Lymphoid Histo (Lecture) Flashcards
1
Q
What is the main cellular constituent of the lymph system?
A
Lymphocytes
2
Q
What does is mean that most lymphocytes are recirculating and immunocompetent?
A
Recirculating - They travel through the blood and lymphatic vessels between differend sites of lymphoid tissue
Immunocompetent - have developed ability to recognize and respond to a single specific foreign antigen.
3
Q
What is the purpose of recirculation?
A
ensures the correct lymphocytes will encounter and destroy the right foreign antigens
4
Q
What do T lymphocytes do?
A
- Only recognize antigens that are presented to them
- Involved in cell mediated immunity
5
Q
What do B lymphocytes do?
A
- They Bind the antigen
- Humoral Immunity (antiBody production)
- can differentiate into plasma cells
6
Q
What type of cells are required for B cell proliferation and differentiation?
A
- Helper T Cells
7
Q
What type of cell differentiates into a plasma cell?
A
- B lymphocyte (with the help of a Helper T)
8
Q
T or F: plasma cells secrete antibodies
A
True
9
Q
T or F: T and B lymphocytes can be differentiated with H and E staining.
A
False
-Can only be told apart using immunocytochemical staining techniques
10
Q
T or F: T and B lymphocytes differ in location and function
A
True
11
Q
Macrophages:
Derived from?
Characteristics?
Purpose?
A
- Derived from monocytes
- Extensive processes that survey the environment
- Use phagocytosis to remove:
1. antigens
2. particulate matter
3. dead cells
12
Q
T or F: Dendritic cells, like macrophages, have extensive processes that survey the environment and they cannot be distinguished from macrophages using H and E.
A
True
13
Q
Describe the processes of antigen presentation
A
- antigen is broken down into peptide fragments
- presented on surface of T cells together with class I or II MHC molecules
- B cells, Macrophages, and Dendritic cells can present the antigen
14
Q
Describe the location of hematopoiesis in chronological order.
A
- Extraembryonic mesoderm of yolk sac
- Fetal liver
- Spleen
- Bone Marrow
15
Q
What are the two major lineages of progenitors that hematopoietic stem cells can give rise to?
A
- Myeloid
2. Lymphoid
16
Q
What are the two places that Lymphoid progenitor cells can migrate in humans?
A
- Thymus to differentiate into T-cells
2. Bone Marrow to differentiate into B Cells
17
Q
T or F: lymphocytes most commonly encounter foreign antigens in the primary lymphoid organs
A
False, Lymphocytes migrate from primary lymphoid organs (bone marrow and thymus) to secondary lymphoid organs where they encounter antigens
18
Q
What is the site where foreign antigens are captured and immune responses are mounted to trap and destroy the antigens?
A
Secondary Lymphoid Structures
Note: These are positioned and organized to capture foreign antigens that enter the body through a particular site
19
Q
T or F: immune responses involve lymphocyte proliferation and differentiation of T cells into plasma cells
A
FALSE, it involves proliferation and differentiation of B cells into Plasma cells
20
Q
What are the 4 secondary lymphoid structures?
A
- MALT
- Tonsils
- Lymph Nodes
- Spleen
21
Q
What is MALT?
A
Mucosa-Associated Lymphoid Tissue
consists of:
- diffuse lymphoid of lymphatic tissue
- isolated lymphoid nodules/follicles
- permanent aggregates of lymphoid nodules
22
Q
What are some examples of MALT that consists of permanent aggregates of lymphoid nodules?
A
- appendix
- peyer’s patches
23
Q
What secondary lymph structure is responsible for catching antigens traveling in the blood?
A
Spleen
24
Q
What secondary lymph structure is responsible for catching antigens traveling through the mouth and nose?
A
Tonsils
25
What secondary lymph structure is responsible for catching antigens traveling in lymph?
lymph nodes
26
What is the difference in a primary and secondary lymph nodule?
secondary nodules have a darker outer region and an inner lighter region
27
What is a primary lymph nodule?
- accumulations or small lymphocytes
| - appear dark blue in H and E because cells are tightly packed have lot of heterochromatin
28
What is a secondary lymph nodule and when is it formed?
- formed after exposure to an antigen and are in the processes of mounting an immune response
- Outer dark staining cortex or mantle with mostly SMALL lymphocytes
- Lighter staining germinal center or reaction center containing LARGE lymphocytes with more dispersed euchromatin, plasma cells, and macrophages. MORE B CELLS THAN T CELLS IN THE GERMINAL CENTER
29
What is the major difference in dendritic cells and macrophages?
Dendritic cells do no phagocytose
30
What are 3 types of antigen presenting cells?
