Anne and Tresha
Thursday,
December 2, 2004
Central = Primary
lymphoid tissue
• Site of maturation of the cells of the immune system
• Thymus
– encapsulated
– T cells
• Bone marrow
– Bursal equivalent
– B cells, monocytes, erythrocytes, granulocytes, and megakaryocytes
Peripheral = Secondary
lymphoid tissue
• Filter blood and lymph
• Site of antigen, immune system interaction
Peripheral = Secondary lymphoid tissue
• Diffuse lymphatic tissue (Unencapsulated)
– Found in the lamina propria where pathogens
are likely to invade
– GI: Tonsils, Peyer’s patches, appendix;
Respiratory tract; GU
• Lymph nodes
– Encapsulated
– Interposed btwn lymphatic vessels (only)
• Spleen lymphatic tissue
– Encapsulated
– Interposed btwn lymph and blood circulation
Lymph Vessels
• Valves
• Carries Lymph from tissue
 lymph nodes blood via
thoracic duct
–
–
–
–
–
–
–
Fluid
Proteins
Ingested fats
Particulate matter
Antigen
Disease microorganisms
Cells (normal and cancerous)
Lab 11 Slide 7
Primary follicle
- Naïve Lymphocytes
- No germinal center
Secondary follicle
- Germinal Center
- Antigen has been
encountered
- Looks pale! - because
of plasmablasts
2
1
Lab 11 Slide 9
• Germinal Center
– Dark zone = densely
packed lymphocytes
separated by reticular
cells
– Light zone =
plasmablasts
– T cells at periphery
Tonsil
• Unencapsulated
• Stratified squamous nonkeratinized epithelium
• Dense fibrous CT
• CT Septum --> lobes
• Crypts - invaded by
lymphocytes
• Numerous Lymphoid
nodules
– Germinal centers
• Lymphocytes invade
the epithelium and the
connective tissue
• GALT (gut associated lymphatic tissue)
–
–
–
–
In the loose areolar CT of the lamina propria
Diffuse lymphatic tissue
Solitary lymphatic nodules
Aggregates of lymphatic nodules (Peyer’s patches
and appendix)
Question 1
C. Both
D. Neither
A
B
Question 1
C. Both
D. Neither
Tonsil
A
•
•
•
•
Is encapsulated = B
Contains germinal centers = C
Peripheral lymphoid tissue = C
Central lymphoid tissue = D
B
Lymph node
Question 2
The region at the arrow is:
A) Peyer’s Patch
B) Germinal Center
C) Lymph Node
D) Primary lymphoid nodule
Question 2
The region at the arrow is:
A) Peyer’s Patch
B) Germinal Center
C) Lymph Node
D) Primary lymphoid nodule
Lymph Node Function
• Filters lymphatic fluid
• Enhance antigen presentation
• Facilitate B-Cell Activation to
generate plasma cells and
memory B-cells
Lymph Flow w/in Node
Afferent Lymphatics  Subcapsular sinus  trabecular sinuses 
medullary sinus  efferent lymphatics
Lymph Node Structural
Components
• Capsule: Dense, Irregular CT
• Trabeculae are extensions of
the capsule
• Reticular cells- framework
(stain black with the Silver
stain)
• Hilum- efferent lymphs; entry
and exit of blood vessels
Lymph Node Parenchyma
•
Cortex
– Primary, secondary nodules
•
•
Deep cortex
(aka paracortex, juxtamedullary
cortex, thymus dependent cortex)
– No nodules
•
Medulla
– Cords and sinuses.
– Where plasma cells
synthesize and release Abs
into lymph flowing through the
sinuses.
Lymphatic Sinuses
•
Subcapsular sinus
–
Receive lymph from afferent
lymphatic vessels
•
Trabecular sinuses
–
•
•
Drain into medullary sinuses
Provide open communication
between lymphatic drainage
and parenchyma (macrophages
monitor lymph as it percolates
through; will phagocytose)
Macrophages take up India inkstained black.
The Germinal Center
•
Characterizes the 2ndary nodule
•
Pale staining center: plasmablasts
– Large cells, large nucleus,
prominent nucleolus
– May see mitotic figures
•
Dark outer zone
– Densely packed lymphocytes
(sp. B-cells)
T-Cell Zone
• Comprises Deep Cortex
and Paracortex
• Where T and B cells
enter from the circulation
• See post capillary
venules with high
endothelial cells
• B cells migrate, T cells
remain
Medullary Region
• Cords and Sinuses
• Cords: reticular cells,
lymphocytes,
plasmablasts, plasma
cells
• Antibody secreted into
efferent lymph
• Macrophages present
• Entry/Exit of blood
vessels, nerves, efferent
lymph
Summary of Lymph Node flow
Lymph Flow w/in Node
Afferent Lymphatics  Subcapsular sinus  trabecular sinuses 
medullary sinus  efferent lymphatics
Question 3
The region inside the box
contains which of the
following upon antigenic
stimulation:
A. Plasma Cells
A. Macrophages
B. T-Cells
C. Memory B-Cells
D. All of the Above