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

2

1

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 non-

keratinized 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 1The region at the arrow is:

A) Peyer’s Patch

B) Germinal Center

C) Lymph Node

D) Primary lymphoid nodule

Question 1The 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 VesselsValves 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 ink- stained black.

Trabecular

Subcapsular

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

A

B

Question 2

C.Both

D.Neither

Q1) For the two pictures on the slide, select the correct answer for each of the below:

Is encapsulatedContains germinal centersPeripheral lymphoid tissueCentral lymphoid tissue

A

B

Question 2

C.Both

D.Neither

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)

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