Lymphoid Flashcards
0
Q
What makes up the encapsulated lymph organs?
A
Lymph nodes, thymus, spleen
1
Q
Functions of the lymphatic system
A
Defence/immune response
Maintenance of body fluids
Extramedullary hematopoiesis
2
Q
What is the diffuse lymphoid system?
A
Not encapsulated parts of the lymphoid system
3
Q
The lymphoid system does what?
A
Protects the body against foreign macromolecules, virus, bacteria, and other invasive micro-organisms, also kill virally transformed cells
4
Q
Three types of body defence
A
Epithelial barriers
Innate immune system - macrophages, neutrophils, NK cells, complement
Adaptive immune system - T and B lymphocytes, antigen presenting cells (APC)
5
Q
Function of lymphatic vessels
A
Collect excess interstitial fluid from cells/tissues and returns it to the cardiovascular system/general circulation
Moves lymph through lymph nodes
6
Q
Describe the flow in lymphatic vessels
A
Passive fluid flow, no pressure
Valves to control back flow
7
Q
Tissue deposits lymph into….
A
Lymphatic capillaries to the lymphatic vessels to the lymphatic ducts and then into the great veins of the neck
8
Q
The smaller of the lymph ducts does?
A
Collects lymph from the upper right quadrant of the body and dumps into the right lymphatic duct and into the subclavian
9
Q
The larger of the lymphatic ducts does?
A
Begins in the abdomen and ascends through the thorax/neck collects lymph from the remainder of the body then to the thoracic duct and then to the subclavian
10
Q
Describe lymphatic vessels (compare to blood vessels)
A
Thinner walls, single layer of attenuated endothelial cells with an incomplete basal lamina, more valves, contains lymph, unfenestrated
Blood vessels are thicker walls with three tunicas, contains blood, fenestrated/unfenestrated
11
Q
What is lymphedema (elephantitis)?
A
Blockage of lymph flow resulting in a build up of lymph fluid. Either inherited (primary) or caused by injury/disease of lymph vessels (secondary)
12
Q
What is filariasis?
A
Tropical parasite infection that is common cause of secondary lymphedema when nematodes colonize the lymphatic system
13
Q
What is cellulitis?
A
Inflammation/infection of the lymphatic system
14
Q
T or F: Lymphedema can develop months-years post therapy in cancer patients
A
T
15
Q
What is the treatment of lymphadema?
A
Varies on severity and degree of fibrosis includes compression and gradient pumps
16
Q
What is lymphangitis?
A
Lymph vessel inflammation commonly seen with strep infection. Bacteria enter through ann injury and enter lymphatic system and multiply rapidly and spread. The infected vessels become inflamed causing red streaks below the skin surface. Growth is so rapid that immune system doesn’t respond fast enough.
17
Q
Complications of lymphangitis
A
Abscess formation, cellulitis (generalized infection of the lower skin layers) or septicemia (blood poisoning). Can be secondary to malignancy like breast, lung, stomach, pancreas, and prostate cancers.
18
Q
Who is most at risk for developing lymphangitis?
A
Radical mastectomy, leg vein removal for coronary bypass, recurrent lymphangitis caused by tinea pedis (fungal foot infection)
19
Q
T or F: Lymphatic vessels are commonly used for cancer metastasis
A
T
20
Q
What composes the innate immune system?
A
NK cells, neutrophils
Macrophages - differentiate in connective tissues like the histiocytes, macrophages kupffer cells, langerhans cells, or microglia
Mediate phagocytosis and present the antigen to lymhocytes
21
Q
What composes the adaptive immune system
A
B cells - generated and differentiate in the bone marrow bursa,, produce antibody and participate in humoral immune response, plasma cells and memory B cells
T cells - generated in the bone marrow, differentiate in the thymus. Participate in cell-mediated immune response, cytotoxic, helper, suppressor, and memory T cells
22
Q
List the nonspecific contributors to the innate immune system
A
Complement - a system of blood-borne macromolecules known as:
Macrophages and neutrophils - phagocytose invaders
Natural killer cells - kill tumor cells, virally infected cells, bacteria, and parasites
23
Q
Describe the basic functions of the adaptive immune system
A
Reacts to a SPECIFIC antigentic component of the pathogen
Ability to react against that component improves with each subsequent confrontation
24
What are the four distinctive adaptive immune response properties?
Specificity
Diversity
Memory
Self/Non self recognition
25
What cells contribute to the adaptive immune system response?
T lymphocytes
B lymphocytes
Antigen presenting cells (APC)
26
How do adaptive immune response cells communicate?
