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 Lab 11 Slide 9 1 2

Germinal Center –Dark zone = densely packed lymphocytes separated by reticular cells –Light zone = plasmablasts –T cells at periphery

Tonsil Unencapsulated Stratified squamous non- keratinized 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)

A B Question 1 C.Both D.Neither

A B Question 1 C.Both D.Neither Tonsil Lymph node Is encapsulated = B Contains germinal centers = C Peripheral lymphoid tissue = C Central lymphoid tissue = D

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 ink- stained 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