Immune System: Anatomy & Function Flashcards
What is the positive and negative of the mobility in lymphoid cells?
positive: if have infection in one part of the body, lymphocytes have ability to mobilize & see if are other areas of infection ion the body
negative: if have autoimmune disease against specific antigen, the immune system can find all those sites in the body & cause havoc
why is the heart one of the most important organs?
-because it pumps lymphocytes through the blood
what are the two types of cells in lymphoid tissues?
1) migratory cells (transient)
2) resident stroll cells
* immune response depends on interactions between them*
migratory cells
- in lymphoid tissues
- consist of T & B lymphocytes, dendritic cells, macrophages & differentiated plasma cells
- granulocytes, erythrocytes
lymphoid tissues
-means tissue with many lymphocytes
granulocytes
- bone marrow derived migratory cells in lymphoid tissue
1) neutrophils
2) basophils
3) eosinophils
what are some of the resident stroll cells?
1) epithelial cell populations (thymic epithelium & follicle epithelium)
2) mesenchyme derived
3) connective tissue, smooth muscle, forming capsule & other structures
4) blood supply (endothelium, pericytes)
thymic epithelium function
- a resident stromal cell
- assit in T lymphocyte repertoire selection
follicle epithelium
- a resident stromal cell
- in mucosal lymphoid tissues
- assists in immune surveillance
mesenchyme derived stromal cells?
- resident stromal cells
- provide structural support and cytokines
what does the stromal do?
- is way station for migratory cell populations
1) help provide environment for education of lymphocytes
2) involved in organization of the lymphocytes
3) help lymphocytes know who they need to be communicating with
the bone marrow?
-where most of hematopoiesis takes place
hematopoiesis in adults vs babies?
- process of producing new blood cells
- in adults occurs in bone marrow
- during early develop begins in the yolk sac (early) & fetal liver (later)
- in adults can occur in spleen, but rare unless have pathological conditions which effect bone marrow
what does early fetal liver resemble? why?
-resembles bone marrow since undergoing hematopoiesis (Stem cells differencing into different blood cells)
bone marrow structure?
- has matrix of bone, fat (adipocytes) , and blood vessels
- has diverse cells types, clusteres of myeloid (neutrophil, macrophages) & RBC
How do the hematopoietic stem cells differentiate?
- is not one hematopoietic stem cells that creates many different types of cells
- typically one stem cell makes one type of cell (RBC vs. neutrophil etc)
- end up with clusters where mainly one type of cell is being generated
Megakaryocytes
- specialized bone marrow cells also found in spleen
- multi-nucleated large cells
- produce platelets
Where do plasma cells take up residence?
- differentiated plasma cells working as antibody factories often return to the bone marrow and release abs from there
- are also in many other tissues
primary lymphoid tissue?
- Thymus, Bone Marrow, Spleen (sorta)
- sites of hematopoiese & lymphocyte production/maturation
why is thymus a primary lymphoid tissue?
-even though T cells are made in the bone marrow, they mature in the thymus making it a primary lymphoid tissue
secondary lymphoid tissue?
-where adaptive immune responses are induced by association of lymphocytes & myeloid cells
-lymph nodes, tonsils, spleen
-
1) myeloid cells
2) lymphoid cells
1) include monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, and megakaryocytes to platelets
2) T cells, B cells, and natural killer cells
- dendrites can be derived from BOTH*
why is spleen a secondary lymphoid tissue?
- immune responses immune responses can originate in the spleen
- but can also have some primary functions since is capable of mild hematopoiesis w/ hematopoietic stem cells
tertiary lymphoid tissue?
- lymphoid accumulations organize into this type of tissue at sites of chronic immune responses
- accumulations eventually start to look like secondary tissue, is why considered lymphoid tissue
- doesnt occur normally in peripheral tissues; only occur in chronic immune response
T lymphocytes progression to maturity?
1) start as Common Lymphocyte Progenitor (CLP) in bone marrow
2) migrate into thymus causes induction of development program for t-cells
3)
Common Lymphocyte Progenitor (CLP)?
- made from the bone marrow
- both B andT cells & NK cells are made as this first, then differentiate
the thymus and maturing T cells?