Signaling molecules known as cytokines which are released in response to encounters with foreign antigens
27
Humoral immunity is mediated by?
Antibodies
28
What is Ig-A?
Secretory antibody in tears, saliva, gut, nasal
29
Structure of antibody?
Two heavy chains connected with disulfide bonds, two light chains attached to heavy chain by disulfide bonds. Variable regions on both chains
30
What is Ig-D?
Activates B cells
31
What is Ig-E?
Degranulates mast cells and basophils
32
What is Ig-G?
Opsonin, NK cytotoxicity (most common)
33
What is Ig-M?
1st isotype formed in the primary response
34
Lymphoid immune cells participate in:
Eliminating non-self organisms, eliminating cancerous cells (surveillance theory), rejection of implants/transplants, autoimmune diseases, lymphoma (cancer of lymphoid tissue)
35
What factors weaken the immune response mediated by lymphoid immune cells?
Cancer treatment, AIDS, stress
36
Function of the primary lymphoid organs?
Responsible for the development and maturation of lymphocytes into mature immunocompetent cells
37
Examples of primary lymphoid organs? Function?
Thymus - T cells mature here
Pre/postnatal bone marrow - B cells mature here in the bursa
Fetal liver
38
What are secondary lymphoid organs?
Mature distribution of lymphoid cells. Responsible for the appropriate environment for immunocompetent cells to interact with each other, antigens, and with other cells to mount an immune response to invading pathogens
39
Examples of secondary lymphoid organs
Lymph nodes, spleen, mucosal associated lymphoid tissues (MALT) postnatal bone marrow
40
Two categories of lymphatic organs (structural). Examples?
Encapsulated (dense) - bound by connective tissue capsules like the thymus, spleen, lymph nodes
Unecapsulated (diffuse) - MALT, BALT, GALT, tonsils
41
What is the thymus?
Primary lymphoid organ
Site of T cell maturation
Located in the superior mediastinum and extending over the vessels of the heart
42
Functions of the thymus?
Responsible for immunological competence of T cells
| Elimination of self-reactive T cells (establishing and maintaing self-tolerance)
43
Structure of the thymus
Lobes and lobules
2 lobes that arise separately during embryonic development
lobules are formed by incomplete divisions of lobes and formed by septa (trabeculae) extending into the lobes from the dense collagenous connective tissue of the thymus capsule
44
What are thymocytes?
Immature immuno-incompetent T cells that migrate from the bone marrow.
Leave the vasculature at the corticomedullary junction and migrate to the periphery of the cortex - moving deeper with maturation
45
Thymocytes migrate into the...
Cortex
46
What does the thymus cortex contain?
macrophages, APCs, and epithelial reticular cells
47
What happens to the thymocytes once in the cortex of the thymus?
```
They proliferate (cortex stains DARK, lots of thymocytes)
They mature and are instructed.
```
48
What color does the cortex stain?
Dark due to lots of thymocytes present
49
What is the blood thymus barrier?
Present ONLY in the cortex and is essential for the thymocyte instruction (o interaction with the blood)
50
After maturation and instruction of thymocyte in the cortex, what happens?
IF recognition of MHC I/II by CD4/CD8 molecules present by the APC it is positively selected and sent to the medulla as a immuno-competent naive T cell
IF not, then pruning by anergy or apoptosis
IF recognition of self antigens presented by APC undergoes negative election and is pruned. IF not, then migrates to medulla
51
Describe positive selection in the thymus cortex
Recognition of SELF-MHC I/II by CD4/CD8 molecules presented by APC results in positive selection and sent to medulla
IF fails it is pruned
52
Describe negative selection in the thymus cortex
IF recognition of self-antigens presented by APC then the thymocyte is pruned
IF not, sent to the medulla as immuno-competent naive T cell
53
What percent of thymocytes survive to be immunocompetent naive T-cells?
2 %
| This is why the medulla of the thymus stains light
54
What color does the medulla stain in the thymus?
Light due to few thymocytes
55
After making it to the medulla, what happens to the immunocompetent naive T cells?
Exit the medulla via venules and efferent lymphatic vessels to migrate to secondary lymphatic organs
56
What is anergy?
Failure to separate, no clonal expansion
57
What are Hassall's corpuscles?
Type VI reticular cells in whirl-shape that are located in the medulla of the thymus
58
What is the function of MHC?
Regions on the cell that contains antigen presenting proteins on the cell surface
May be referred to as HLA (human leukocyte antigen)
For us HLA=MHC
59
What stimulate thymic matruration of T-cells?
hormones produced by epithelial reticular cells
60
Describe thymic testing
Test ability of nascent T cells to recognize HLA I/II molecules and self-epitopes which is mediated by Type II/III epithelial reticular cells and bone marrow dendritic APCs
61
The T cell receptor complex (TCR) is composted of what?