- Macrophages
- Dendritic Cells
- B cels
31
What provides the supporting framework for lymphocytes?
Reticular fibers
32
What is GALT and BALT?
- Gut Associated Lymphoid Tissue
- Bronchial Associated Lymphoid Tissue
-These are different forms of MALT
33
What is the most common site of entry for microorganisms?
digestive, respiratory, and urogentital tracts
34
T or F: MALT constitutes the vast majority of the body's lymph tissue
True (contitutes ~85%)
35
Lymphocytes and plasma cells in the lamina propria of the small intestine is an example of what type of lymphoid tissue?
Diffuse lymphoid tissue
36
What type of permanent lymph aggregate is specific to the ileum? Describe this tissue.
peyers patches
- 30 patches w/ 10-70 nodules
- associated with MICROFOLD cells in overlying epithelium
37
Describe the manner in which antigens are combated in Peyers patches.
1. M CELLS (intestinal lumen) endocytose bacteria and proteins
2. antigens are transported across the cell and discharged into underlying tissue
3. Lymphocytes, dendritic cells, and macrophages reside in this underlying tissue
38
T or F: tonsils are considered part of MALT
True
39
What are the two parts of lymphoid organs, which of these parts is functional?
Stroma
| Parenchyma - FUNCTIONAL
40
Name and describe the parts of the stroma in lymphoid organs.
Stroma:
1. Capsule - dense irregular CT (surrounds organ)
2. Septa/trabeculae - dense irregular CT (extends in from capsule)
3. Reticular Fibers - form a meshlike network to support lymphocytes
41
What does the parenchyma of lymphoid organs consist of?
- lymphoid nodules
- lymphoid tissue
NOTE: this is organized different ways in different organs
42
What are the 3 lymphoid organs?
Tonsils (pt. of MALT)
Lymph Node
Spleen
43
What are the 3 types of tonsils and what is their location?
- Palatine (the 'tonsils')- either side of the pharynx
- Pharyngeal (adrenoids) - roof of pharynx
- lingual - base of the tongue
44
Describe the stroma of palatine tonsils.
1. Half capsule - along base of tonsils where tonsils attach to wall of pharynx septa
2. Septa
3. Reticular fibers
45
Describe the parenchyma of palatine tonsils.
Contains lymph tissue and nodules
46
What type of tissue makes up the capsule of the palatine tonsils? Describe some defining features.
- non-keratinized stratified squamous epithelium
- TONSILLAR crypts - deep extensions from surface epithelium
- kept moist by the secretions from mucous glands
47
What causes palatine tonsils to easily become infected?
- no clear border between epithelium and parenchyma
| - why? lymphocytes erode into the covering of the palatine tonsils
48
Where do lymphatic vessels begin?
- Loose CT of:
1. Skin
2. Mucosa
49
T or F: lymph nodes can be found along the course of smaller lymph vessels.
False, found on larger lymph vessels
50
What does the stroma of lymph nodes consist of?
- capsule
- septa
- reticular fibers
51
What does the parenchyma of lymph nodes consist of?
Parenchyma:
1. Cortex
- outer cortex
- paracortex or deep cortex
2. Medulla
- medullary cords
- medullary sinuses
52
What is contained in the:
1. Outer Cortex
2. Paracortex
3. Medullary Cord
Note: these are given from outermost to innermost
1. Outer Cortex:
- lymphoid nodules of B CELLS
- plasma cells from differentiated B CELLS
- Macrophages
2. Paracortex:
- lymphoid tissue
- T CELLS
3. Medullary Cord:
- B CELLS
- Plasma Cells
- Macrophages
53
Describe the flow of lymph through a lymph node.
1. Afferent Lymphatic Vessel
2. Cortical (subscapular) sinus
3. Trabecular Sinus
4. Medullary Sinus
5. Efferent Lymphatic Vessel
54
Describe lymphatic sinuses
Open and Leaky
- Endothelial lining facing parenchyma = discontinuous
- Plasma cells secrete antibodies that enter lymph sinuses
- Macrophages send processes into sinuses to monitor lymph
55
Describe the processes of filtering as lymph percolates through the lymph node.
1. Macrophages phagocytose particulate matter
| 2. Antigen trapped and presented to T cells
56
How do lymphocytes enter lymph nodes?
Primarily through Blood Supply
57
What type of cell lines post-capillary venules in the paracortex and what is special about these cells?
- lined by high cuboidal endothelial cell
| - express surface receptors that recognize lymphocytes
58
How do lymphocytes exit HEVs and where do they migrate follows this escape?
Diapedesis
- B Cells migrate to outer cortex and medullary cords
- T Cells migrate to the paracortex
59
What ensures that lymphocytes will encounter foreign antigens that have been trapped in lymph nodes?
