Lecture 25 Flashcards
What is the function of the Lymphatic system?
- Monitor body surfaces and internal fluid compartments
- remove excess interstitial fluids
- provide a defense mechanism
- produce immune cells
- fatty acid absorption and transport of fat, chyle to general circulation.
What are the primary organs of the lymphatic system?
Bone marrow and thymus GALT
what are the secondary organs of the lymphatic system?
(stlylyd)
Spleen, tonsils, lymph nodes, diffuse lymphatic tissue, lymphatic nodules
What are the principal effector cells of the lymphoid system?
Lymphocytes: B cells, T cells, Natural killer cells
What are the support cells of the lymphatic system?
monocytes, macrophages “Phils”, neutrophils, basophils, eosinophils, dendritic cells, follicular dendritic cells
what are the specialized epithelial stromal cells of the lymphatic system?
reticular cells, langerhans, epithelioreticular cells
What cells are responsible for immunological surveillance?
Lymphocytes
What is referred to as the faith of lymphocyte cells 60% versus 30%?
-(60%)mainly long lived mature T-cells, circulating pool of immunocompetent cells
(30%)- short lived immature or activated but destined for specific tissue ( CT, epithelia)
Where are T-lymphocytes differentiated? what kind of immunity do they do?
In the thymus, cell mediated immunity
T-lymphocytes secrete cytokines when activated, what do they affect the function of and what cytokines are expressed?
T cell receptors recognize what kind of molecules?
effector cells and
Express CD2, CD3, CD5, CD7, CD28, CD 40L.
MHC molecules
What are the subclasses of T lymphocytes?
T helper cells and Cytotoxic lymphocytes
what is the difference between T helper cells and Cytotoxic lymphocytes?
T-helper cells: Th1,Th2= recognize antigens presented by antigen presenting cells APCs and express CD4
Cytotoxic lymphocytes (CTL/patrols)- express CD8 and recognize antigens present on cancer or viral infected cells.
How are TH cells activated?
1- First signal is when they interact with MCH-Ag complex
2- Costimulatory signal between the T cell and APC
- Synthesize interleukins (CD4 cytokines which stimulate differentiation and proliferation of T,B and NK cells)
How do TH1 cells work?
They recognize Ag presented by APCs
synthesize-IL2, IFN-y, TNF-a-
Interact with cytotoxic lymphocytes, cells and macrophages to control intracellular pathogens.
How do TH2 cells work?
Recognize Ag presented by APCs
Synthesize IL4,IL5,IL10,IL13
Interact with B lymphocytes to initiate antibody mediated immune response for extracellular pathogens
What are regulator (suppressor) T-lymphocytes?
Suppress the immune foreign antigens by influencing other cells:
- CD4+ cells that co-express CD25 and FOXP3+
- Secrete IL10, TGF-B
- delayed hypersensitivity reaction (type 4)
What are gamma/delta T lymphocytes?
develop in thymus/ reside and form first line of defense in epithelia
- another kind is mucosa invariant T-lymohocytes (MAIT)
Natural killer lymphocytes have what kind of immunity?
innate immunity
What enzymes are released by Natural Killer cells?
granzymes and perforins
what CD markers are found in Natural Killer cells?
CD16, CD56, CD94
What kind of receptors are expressed on natural killer cells?
Fc receptors, recognize the Fc region antibodies coating target cells.
What kinds of antibodies coat Natural killer associated lysis?
IgG or complement protein C3- antibody dependent cell-mediated cytotoxicity (ADCC)
Where do B lymphocytes differentiate?
bursa equivalanet organs
what kind of immunity do B lymphocytes participate in?
humoral immunity
what do B lymphocytes express?
antigen binding, B cell receptors, and MHC II on their surface.
What CD markers are found on B lymphocytes?
CD9,CD19,CD20,CD40
What are the subtype of B lymphocytes?
plasma cells and memory B cells
what do plasma cells and Memory B cells do ?
Plasma cells: production and secretion of antibodies IG
Memory B cells: respond to second encounter with the same antigen
How are B lymphocytes activated?
1- first signal when they interact with antigen BCR-Ag complex
- Antigen is engulfed by B cell
- Antigen antibody (Ag-Ab) complex is eliminated by NK cell destruction, phagocytosis by macrophages or eosinophils.
2- costimulatory signal, between the B cell and the TCR on the TH cell..