- has two compartments that define T lymphocyte development stages
- two compartments come from the high nucleic acid content & densely packed lymphocytes
What are the two compartments of the thymus
1) cortex
2) medulla
cortex
- densley packed immature thymocytes undergoing positive selection of the receptor repertoire capable of recognizing self-MHC
- positively select T-cells that can respond to MHC class I and II
medulla
- less densely packed compartment w/ many dendritic cells that assist in negative selection (deletion) of developing T-cells with self-reactive receptors
- these T cells bind to self antigens from the periphery
thymus and age?
- as get older thymus undergoes involution
- T cell output decreases (never stops entirely)
- leads to larger medullary compartment & more connective tissue (more fibrotic though)
why is medulla less dense?
-because contains more myeloid (dendritic) cells to destroy self-loving T cells
How tell human thymus vs mouse thymus?
- Hassalls corpuscles
positive selection (MHC restriction)?
- cortical epithelium in thymus expresses MHC I and II molecules to select receptors with general self- MHC binding
- if bind too well indicates could cause auto-immune rxt, needs to be destroyed
negative selection ?
- deletion of auto reactive T-cell
- in medulla
- medullary dendritic & epithelial cells present intrinsic self antigens for negative selection
- dendrites & medullary epithelium also have peripheral antigens to help find autoreactie T cells
peripheral antigens?
- dendritic cells migrate to medulla from periphery to present self peripheral antigens -medullary epithelium express peripheral antigens through promiscuous gene trxn
- both help negatively select against auto reactive T cells
how do multi-organ autoimmune rxt occur?
- when lacking the negative selection and promiscuous gene expression of the medullary epithelium
do most lymphocytes produce successful receptors?
- no; lymphocyte receptors are pieced together to form the final product
- often they can’t recognize MHC I or II and therefore require positive selection
the spleen
- accumulate functional cells that have been exported from thymus
- is filter, block anti-bodies bound to antigens from circulating in blood
- has two main compartments
1) white pulp= lymphoid
2) red pulp= myeloid
what do the white and red pulp of the spleen refer to?
- refer to appearance of freshly cut tissue
red pulp
- provides a reservoir of red cells (which is why is has such a iron mineral taste); macrophages, megakaryocytic in some species stress response can rapidly mobilize into blood
the spleen and stress?
-in some species have fibrous material in red pulp, when undergo stress fibrous bands of smooth muscle constant and push RBC into circulation
white pulp
- like a lymphoid organ (secondary lymphoid tissue)
- part of arterial circulation, empties directly into the parenchyma of the spleen
- organize T & B lymph & myeloid cells w/ stromal cells to make sure are engaged to produce immune response
lymphocytes and white pulp?
-lymphocytes can migrate directly to their respective regions of the white pulp w/o requiring extravasation or homing receptors
red pulp sinusoids?
- provide a filtering function for blood
- it can accumulate pigments from old/degraded RBC
which is more promient red or white pulp?
-white pulp less prominent than red
what is white pulp characterized by?
-clear accumulations of lymphocytes
white pulp structure?
1) central arterial surrounded by lymphocytes (mainly T)= peri- Arteriolar Lymphatic Sheath (PALS)
2) B cell follicles & Germinal centers found next to PALS, clearly connected, but are distinct zones
Lymphoid tissue structure?
- can have slight variations but generally similar to that of white pulp
- have clear distinction between B cell follicle and Germinal centers that are around a central arterial
- Germinal centers are where adaptive responses original
lymphatics what do they do and structure?
- is a way lymphoid organs can communicate
- lymphatics drain the peripheral tissue & provide flow of immune cells into draining lymph nodes
- vessel walls very thin, usually empty except when filled with inflammatory cells in active infection
Where are lymphatics in body?
- run w/ arteries and veins but are distinct
- have very thin endothelial wall separating them
- hard to find, often look like gaps in connective tissue
Lymphatics and adaptive immune response?
- lymphatics help antigen presenting cells survey tissue & move quickly from tissue tho lymph nodes by lymphatics
- lymph node where adaptive immune response is activated
what are two ways cells can get into lymph nodes?
1) lymphatic afferents
2) post capillary venules
Lymphatic afferents and the lymph nodes?
- in active infection, get swelling & inflammation in peripheral tissue
- draining from tissues into lymphatics takes the dendritic cells & macrophages to lymph node
- can activate adaptive immune response
post capillary venules
and lymph nodes
-lymph nodes have regular blood supply, so dendritic cells & macrophages (antigen presenting cels) can get into the lymph nodes through capillary venules
Lymph node structure?
1) lymph nodes have a clearly defined connective tissue capsule
2) folliclar dendritic cells
3) mesenchymal stromal cells
where do lymphatics drain into?
