Lymph I: The Peripheral Lymph System

Lymph I: The Peripheral Lymph System

Peripheral = Secondary Primary Immune Organs = bone marrow, thymus Site of maturation of cells of the immune system Secondary Immune Organs = Nodes, MALT, spleen Filter blood and lymph Site of antigen, immune system interaction

Lymph Vessels Valves Carries Lymph from tissue lymph nodes blood via thoracic duct Fluid Proteins Ingested fats Particulate matter Antigen Lab 11 Slide 7

Peripheral Lymph Organs Diffuse Eg. Peyer s patches, tonsils, appendix Non-encapsulated In GI, respiratory, GU, and tracts, tonsils, appendix Encapsulated Spleen, lymph nodes

The Follicle Primary - Lymphocytes Secondary - Germinal Center - Looks pale! - Antigen has been encountered Lab 11 Slide 9

Secondary Follicle Germinal Center Pale staining center: Plasmablasts = B cells Large, euchromatic nuclei Prominent nucleoli Mitotic activity Dark periphery T cells helping out Lab 11 Slide 15

Diffuse Lymphoid Tissue At most likely site of infection GALT = Gut Associated Lymphatic Tissue Prototype for diffuse lymphatics: S/B/MALT Lab 11 Slide 4

GALT Peyer s patches In lamina propria of GI No afferent lymphatics! Antigen enters via transcytosis across M cells Lab 11 Slide 4

Tonsils Diffuse Lymph organs! Not encapsulated! You may see stratified, squamous nonkeratinized epithelium. Lab 11 Slide 1

Encapsulated Lymphoid Tissue Eg. Spleen, Lymph nodes Both afferent and Efferent lymphatics Lab 11 Slide 5

Lymph Node Architecture Capsule: DICT (collagen I is red/brown in silver stain) with trabeculae that extend into stroma of node (collagen III is black/brown) Subcapular space with macrophages (visualized with India ink) Cortex Germinal centers w/ B cells Paracortex around follicles Deep cortex w/ high endothelial venules Juxtamedullary cortex Medulla w/ Plasma cells and Macrophages Cords Sinuses Hilum Efferent lymphatics Afferent and efferent bvv Lab 11 Slide 14

Lymph Node Architecture Capsule: DICT (collagen I is red/brown in silver stain) with trabeculae that extend into stroma of node (collagen III is black/brown) Subcapular space with macrophages (visualized with India ink) Cortex Germinal centers w/ B cells Paracortex around follicles Deep cortex w/ high endothelial venules Juxtamedullary cortex Medulla w/ Plasma cells and Macrophages Cords Sinuses Hilum Efferent lymphatics Afferent and efferent bvv Lab 11 Slide 6

Lymph Node Architecture Capsule: DICT (collagen I is red/brown in silver stain) with trabeculae that extend into stroma of node (collagen III is black/brown) Subcapular space with macrophages (visualized with India ink) Cortex Germinal centers w/ B cells Paracortex around follicles Deep cortex w/ high endothelial venules Juxtamedullary cortex Medulla w/ Plasma cells and Macrophages Cords Sinuses Hilum Efferent lymphatics Afferent and efferent bvv Lab 11 Slide 12

Lymph Node Flow Afferent Lymphatics Subcapsular sinus trabecular sinuses medullary sinus efferent lymphatics Lab 11 Slide 5 Lab 11 Slide 14

Thymus and Spleen Are you getting immune to exam blocks yet??

Thymus= Education of T cells Thymocytes mature and proliferate in the thymus Thymocytes undergo positive and negative selection Only T cells that react weakly with self proteins survive

Thymus has 3 cell types Epithelioreticular cells are large, pale, and stellate (they are not reticular fibers!) Thymocytes are immature T cells Macrophages phagocytose T cells that react too strongly with self Thymocytes Epithelioreticular cells

Medulla Cortex The Cortex and Medulla The cortex stains darkly basophilic because there lots of small lymphocytes with intensely stained nuclei The medulla stains light because it has less lymphocytes with more cytoplasm

Blood-Thymic Barrier Separates developing T cells from blood (prevents T cells from recognizing foreign proteins as self ) Components (from outside) Capillary endothelium Endothelial basal lamina Perivascular connective tissue sheath Basal lamina of epithelioreticular cell Epithelioreticular sheath

Hassall s corpuscles Hassall s Corpuscles instantly signify the thymus!! They are concentrically arranged keratinizing and degenerating epitelioreticular cells and macrophages They are found in the medulla

The Adult Thymus Adult thymus shrinks Adipose tissue replaces thymic tissue Medulla and cortex are harder to differentiate because there are less lymphocytes

The Spleen: What is it good for? 1. Filters blood 2. Iron Retrieval 3. RBC reserve 4. Immune Response* 5. Fetal Hematopoiesis

The White Pulp Appears basophilic on H&E and red on silver stain Site where immune response is mounted; formation of germinal centers Germinal centers with B cells and B cell derivatives push the central artery off to the side

White Pulp Vasculature The central artery is found in the white pulp The central artery is surrounded by the PALS, which is T cells Penicilli branch from the central artery into the red pulp

Red Pulp Vasculature: Penicilli give rise to ellipsoids Ellipsoids are capillaries ensheathed by reticular cells and macrophages; their lumens are often occluded in histo sections Blood is filtered by macrophages through fenestrations in the sinusoids

Sinusoids See how the basal lamina is interrupted; evident with both stains

The Red Pulp Appears Red on H&E Composed of sinusoids and Cords of Billroth The cords are the parenchyma of the red pulp; they are composed of reticular tissue w/ macrophages, red blood cells, and lymphocytes

Silver Stain *Notice how reticular fibers are evident with silver stain and not H&E *Notice the difference in appearance with the two different stains

That s all folks We hope you got a good education (THYMUS) & that you filtered out what was important (SPLEEN)