CD3 and wither CD4 or CD8
62
Helper T cells have what MHC? Cytotoxic T cells?
Helper - CD4
| Cytotoxic - CD8
63
The TCR can recognize an epitope antigen if it is?
Bound to an MHC molecule - MHC restricted
| Role of APC!
64
What is unique about APC?
Can express both HLA I and II
| Most nucleated cells express just HLA I
65
What is the function of the blood thymus barrier?
Isolates thymocytes from exposure to foreign antigens / blood-borne macromolecules therefore T cells exit the medulla as naive immunocompetent mature lymphocytes.
Exclusively located in the thymus cortex
66
Describe the vasculature in the thymus
Vessels do not gain access to the cortex directly but do so from the trabeculae and enter the corticomedullary junction where thy form capillary beds that penetrate the cortex
Self-macromolecules are allowed to cross in order to participate in T-cell education and development of self-tolerance
67
The capillary layers in the thymus are composed of...?
Continuous endothelium
Perivascular connective tissue and basement membrane
Epithelial reticular sheath
68
T or F: Encountering self HLA in the thymus is critical for T cell education and required for the rescue from anergy/apoptosis
T, if too affined toward the self antigens they are pruned
69
What is thymic involution?
As age, the thymus parenchyma is replaced by adipocytes
70
Life of WBC neutophils
Circulate freely in the blood stream, often first responders, contribute to inflammation, last 6 hrs to 2 days (thought to prevent virus use to reproduce via infection)
71
Life of eosinophil
Allergic response, help to identify foreign substances or trigger asthma related symptoms, circulate 8-12 hours before settling in tissue where they live for 8-12 days
72
Life of basophils
Play big role in inflammatory response, especially for allergies because they contain histamine (inc blood flow) and heparin (prevent blood clotting) Last for 4 hrs to 5 days.
73
Life of lymphocytes
Large (NK cells), Small (Helper and cytotoxic T cells, B cells)
NK cells destroy both tumors and infected cells and live up to 2 weeks
Helper T cells record information of newly-encountered antigens and release cytokines to attract cytotoxic T cells when antigen reappears. Lasts only about 26 weeks! Although memory is preserved through division.
Cytotoxic T cells last anywhere from 1 year to live.
B cells secrete antibodies that stick to antigens in effect marking them for killer cells to destroy. Vary widely in life span from 10 days to 15 months
74
Life of monocytes
Precursor cells for macrophages and dendritic cells
| Stored in spleen,monocytes enter blood upon infection and differentiate at the site of infection. Lasts several months
75
Life of platelets
Small cells that form blood clots and seal broken blood vessels.
average life is between 9-12 days.
76
Which cells undergo V(D)J recombination?
T and B cells to make variety (in thymus and bone marrow respectively)
Natural killer cells do not
77
What lymphatic organs are encapsulated?
Thymus, lymph nodes, spleen
78
Describe lymph nodes
Secondary (peripheral) lymphoid organs
Small (<3 cm in diameter)
Encapsulated with fibrous CT in oval shaped structures interposed in the path of lymph vessels
Parenchyma is composed of T and B cells, APCs, and macrophages
FUNCTIONs to distribute mature lymphoid cells.
79
Lymph nodes are responsible for providing an environment to?
Allow immunocompetent cells to interact with each other, antigens, and with other cells to mount an immune response against pathogens
80
2 functions of lymph nodes
1) lymph filtration to remove bacteria and foreign substances from the lymph via resident macrophages in the sinuses
2) Antigen presentation and recognition
APCs that contact antigens migrate to the nearest lymph node and present their epitope-MHC complex to the lymphocytes
If an antigen is recognized and a B cell becomes activated, that B cell migrates to a primary lymphoid nodule and proliferates forming a germinal center and a secondary lymphoid nodule
81
Describe the capsule of a lymph node
Dense connective collageous tissue surrounding the node
Contributes to the 3D structure of the node cortex via trabeculae
Subdivides the outer region of the cortex into incomplete compartments
82
The capsule and trabeculae combine to make?
The reticular CT that forms the architectural framework of the node
83
Describe the path of lymph upon entering a lymph node
Enters via an afferent lymphatic vessel (located on the convex side of the node and has valves to prevent back blow)
Then to subcapsular sinus
Then to cortical sinus (also called trabecular or paratrabecular sinus)
Then to medullary sinus
Then to efferent lymphatic vessel (exit on the hillum, valves also present)
84
Describe lymph circulation
Not closed, no central pump.
