specific response to that antigen is triggered.
What does the B Cell Receptor comprise of?
Accessory molecules for B cells and T cell receptor for T cells
What is the ability of antibody to bind to antigen determined by?
By physicochemical properties of antibody.
- Shape and electrical charge of the binding site of the antibody must be complementary to the antigen
- Closer fit, stronger the bond
What does the T cell receptor bind to?
Major Histocompatibility Complex
What happens during maturation of lymphocytes?
Alternate components of the antigen binding part of the antigen receptor genes are spliced together (rearranged) in a random fashion.
Where do the immature T lymphocytes migrate from and to?
- From: Bone marrow
- To: Thymus where they develop into mature T lymphocytes
What does the process of maturation of T lymphocytes include?
- Rearrangement of TCR genes
- Acquisition of the surface receptors and accessory molecules of the mature T cell
What happens once mature T lymphocytes are formed?
- Have ability to react with 'self antigens' are removed by apoptosis, creating a state of self tolerance.
- It then populates the secondary lymphoid organs and from there continuously recirculate via the bloodstream.
What are the different subsets of T cells?
1) T helper cells
2) Cytotoxic T cells
3) Regulatory T cells
4) Memory T cells
5) Gamma - Delta T cells
What does the T helper cells do?
- T lymphocytes 'help' other cells to perform their effector functions by secreting a variety of mediations known as interleukins.
- Initiate/coordinate immune response
What does the T helper cells help?
1) B cells
2) Cytotoxic T cells
Name the subdivision of the T helper cells
What does TH1 cells do?
- interact with cytotoxic T cells, NK cells, macrophage in cell mediate immune response
- control intracellular pathogens
What does TH2 cells do?
1) Interact with B lymphocytes
2) Essential for initiating antibody mediated immune responses that control extracellular pathogens
What does TH17 do?
Modify and augment certain types of acute inflammation
What surface markers does T cells express?
And T cell receptor
Name the properties of Helper T cells.
1) T cells that also expressed CD4 markers.
2) these cells are subdivided by their ability to secrete cytokines
CD4 interact with MHC2 molecule which restrict the MHC2
What are CD markers?
Specific markers that relates to antigen expressed at different stages of their differentiation
What do TH1 cells synthesise?
What do the other group TH2 cells synthesise?
What are special about Cytotoxic T cells?
Express CD8 markers.
CD8 markers interact with MHC 1 molecule and thus MHC 1 is restricted.
What do cytotoxic T cells do?
Kill other target cells such as virus infected cells, cancer transformed cells, cells infected with intracellular microorganism, parasites and transplanted cells
What are regulatory (suppressor) T lymphocytes?
Phenotypically diverse population of T lymphocytes that can functionally suppress and immune response to foreign and self antigen
How does Regulatory T cells suppress an immune response to foreign body?
by influencing the activity of other cells in the immune system
What surface markers does regulatory T cells have?
In order for regulatory T cells to get peripheral tolerance what marker do they need?
FOXP3 marker is needed to diminish the ability of T lymphocytes to initiate an immune response. The FOXP3 marker indicates an expression of forkhead family transcription factor that are characteristic of many T cells
What are gamma delta T lymphocytes?
Small population of T cells that possess a distinct TCR on their surface made of one gamma chain and one delta chain. Contain a CD8+ marker and act like NK cells at epithelia
Most other TCR are composed of what?
Two glycoprotein chains called alpha and beta TCR chains
Where do the gamma delta T lymphocytes develop and migrate into?
Develop in thymus
Migrate into various epithelial tissue (e.g. Skin, oral mucosa, intestines and vagina)
Once colonised an epithelial tissue, they do not recirculate between blood and lymphatic organs
Where is Gamma delta T lymphocytes positioned?
At the interfaces of the external and internal environment
What do Gamma Delta T lymphocytes do?
1) Function as first line of Defence against invading organisms
- encounter antigen on the surface of the epithelial cells even before it enters the body
Name the antigen presenting cells
1) Monocytes (blood)
2) Macrophage (tissue)
3) Macrophage derived
4) Thymic epithelium derived
5) Fibroblast derived (follicular dendritic cells nodes)
6) B - cells
Name the subdivision of B lymphocytes
B memory cell
Plasma cell antibody factor
Where are B cells (undifferentiated and differentiated) found?
What do B lymphocytes do?
1) Involved in the production and secretion of the various circulating antibodies, also called immunoglobulin (Ig), the immune proteins associated with Humoral immunity
2) B cell express membrane bound forms of immunoglobulin called B cell receptors that serve as antigen binding site.
3) express MHC2 molecules on cell surface
What happens to the BCR isotope during differentiation
BCR isotope switches from immunoglobulin M (IgM) in immature B cells to immunoglobulin D (IgD) in mature B cells
What are the CD markers on B cells?
What do plasma cell antibody factor contain?
Clock face chromatin
What do memory B cell do?
Allow for quick immune response on re-exposure
Can present antigen
Which surface marker do memory B cells contain
Forms Ca2+ channel
Marker for late stage of a B cell development
What do the lymphoid tissue consist of?
