Lymphoid tissues Flashcards
Every area of the body can become infected so what does this mean for the immune cells?
- immune cells need to be everywhere and traffic quickly to sites of infection
Different sites of the body require different immune responses - what exists to aid this?
- specific immune tissues to allow for fat, appropriate responses
What is the name for the specific immune tissues?
- lymphatic tissues
What cells does the immune system rely on?
- relies on sentinel cells throughout body tissues
- non- immune cells within tissues
- circulating immune cells
Give examples of sentinel cells:
- DCs
- macrophages
- and others
What do the sentinel cells do?
- these will identify pathogens vis PRRs (recognise PAMPS) and have toll like receptors that can recognise conserved non self
- and take in antigens to then present to adaptive immune cells to help activate T and B lymphocytes
What do non-immune cells within tissues do?
- present antigen from within their cells to patrolling activated adaptive immune cells
- releases cytokines to warn of infection and bring in immune cells to site of infection
If a cell is not infected what will it show and vise versa?
- if a cell is not infected it will show off self proteins
- if a cell is infected it will show non-self proteins and can attract immune cells
What are circulating immune cells?
- innate (neutrophils) and adaptive (T and B cells)
What are circulating innate immune cells important in?
- critical in amplifying response (more cells to respond) and effector response
What does the immune system require to all work together?
- requires specific tissues and circulation
What are the two components of immune system circulation?
- lymph and blood
What is lymph?
- fluid circulating through lymphatic vessels
Where is the lymphatic system found and what is its purpose?
- found throughout the body
- purpose is draining tissues and takes liquids, antigens and, molecules
What does the lymphatic system link?
- links most lymphatic organs
What is the lymphatics system separate from?
- separate vessels from blood circulation but there is movement between them
Describe lymphatic circulation:
- Not closed
- slow /inconsistent speed
- about draining
- has non-immune functions
- tissue fluid filtered
- cleans up debris
What cells are present in lymph circulation?
- various leukocytes present
What are the key roles of the lymphatic system?
- sampling the tissue (debris, antigens etc.)
- maximising the chances of specific lymphocyte activation during an infection - migration, no static cells
When the lymphatic system is sampling what is normal to find?
- self proteins are normal
How can antigens arrive at the lymph node?
- antigens can arrive in the lymph via draining
- or via antigen presenting cells (APCS = macrophage, DCs and B cells)
What happens during a local infection?
what are the responses and actions?
- local infection/penetration of the epithelium
- sentinel cells already in the tissue
- activated by PAMP or damage when they encounter pathogens
- then release cytokine which tells immune cells there is a problem
- cells also migrate through the lymphatic node to where T and B cells are for an adaptive immune response
What are the lymphoid organs in a pig?
- lymph nodes
- spleen
- respiratory tract
- thymus
- salivary gland
- bone marrow
- mammary glands
- intestine
- urogenital tract
What happens in primary lymphoid tissues?
- where lymphocytes are formed and mature
What happens in secondary lymphoid organs?
- where lymphocytes are activated
Name a primary lymphoid organ:
- bone marrow
What happens in the bone marrow (primary lymphoid organ)?
- B cell development and selection
- also development and selection of innate immune cells (neutrophils, monocytes, eosinophils)
- T cell originate here but migrate to thymus for development and selection
Why is selection important?
- because due to the random production of receptors B and T cells could have antibodies to self proteins (not good = autoimmune diseases)
What happens in the thymus?
- T cell development
where is the thymus located?
- cranial to the heart
What is the role of the thymus?
- to screen out potential auto-reactive T cells (that may react to self proteins) before they reach the circulation
What are primary lymphoid tissues in a chicken?
- harder gland
- thymus
- spleen
- caecal tonsils
- bursa of fabricius
- bone marrow
- liver
Where is the site of B cell development in birds?
- Bursa of Fabricius
What are the secondary lymphoid organs?
- lymph node
- spleen
- MALT
What are lymph nodes?
- crossroads where cells/antigen can meet and leads to activation of lymphocytes
What drains into the lymph nodes?
- blood containing lymphocytes
- lymph containing antigens and APCs migrating to lymph node
Where does lymph drain from?
- drains to lymph nodes from the local tissue
Why do we sample lymph nodes?
- to see if an infection have moved out of the local tissues
Name the lymph nodes? - also look at diagram and match them!
- submandibular
- parotid
- rectopharynheal
- prescapular
- axillary
- bronchial
- mesenteric
- superficial inguinal
- popliteal
Leukocyte circulation through the lymph nodes means that antigen and antigen-bearing cells move from what to where and how?
- antigen and antigen bearing cells move from local tissues via afferent lymphatic vessels
What does afferent mean?
- vessels leading into
During leukocyte circulation through lymph nodes naïve lymphocytes continually re-circulate - how do they do this?