- T cell secretes cytokines to stimulate B cell differentiation and proliferation
Which antigen presenting cells are part of the Mononuclear Phagocytic System?
-Perisinusoidal macrophages ( Kupffer cells)
- Langerhans cells (skin)
-Dendritic cells ( spleen, lymph nodes)
- Macrophages
( Miami-Dade PoLice)
Which antigen presenting cells are part of the Non-mononuclear Phagocytic system?
-B lymphocytes
-Epithelioreticular cells ( thymus)
-Epithelioreticular cells (II,III)
(BEE)
What is the purpose of macrophages as antigen presenting cells?
- they present antigens to T and B cells, they -partially degrade both proteins and polysaccharides
- digest pathogenic microorganisms through lysosomal action in combination with CD4+ lymphocytes
- Secrete multiple cytokines (lymphokines, complement components, interleukins)
- Sequestration and removal of foreign materials and organisms that remain undigested or have not provoked an immune response
What is a Macrophage I (M1)? what activates it?
activated by IFN-y
avidly phagocytic-lyse ingested pathogens and foreign antibodies
-promote inflammation, ECM damage and apoptosis
What is a macrophage 2 (M2)?
- activated by interleukins
- down regulate inflammation
- promotes rebuilding of ECM and cellular proliferation
- stimulates angiogenesis
Endogenous antigen
- Antigen proteosomal degradation
- Formation of Ag-MHC 1 complex (rEr)
- Translocation of complex via Golgi
- Presentation of Ag-MHC I on plasma membrane followed by CD8 recognition
Exogenous antigen
- MHC II assembly in rER
- Translocation of MHC II to membrane
- MHC II displayed on cell surface
- Endosomal endocytosis of MHC II
- Exogenous Ag endocytosis
- Proteolytic degradation of Ag
- Formation of Ag-MHCII complex
- Display of Ag-MHC II complex on cell surface followed by CD4 T helper recognition
- Lysosomal degradation of failed of Ag-MHC II recognition.
what is innate immunity?
AKA nonspecific immunity:
- occurs through actin of neutrophils, macrophages, mast cells, and NK cells.
- Fast and non-specific
- Does not produce memory cells.
What is adaptive response
AKA specific immunity
- Depends on initial recognition of antigens by B and T cells
- Slower and specific
- Produces memory cells
- Primary and secondary response.
What is antibody mediated immunity?
Helper T-cells and B cells and Plasma cells
- Cause a release of antibodies that act on invading antigen
What is Cell mediated immunity?
- Specific T cells that specialize in cytotoxicity
- Granzymes and perforins
What is diffuse lymphatic tissue ( see histo pic)?
- non encapsulated accumulations of lymphocytes and other free cells ( plasma cells, eosinophils, fibroblasts)
- protects the body from antigens
- initial immune response
- located In lamina propria ( sub epithelial tissue )
- Mucosa Associated Lymphatic tissue ( BALT, GALT)
What cells can you find in a lymphatic nodule and what do they contain?
Lymphocytes:
- B lymphocytes
- activated- proliferate- plasma cells and memory cells
Reticular cells:
-Produce reticular fibers ( stroma)
Dendritic follicular cells:
- Most efficient APCs
- Present antigens on MHC I and II molecules
Macrophages:
Phagocytic and APC ( contain MHC I and II molecules)
Follicular dendritic cells:
-Dendritic and lack MHC II molecules: harbors Ag-Ab complex
What is a lymphatic nodule? where are they located ? what is the difference between a non-encapsulated versus agregated lymph node?
- localized concentrations of lymphocytes and other free cells ( plasma cells, eosinophils, fibroblasts)
- located in the wall of the GI tract ( tonsils, ileum), Respiratory, genitourinary
- non encapsulated, solitary (duodenum) or aggregated ( tonsils, Peyer’s patches)
- protects body from antigens
- Mucosa associated lymphatic tissue (BALT GALT)
What is the difference between primary lymphoid tissue and secondary?
primary: mainly small lymphocytes, dense heterochromatin ( babies)
secondary: after exposure to antigen ( adults)
what are germinal centers found in secondary lymphoid tissue?
- center of lymphocyte activation proliferation and differentiation.
- pale staining central region
- large immature lymphocytes with dispersed heterochromatin
- follicular dendritic cells and macrophages
what is a mantle zone or corona in secondary lymphoid tissue?
outer dark staining region with smaller cells.
Where is the thymus located and what innervation does it lack?
superior mediastinum and it has no afferent lymphatics
what is the origin of the thymus?