-drain into the sub capsular cortex
mesenchymal stromal cells in lymph node?
-cells provide support for tissue and produce chemokines to guide B & T cells to their place in lymph node
does lymph node blood supply?
-yes has a blood supply including post-capillary venules that deposit lymphocytes into the node
stromal cell role in lymph node?
- provides structrue so lymphocytes/ myeloid cells can sort themselves out
- provide scaffolding to make sure cells to right place
endothelial cells of post capillary venules (PCV)
- cuboidal, not squamous (flat)
- referred to as High Endothelial Venules (HEV)
High Endothelial Venules (HEV)
-express adhesion molecules that help lymphocytes stick, migrate and then extravasate (break through) to enter lymph nodes
what is the composition of lymph nodes?
- densely packed w/ lymphocytes
- have B cell follicles & Germinal centers when active
- in between follicles (interfolliclar spaces) are a mixture of T lymphocytes & dendritic cells
Germinal centers
- sites within secondary lymphoid organs (lymph nodes & spleen)
- where mature B cells proliferate & differentiate
medullary cords in lymph nodes?
- lymphocytes are relatively sparse but plasma cells (make antibodies) & macrophages are more abundant
lymph node distribution of T and B lymphocytes?
-like the spleen, lymph nodes have segregation of B & T
Where are T cells in lymph nodes?
-the interfollicular zones, associated w/ dendritic cells
where are the B cells in lymph nodes?
-in the follicles, have Germinal centers where they are produced
Lympho-Stromal interactions? (X2)
- help move B and T cells to their correct locations; compartmentalization
1) stromal cells in the follicles produce CXCL13 to attract B cells (& some helper T cells)
2) storm cells in the inter-folicle regions produce CCL21 to attract native T cells & dendritic cells
what are CXCL13 and CCL21?
-chemoattractants peptides specific for B and T cells respectively
Benefit of dendritic cells and T cells responded to same chemoattractant?
- forces their interaction; which is what needs to happen to activate the adapted immune response
- T cells need to see antigen presented on dendritic cells
mucosal lymphoid tissue?
- ~ 70% of immune system is in mucosal tissues
-tissues are critical barriers maintain the host-microbial relationship
-
mucosal tissue examples?
- airways (lungs)
- intestine
- first line of defense against outside pathogens, need to be able to protect but also send those antigen to immune system to fight (immune surveillance)
mucosal tissue consist of?
- mucosal tissues have many types of organized lymphoid tissues (tonsils, very organized tissue)
- allows the organization and ability to have immune response, while providing protective barrier from outside pathogens
upper airway example?
- have tonsils ( highly organized) covered by stratified squamous epithelium
- antigen uptake by M cells in the crypt epithelium, not by afferent lymphatics
intestinal organized lymph tissue?
- intestine includes appendix, Peter’s patches and isolated lymphoid follicles (ILF)
- unlike lymph nodes there are no afferent lymphatics, antegen is taken up by follicle epithelium M cells at lumen
Why epithelial M cells and not afferent lymphatics?
- mucosal lymphoid tissue requires barriers/screening from external antigens, not internal, so the surveillance needs to be oriented toward lumen of gut/respiratory track
- M cells in epithelial point outward toward lumen of these areas
is there organization in mucosal lymphoid tissue?
-yes, have the similar organization of B cell follicles w/ germinal centers with T cells & dendrites in-between follicles (indicates can activate immune response)
airways and mucosal lymphoid tissue?
- can be diffuse accumulations and organized Bronchus-Associated Lymphoid Tissue (BALT)
omentum and mucosal lymphoid tissue?
- omentum= caul fat
- has lymphoid aggregates called Milky Spots
caul fat
fatty membranous tissue in the peritoneum, attached to lower margins of the stomach
intestine and mucosal lymphoid tissue?
-small aggregates called crypto patches, can grow to become Isolated Lymphoid Follicles (ILF)
chronic inflammation and mucosal lymphoid tissue?
-can cause accumulations of cells including lymphocytes and eosinophils
M cells
- mucosal epithelium is a barrier o entry but in mucosal lymphoid tissue (tonsils, Peyer’s patch, BALT) specialized M cells sample lumen contents
- lack brush border microvilli, have basolateral pocket B lymphocyte
- have dendritic & T cells in sub epithelial zone to present antigen & induce mucosal immune response
