Yixing Xu
Wednesday,
November 30, 2005
Central = Primary lymphoid tissue
• Site of maturation of the cells of the immune system
• Bone marrow
– B cells, monocytes, erythrocytes, granulocytes, and megakaryocytes
• Thymus
– T cells
Peripheral = Secondary lymphoid tissue
• Filter blood and lymph
• Site of antigen, immune system interaction
Peripheral = Secondary lymphoid tissue
• Diffuse lymphatic tissue
– Unencapsulated
– GI (Tonsils*, Peyer’s patches*, appendix); Respiratory
tract; Genitourinary
– Found in the lamina propria where pathogens are
likely to invade
• Lymph nodes
– Encapsulated
– Interposed btwn lymphatic vessels (only)
• Spleen lymphatic tissue
– Encapsulated
– Interposed btwn lymph and blood circulation
Follicle = Nodule
Primary follicle
- Naïve (B) Lymphocytes
- No germinal center
Secondary follicle
- Germinal Center
- Antigen has been
encountered
- Looks pale because of
plasmablasts: large
euchromatic nuclei
- Surrounded by T cells
1
2
Germinal Center
– Dark zone = densely
packed B lymphocytes
separated by reticular
cells
– Light zone = plasmablasts
• Large cell, central nucleus,
prominent nucleolus
– T cells at periphery
Tonsil
• Unencapsulated
• Stratified squamous nonkeratinized epithelium
• In the dense fibrous CT
• CT Septum  lobes
• Crypts - invaded by
lymphocytes
• Numerous Lymphoid
nodules
– Primary: homogeneous
– Secondary: germinal centers
• Lymphocytes invade
the epithelium and the
connective tissue
• GALT (gut associated lymphatic tissue)
– Unencapuslated: diffuse lymphatic tissue
– In the loose areolar CT of the lamina propria
– Solitary lymphatic nodules
• Aggregates of lymphatic nodules in Peyer’s patches and
appendix
Question 1
The region at the arrow is:
A) Peyer’s Patch
B) Germinal Center
C) Lymph Node
D) Primary lymphoid nodule
Question 1
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 Node Structural
Components
• Capsule: Dense, Irregular CT
(collagen type I stains red
brown)
• Trabeculae are extensions of
the capsule
• Reticular tissue - framework
(collagen III stains black with
the Silver stain)
• Hilum - efferent lymph; entry
and exit of blood vessels
Lymph Flow w/in Node
Afferent Lymphatics  subcapsular sinus  trabecular sinuses 
medullary sinus  efferent lymphatics
Lymph Vessels
Valves prevent backflow
• Carries Lymph from tissue
 lymph nodes blood via
thoracic duct
–
–
–
–
–
–
–
Fluid
Proteins
Ingested fats
Particulate matter
Antigen
Disease microorganisms
Cells (normal and cancerous)
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.
Subcapsular
Trabecular
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
Lymph Node Parenchyma
•
Cortex
– Primary, secondary nodules
– B cells
•
Deep cortex
– (aka paracortex,
juxtamedullary cortex, thymus
dependent cortex)
– No nodules
– T cells
•
Medullary cords
– Plasma cells synthesize and
release Abs into lymph flowing
through the sinuses.
T-cell Zone
• Comprises of Deep Cortex and
Paracortex
• Deep cortex: T and B cells
enter from the circulation via
HEV
– Post capillary venules with high
endothelial cells
Summary of Lymph Node flow
Lymph Flow w/in Node
Afferent Lymphatics  subcapsular sinus  trabecular sinuses 
medullary sinus  efferent lymphatics
Question 2
C. Both
D. Neither
A
Q1) For the two pictures on
the slide, select the
correct answer for each of
the below:
Is encapsulated
Contains germinal centers
Peripheral lymphoid tissue
Central lymphoid tissue
B
Question 2
C. Both
D. Neither
A
Q1) For the two pictures on
the slide, select the
correct answer for each of
the below:
Is encapsulated (B)
Contains germinal centers (C)
Peripheral lymphoid tissue (C)
Central lymphoid tissue (D)
B
Question 3
The region inside the box
contains which of the
following upon antigenic
stimulation:
A. Plasma Cells
B. Macrophages
C. T-Cells
D. Memory B-Cells
E. All of the Above
Question 3
The region inside the box
contains which of the
following upon antigenic
stimulation:
A. Plasma Cells
B. Macrophages
C. T-Cells
D. Memory B-Cells
E. All of the Above