Occurs with low pressure mainly on the movement of skeletal muscle to squeeze fluid. Lymph flows only one way via valves (semilunar)
85
How do T and B lymphocytes enter the lymph node
Enter via the paracortex from vasculature via endothelial venules
86
After entering the paracortex in lymph nodes, what happens to B cells?
Migrate to the cortex in primary lymphoid nodules
87
What happens to T cells upon entering the paracortex of the lymph node?
Stay in paracortex
88
Cells are activate via MHC-epitope presentation in the lymph node, what happens?
Proliferate and form secondary lymphoid nodules. New memory and plasma B cells exit the secondary lymphoid nodules
89
Upon leaving the secondary lymphoid nodules, what happens to B cells?
Majority migrate to the medulla and form medullary cords. Then migrate to the medullary sinuses and exit via efferent lymphatic vessels
90
What happens to B cells that leave the efferent lymphatic vessels?
Majority of plasma B cells migrate to the bone marrow and produce antibodies
Majority of memory B cells take up residence in other secondary lymphatic organs
91
10% of new plasma B cells do what?
Stay in the medulla and release antibodies into the medullary sinus (instead of exiting)
92
What is the thymus dependent region of the lymph node?
Paracortex
93
DCs and APCs migrate to the paracortex and present antigen to T cells via MHC epitope complexes and...
If T cells are activated they profilerate and expand the paracortex depth (swollen lymph nodes as in infection
The new T cells exit the paracortex and migrate to the medullary sinuses and exit via the efferent lymphatic vessels
94
High endothelial venules are the point of entry for B and T cells in the lymph node and are located in the?
Paracortex
95
Lymphoid nodules in lymph node are aggregates of B cells located in?
The cortex
96
What is the mantle zone (corona)?
Peripheral to a germinal center, dense accumulation of B lymphocytes migrating out from the germinal center
97
What is a germinal center?
```
Where B cells (centroblasts) proliferate, migrate, express slgs, switch immunoglobin class, and are exposed to antigen bearing follicular dendritic cells
B cells (centrocytes) that do not synthesize proper slgs undergo apoptosis and are eaten by macrophages
Surviving cells exit the secondary nodule as memory B cells or plasma cells and migrate to the medullary sinus
```
98
Function of the dark zone of the geminal center of the secondary lymphoid nodule
Naive B cell entry, clonal expansion, and somatic hypermutation
99
Function of light zone in the geminal center of a secondary lymphoid nodule
```
Apoptotic B cell due to disadventageous mutation
Improved affinity of cells are selected by DCs and differentiaton and class switching to plasma or memory B cells occurs here
```
100
A secondary lymphoid nodule is composed of?
Geminal center and mantle zone
101
Medullary sinuses are point of exit for B and T cells located in the?
Medulla
102
What is the spleen?
Secondary lymphoid organ
Largest encapsulated lymphoid organ in the body
Located in the upper left quadrant of the abdominal cavity
103
Functions of the spleen?
Filters blood
Forms lymphoid cells (T and B cell profileration)
Eliminates or inactivates blood-borne antigens
Destroys aged platelets and erythrocytes
Participates in fetal hematopoiesis
Can resume hematopoietic function in the adult
104
Describe spleen structure
Capsule of collagenous connective tissue
Trabeculae that arise from the capsule and guide blood vessels
Hilum (concave surface) as in lymph nodes which is the entry point of arteries and accompanying nerve fibers
The capsule and trabeculae suspend the reticular connective tissue that forms the architectural framework of the organ
105
Describe the path of blood into the spleen for filtration
Splenic artery enters at the hilum
Then to trabecular artery
Then to central arteries (above and including makes up the white pulp)
Then into the pencillar arteries in the red pulp
106
What vasculature is present in the white pulp of the spleen?
Splenic artery, trabecular artery, and central arteries
107
From the pencillar artery, where does blood go?
To the pulp arterioles, terminal arterial capillaries, and macrphage sheathed arterioles
108
Where is the central artery in the spleen?
In the center of the periarterial lymphatic sheath (PALS), it branches but maintains the PALS until it leaves the white pulp to form the pencillar arteries
109
The terminal arterial capillaries split to?
Open circulation in the open ended vessels in the splenic cords of bilroth
Closed circulation to the splenic sinuses then to pulp veins then to trabecular veins then to splenic vein and exits at the hilum
110
What is the red pulp? What is function?
Appears as red areas surrounding greyish areas (white pulp) in FRESH cut spleen secitions.