1) capsule (some but some don't have)
A) lymphocytes (B or T)
B) other cells of the immune system: Macrophage and Dendritic cells
3) supporting tissue
A) reticular fibres (type III collagen) mainly produced by reticular cells (fibroblast)
B) thymus is an exception supported by a network of unusual epithelial cells
What is an example of primary lymphoid tissue?
What is bone marrow used for?
Site of lymphocytes progenitor cell
1) B cell
2) T cell (needs thymus for education and maturation)
3) Natural Killer lymphocytes
What are natural killer cells?
Develop from same precursor cell as B and T cells
Ability to kill certain types of target cell
How do NK cells kill target cells
After recognition, they release perforins and granzymes, substances that create channels in the cell's plasma membrane, which induces them to undergo apoptosis
What do macrophages do?
1) Endocytose and partially degrade both protein and polysaccharide antigens before they present them in conjunction with MHC2 molecules to helper CD4+ T lymphocytes
2) They digest pathogenic microoranisms through lysosomal action on combination with the helper CD4+ T lymphocytes
3) They secret multiple cytokines including lymphokines, complement components, and interleukins as well as acid hydrolyses, proteases and lipases
What are lymphatic vessels?
Route by which cells and large molecules pass from the tissue spaces back to the blood
What happens when lymph circulates the lymphatic vessels?
It passes through lymph nodes. Within the lymph noes, antigen conveyed in the lymph are trapped by the follicular dendritic cells. The antigen exposed on the surface of follicular dendritic cells can be processed by APC present in lymph node
What is the difference between the way lymphocytes in blood vs lymph entering lymph node
Lymphocytes conveyed in the lymph enter lymph nodes via afferent lymphatic vessels
whereas lymphocytes conveyed in the blood enter the node through the walls of postcapillary venules (high endothelial venules
How do lymphocytes leave the blood?
Leave via the efferent lymphatic vessels, which lead to the right lymphatic trunk or to the thoracic duct.
Which part of the body has an accumulation of lymphatic nodules with no capsule?
Alimentary canal (GIT)
what are lymphatic nodules with no capsule or free cells of this tissue called?
Mucosa-associated lymphatic tissue (MALT) because of its association with mucous membrane.
Where in the GIT are MALT and what type of MALT are contained?
1) Waldeyer's ring found in Palatine Tonsils, Pharyngeal Tonsils, Lingual tonsils
2) Peyer's Patches in small intestine
3) Scattered single lymphoid cells - mainly B cells and plasma cells in small and large intestines mainly secreting IgA
Name the properties of MALT?
1) Aggregates of lymphoid tissue - up to 70% of total in body
2) No capsule or sinuses
3) Mainly B cells, organised into follicles
4) Close relationship with overlying epithelium
What does MALT do?
Provide immunologic protection on exposed surfaces. (interact and initiate immune response)
After MALT contacts with antigen, what does it do?
travel to regional lymph nodes, where they undergo proliferation and differentiation. Progeny of these cells then return to the lamina propria as effector B and T lymphocytes.
Most nodules are secondary nodules, what distinctive features do they have?
1) Germinal center
2) Mantle zone or corona
Where is the germinal center located in the nodule? What does it look like in histological sections?
In the central region of the nodule and appear lightly stained in histological sections
When does the germinal center develop?
When a lymphocyte that has recognised an antigen returns to a primary nodule and undergoes proliferation.
What does the germinal centre do?
Site of B cell activation in response to antigenic challenge.
What does the germinal center contain?
1) B lymphocytes with admixed TH cells and antigen presenting cells.
2) Scattered macrophage is in active germinal centre
3) lymphocytes that have large amounts of dispersed euchromatin
What happens when antigen is presented to naive or immature B cells in germinal centres?
1) Antigen presented by their antigen presenting cells - called dendritic reticulum cells and with the help of scattered T helper cells
2) Transform and proliferate to produce centroblasts then centrocytes
3) eventually plasma cells and memory cells
What do the macrophage of in an active germinal centre?
Engulf apoptotic cells
What is the mantle zone?
Outer ring of small lymphocytes that encircles the germinal center.
What do tonsils do?
Form a ring of lymphatic tissue at the entrance of the oropharynx.
-partially encapsulated lymphoid tissue
What is tonsils associated with?
associated with mouth and pharynx
What are the different tonsils located at the entrance of the oropharynx?
1) Pharyngeal tonsils (located in the roof of pharynx)
2) Palatine tonsils (located on either side of the pharynx and between the palatopharyngel and palatoglossal arches)
3) Lingual tonsils (base of the tongue all contain aggregates of lymphatic nodules)
What do the palatine tonsils have?
Dense accumulation of lymphatic tissue located in the mucous membrane
What is Peyer's Patches found?
located in the ileum (distal portion of small intestine)
What does Peyer's Patches consist of?
1) Numerous aggregations of lymphatic nodules containing T and B lymphocytes.
2) M cells (microfold cells)
Where is M cells found?
In the follicle associated epithelium of the Peyer's patch
What does the M cell do in Peyer's Patch?
Transport organism and particles from the gut lumen to immune cells across the epithelial barrier thus is important in stimulating muscle immunity
What is GALT?
Gut associated lymphatic tissue in the alimentary canal.
What does MALT refer to?
Both BALT(bronchus associate lymphatic tissue) and GALT
What is Mucosa of GIT rich in?
Lymphocytes - diffuse and in aggregates