Lymphocyte Recirculation
60
What does the stroma of the spleen consist of?
- Myofibroblasts and Mesothelium
- Trabeculae
- Reticular fibers
61
What does the parenchyma of the spleen consist of?
- Islands of White pulp (lymphatic tissue)
(note: this appear blue in H and E)
- Red Pulp - contains RBCs
62
What does the WHITE PULP consist of?
1. Periarterial Lymphatic Sheath (PALS) - lymphoid tissue rich in T-Cells, surrounding Central Artery
2. Splenic (lymhpatic) nodules - characterized by a branch of the central artery located off center
63
What does the MARGINAL ZONE consist of?
- lymphoid tissue at the border between white and red pulp
64
What does the RED PULP consist of?
1. Splenic cords - cords of billroth - strands of lymphatic tissue
2. Splenic (venous) sinuses
65
T or F: immune responses against antigens in the blood are mounted in the red pulp.
False, immune responses are mounted in the white pulp of the spleen
66
Where in the spleen is particulate matter and cellular debris in the blood ingested by macrophages?
Red pulp
67
Where is blood deposited in the spleen?
Red Pulp
68
Describe the OPEN SYSTEM of circulation in the spleen from the splenic artery onwards.
1. SPLENIC a. --> sends branches that travel in Trabeculae
2. TRABECULAR a. enter white pulp to become CENTRAL a.
3. CENTRAL a. goes through white pulp and red and branches into penicillar arteriorles and continues as sheathed capillaries
4. Sheated capillaries surrounded by macrophages
***MAIN PT. Capillaries end BLINDLY depositing blood into red pulp
69
What happens in the spleen once the capillary ends blindly depositing blood into the red pulp?
- Antigens are captured by MACROPHAGES and B CELLS from the red pulp and maginal zone
- Antigen is presented to T Cellsin the PALS
- B cells proliferate and secondary nodules form as response mounts
70
How does blood return to the vessels after being dumped into the spleen?
- RBCs pass between elongated endothelial cells that line VENOUS SINUSES
- Old RBCs aren't flexible, they get stuck and are phagocytosed
71
What are the 4 functions of the spleen?
1. Trap and mount immune responses against antigens in the blood
2. Remove and phagocytose damages RBCs and platelets
3. Retrieve iron from Hb and store it
4. Hematopoiesis in fetal life
72
Does the thymus mount immune responses?
NO
73
T or F: the thymus is comprised of lymphoid nodules and follicles..
FALSE comprised of lobules
74
Describe the stroma of the thymus.
- Capsule
| - Septa - separate the thymus into lobules
75
Describe the staining structure and staining pattern of each lobule in the parenchyma.
Lobules consist of:
cortex - darker staining outer region
medulla - lighter staining inner region
76
What is the relationship between epithelioreticular cells and T Cells?
Epithelioreticular cells secrete factors that promote T-Cell differentiation
77
What happens to T-Cells that have not differentiated properly or that recognize self antigens?
They are phagocytosed by macrophages
78
What is present in the cortex of thymic lobules?
- T Cells and small and very densly pack macrophages
79
What is present in the medulla of thymic lobules?
- T Cells that are larger and less densly packed (Hassall's/Thymic corpuscles)
80
What distinguishes the thymus from all other lymphoid organs?
Hassall's/Thymic corpuscles
81
What do Hassall's/Thymic Corpuscles consist of?
Concentrically arranged epithelio-reticular cells
| - show signs of keritinizaiton and degeneration
82
Are epithelioreticular cells only present in medulla of thymic lobules?
no, there is just looser packing here so they can be more easily identified
83
When does T Cell proliferation and differentiation decreas?
In puberty
84
Describe the early stages of T Cell proliferation and differntiation.
- Starts in the thymus
- acquire specificity for a particular foreign antigen (aka EDUCATION)
- BLOOD-THYMIC BARRIER prevents foreign antigens from entering cortex
85
How is the blood-thymic barrier achieved?
Capllaries are ensheathed by 5 layers:
1. Endothelial cells joined by Tight Junctions
2. Basal lamina
3. Perivascular CT (w/ macrophages)
4. Basal lamina produced by epithelioreticular cells
5. Epithelioreticular cells
86
Where do T Cells go after they are differentiated?
- MIGRATE FROM CORTEX TO MEDULLA
| - T Cells recognizing self-antigens are elminated
87
What are the two fates of surviving T cells in the thymus?
CD8 cytotoxic T cells
| CD4 helper T cells
88
Where do mature T cells travel?
-Thymus Dependent regions of secondary lymph organs
89
What does removal of the thymus in early development result in?
impaired cell-mediated immunity