In combination with the marginal zone / marginal sinuses, macrophages and phagocytes in the red pulp filter the blood removing microorganisms and aged RBC and platelets
111
What composes the red pulp?
Splenic sinuses and splenic cords of bilroth
112
What are splenic sinuses?
Located in red pulp and are spaces with discontinuous basal lamina
113
What are the splenic cords of bilroth?
Sponge material in the red pulp of spleen composed of a loose network of reticular fibers
114
Where do T and B lymphocytes enter the spleen?
At the marginal zone, where the marginal sinuses contain cells/antigens from the blood, first contact of APCs, B cells, T cells
115
After entering the marginal zone, where do T and B cells go?
To the white pulp (contains all the spleen's lymphoid cells/tissue)
116
From the white pulp, where do T and B lymphocytes go in the spleen?
To the PALS (periarterial lymphatic sheath)
117
Once in the PALS, what happens to the B and T cells?
B cells migrate to the lymphoid nodules within the PALS
| T cells stay in the PALS
118
Once in the lymphoid nodule, what do B cells do?
The lymphoid nodule displaces the central arterole to a peripheral position
If B cells are activated via MHC-epitope, they proliferate ad form secondary lymphoid nodules and new memory and plasma B cells exit the secondary lymphoid nodules
119
Once in PALS, what do T cells do?
If activated via MHC-epitope presentation they proliferate and exit the spleen via the marginal sinuses located in the marginal zone and migrate to the site of antigen challenge or just join the circulating lymphocyte pool
120
T and B cells exit the spleen via??
The marginal sinuses located in the marginal zone
121
What is the white pulp?
Appears greyish in fresh cut spleen sections
Part of the infection fighting immune system
Produces lymphocytes (B and T cells) and antibodies
122
What composes the white pulp?
Lymphoid nodules and PALS
123
What is the marginal zone?
Surrounds white pulp and separates it from the red pulp
124
What does the marginal zone of spleen contain?
Marginal sinuses, capillary loops at which blood-borne cells, antigens, and particulates first contact the splenic parenchyma
Contains plasma cells, T cells, B cells, macrophages, and dendritic APCs
125
What happens in the marginal zone?
Macrophage phagocytosis of antigens, bacteria, foreign particles, and old RBC/platelets
APCs sample the blood for antigens and macrophages attack pathogens
Circulating T and B cells entering the blood and migrating to the white pulp can contact APCs for epitope-MHC complex presentation and activation
126
What is MALT??
Mucosal-associated lymphoid tissue
Non-encapsulated localized lymphocyte infiltration and lymphoid nodules in the mucosa of the GI, respiratory, and urinary tracts
127
What is the function of MALT?
Response to airborne/ingested antigens
128
Three principal examples of MALT
GALT - gut-associated lymphoid tissue
BALT - bronchus-associated lymphoid tissue
Tonsils
129
GALT is primarily composed of?
Lymphoid follicles along the length of the GI tract, generally isolated from one another
130
What are Peyer's patches?
Prominent accumulation of GALT in the ileum where GALT forms aggregates composed of B cells surrounded by a looser region of T cells and APC
131
T or F: Afferent lymph vessels are absent in GALT
T, but there is efferent lymph drainage
132
What are M cells (microfold cells)?
Located in the epithelial lining adjacent to the lymphoid follicles in the ileum and thought to capture antigens and transfer them to macrophages located in Peyer's patches
133
What is BALT?
Similar to Peyer's patches, but located int he walls of bronchi
134
T or F: There are no afferent lymph vessels in BALT
T, just efferent lymph drainage
135
What makes up BALT?
B cells are majority, but also APCs and T cells
| M cells are also present in epithelium of bronchi and are thought to transfer antigens to macrophages within the BALT
136
What is the tonsil?
Incompletely encapsulated aggregates of lymphoid nodules that guard the entrance of the oral pharynx to be interposed in the path of airborne and ingested antigens
137
How do tonsils react to pathogens?
Lymphocyte proliferation mounting an immune response
138
What are the three types of tonsil?
Palatine, pharyngeal, and lingual
139
Where is the palatine tonsil found?
The boundary of the oral cavity and oral pharynx (aka at the back of throat)
140
Describe the structure of the palatine tonsil
A dense fibrous capsule separates the deep aspect of the tonsil from the surrounding connective tissue (incompletely encapsulated)
Superficial aspect is covered by an epithelial layer that dips into 10-12 crypts which invaginate the tonsilar parenchyma
141
What composes the parenchyma of the palatine tonsil?
Composed f lymphoid nodules many of which display germinal centers (indicative of B cell activation by antigen and subsequent proliferation)