- enter lymph node from the blood and leave via efferent lymphatic vessels
What are naïve lymphocytes?
- non-activated lymphocytes
What does efferent mean?
- vessels leading away
Lymph nodes are a highly organised environment evolved for what?
- activation of lymphocytes
- proliferation (more recognising cells are being replicated)
- differentiation of lymphocytes become specialised
What happens in the lymph nodes?
- APC s (antigen presenting cells) present antigen and active T-cells and B cells
- activated T-cells interact with and activate B-cells
- Germinal centres form (proliferating B cells, generating high affinity antibodies)
What do most B cells require to activate them?
- T cells
What is found in the primary lymphoid follicle of a lymph node?
- mostly B cells
What is found in the medullary cords of a lymph node?
- macrophages and plasma cells
What is found in the paracortical area of a lymph node?
- mostly T cells
Describe the process of cells getting to a lymph node and what happens within the node:
- immature dendritic cells reside in peripheral tissues
- dendritic cells migrate via lymphatic vessels to regional lymph nodes
- mature dendritic cells activate naïve T cells in lymphoid organs such as lymph nodes
- antigen-receptor binding and co-stimulation of T cell by dendritic cell leads to proliferation and differentiation of T cell to acquire effector function
- antigen-receptor binding and activation of B cell by T cell leads to proliferation and differentiation of B cell to acquire effector function
Why should superficial lymph nodes be palpated in a clinical exam?
- because of role in active immune response
What is the name for enlarged lymph nodes?
- lymphadenopathy
What could lymphadenopathy be a sign of?
- infection or neoplasia
What things can be used to investigate the lymph nodes?
- cytology of the lymph node
- lymph node aspirates can be take
What can you look at from a lymph node aspirate?
- cell type = useful for identifying whether cancer is present
- cell morphology
- pathogen presence
What do birds and reptiles lack?
- lack lymph nodes
What do birds and reptiles have instead of lymph nodes?
- contain lymphoid nodules = not as organised
What do ducks have?
- structures closer to mammalian lymph nodes
What is the structure of a pigs lymph nodes?
- they are inverted
The spleen is a big lymph node but deals only with what?
- blood
Where is the spleen located?
- left cranial quadrant of the abdomen
- near the end of the rib cage in dogs
The amount of spleen below the ribcage varies based on what?
- contraction/congestion
The spleen is divided into what and what are the functions of these divisions?
- red pulp = haematological functions
- white pulp = immunological functions
How where the divisions of the spleen named?
- named based in role (red blood cells vs white cells) and visual appearance
(even though white pulp looks darker than white)
What does red pulp of the spleen do?
- non-immune function
- removal of particulate material from bloodstream
- destruction of old RBCs
- storage of red blood cells and platelets 20-30%
What is the role of white pulp in the spleen?
- similar role to lymph node BUT spleen filters microbes, antigens and antigen-antibody complexes from BLOOD ONLY
- mature DCs and macrophages migrate from tissues to the spleen via blood
- reside in marginal zones
- allows activatory interactions with lymphocytes
What is MALT
- Mucosa Associated Lymphoid Tissues
What does MALT include?
- Gut associated lymphoid tissues (GALT)
- nasal associated lymphoid tissues (NALT)
- Bronchus associated lymphoid tissues (BALT)
What do MALT have to deal with a lot of?
- a lot of non-self antigens
MALT have a different environment why?
- due to commensals, environmental antigens (food etc.), mucus
Where does most exposure to pathogens occur?
- occurs at mucosal surfaces
MALT have more …. compared to the rest of the body
- more lymphocytes
What type of lymphocytes does MALT have?
- specialised lymphocytes with special rules of re-circulation
What cells do GALT contain?
- Peyer’s patches
Where are Peyer’s patches found?
- in small intestine, mostly in the ileum and at the ileocecal junction
Peyer’s patches are covered by an epithelial layer containing specialised cells called what?
- M cells
What are M cells?
- specialised antigen-sampling cells at the surface of Peyer’s patches which have characteristic membrane ruffles
Peyer’s patches have a dome beneath containing what? and what happens here?
- DCs and macrophages
- some T-cells
- B-cells
- migration happens due to efferent lymphatics
What also happens in Peyer’s patches?
- regulation as you don’t want ton respond to food antigens even if they are non-self and need to be able to tolerise certain antigens
What is the function of Peyer’s patches in the immune system?
- activation of lymphocytes
- germinal centre formation
- prevention of inappropriate activation
What can inappropriate activation lead to?
- food allergies
- inflammatory bowl disease
Food allergies and inflammatory bowl disease are immune-mediated which means what?
- they result from a break down in regulation in GALT
What are cytokines critical in?
- inflammation and regulation