3rd pharyngeal pouch
what kind of lymph organ is the thymus ?
lymphoepithelial organ; it contains epithelial reticular cells
Describe what the thymus looks like
covered by a thin CT capsule
Trabeculae run within to divide the tissue as lobules
each lobule has a cortical cap over portions of highly convoluted but continuous inner medullary tissue
It has a cortex and medulla
LOOK AT PIC
What does the thymus cortex contain?
mainly immature T lymphocytes (thymocytes) and ERCs ( epithelial reticular cells)
- thymic epithelial reticular cells are the primary support cells in the cortex
- has more ERC giving more eosinophilic appearance
LOOK AT PIC ( cortex is darker part)
What does the thymus medulla contain?
mature T lymphocytes and ERCs ( epithelial reticular cells
lymphocytes are less concentrated here
Here you will find THYMIC CORPUSCLES within
LOOK AT PIC
what holds together the cytoreticulum in the thymus?
desmosomes
How do blood vessels and blood work in the thymus? what is the direction of the blood supply? what kind of capillary?
blood vessels in the cortex are ensheathed by ERCs ( epithelial reticular cells)
developing T cells are sequestered from blood borne antigens
Blood supply: Enter through trabeculae into the cortex and medulla, contains a continuous capillary
Where is the blood thymus barrier found?
in the cortex
Describe the components of the thymic medulla. what cells are exclusive to the thymic medulla?
- blood vessels in the medulla lose ERC covering,
- Lymphocyte differentiate and enlarge
- Mature T cells migrate into medullary blood vessels and efferent lymphatics
- ERCs contract into spherical, degenerative masses- Hassall’s corpuscle
- Hassall’s corpuscle are only found in the thymic medulla
where are hassle’s corpuscle’s found?
only in the thymic medulla and they have rings of degenerating epithelial reticular cells.
What is the job of a lymph node?
kidney or bean shaped organs of variable size
distributed along the course of lymphatic vessels
they filter lymphatic fluid as it passes through them
Mounts immune response by recirculation of lymphocytes
What are the parts of a lymph node and what do they contain?
what is contained in the capsule, outer cortex, inner cortex, medulla, hilum?
Capsule: dense connective tissue, pierced by afferent lymphatics/ surrounds the node
outer cortex: collection of lymphocytes-prominent nodules ( a lot of b lymphocytes)
inner cortex/paracortex: area between outer cortex and medulla
- collection of lymphocytes
- abundance of T lymphocytes
- no nodules
Medulla: cords and sinuses
at the sinus lymph slows so that
macrophages can attack intruders
Hilum: blood vessels and nerves, lymphatics exit.
LOOK AT PIC
What is the flow of lymph in the lymph node?
afferent lymphatic vessels»»> Subcapsular ( cortical sinus)»»» Trabecular sinus»»> Medullary sinus»» efferent lymphatic vessel
A subway tried mending everything
What is contained in the stroma of lymph nodes? what kind of collagen is found here?
1: reticular cells ( modified fibroblasts) cytoplasmic extensions cover reticular fibers Type 3 collagen
2. Framework for myeloid organs: bone marrow, lymph nodes, and spleen
LOOK AT PIC
remember that reticular fibers are seen with silver stain
What is in the outer cortex of lymph nodes?
area between the capsule and the medulla
characterized by presence of lymphatic nodules
primary and secondary nodules
mainly consisting of B lymphocytes
Presence of few T lymphocytes, macrophages, reticular cells, and APCs
LOOK AT PIC.
What characterizes the paracortex/ deep/inner cortex of lymph nodes?
Area between outer cortex and medulla
primarily has T lymphocytes
characterized by the presence of high endothelial venules (HEV) (LOOK AT PIC)
What is the purpose of HEV high endothelial vessels found in the paracortex/ deep endothelial vessels of a lymph node?
allow for the transition of lymphocytes from the blood stream to lymph tissue within lymph node
What can you find in the medulla of a lymph node?
cords and sinuses
what is a cord in medulla of a lymph node?
branched cord-like extensions of dense lymphoid tissue
contain primarily B lymphocytes, plasma cells,, reticular cells and macrophages
LOOK AT PIC
What is a sinus in lymph node?
- dilated spaces separating medullary cords
- contain lymph, few wandering macrophages
- granulocytes maybe present when lymph node is draining an infected region.
LOOK AT PIC
