jeanne a pawitan histology of the immune (lymphoid, lymphatic) system jeanne adiwinata pawitan dept....
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Histology of the immune (lymphoid, lymphatic) system
• Jeanne Adiwinata Pawitan
• Dept. of Histology
• FMUI
Immune system
• Cells of the immune system
• Bone marrow (myeloid tissue)
• Diffuse lymphoid system° Diffuse lymphoid tissue° Lymph (lymphoid) nodules
• Lymphoid organs - capsule
Immune system – defense mechanism
• Function: protection >< foreign elements° Foreign macromolecules° Invasive microorganisms• Viruses
• Bacteria
• Others
° Transformed cells
Defence mechanism (Martini)
• Non specific defenses° Physical barriers° Phagocytes (M, neutro, eosinophils, monocytes)° Immunological surveillance: NK cells° Interferons, complement system° Inflammatory responses, fever
• Specific defenses – specific immunity –specific immune response° Innate (human >< animal disease, except AIDS)° Acquired
Immune response
• Specific recognition system (specific immune system)° Recognize self >< non self° Component • Cellular (lymphocytes B, T)• Soluble (Ig)
• Nonspecific (innate) effector system (non specific immune system)° Amplifies – function – specific system
Nonspecific immune system• Soluble component° Complement proteins (cytokines): lymphokines-
monokines: interleukines (ILs), interferons (IFNs), tumor necrosis factors (TNFs), transforming growth factors (TGFs), hematopoietic colony-stimulating factors (CSFs)
• Cellular component – phagocytes:° Blood: neutrophils, eosinophils, monocytes
° Tissue: macrophages (alveolar macrophages, Kupffer’s cells, synovial cells – joint cavities, perivascular microglial cells – CNS)
Bone marrow (red) – myeloid tissue
• Location: ° central (marrow, medullary) cavity – long bones
° Interstices (trabeculae) – spongy/cancelous bones
• Soft, gelatinous, highly vascular – cellular tissue• Function: hemopoiesis – 5th month prenatal• LM: ° vascular compartment (A., V., sinusoids)
° Intervening spaces • hemopoietic compartments – meshwork - islands of
hemopoietic cells
• Adventitial reticular cells, reticular fibers
Bone marrow cells• Hemopoietic cells° Blood cells – various stages° Macrophages – destroyed• Nuclei – erythrocytes precursors• Malformed cells• Excess cytoplasm
• Adventitial reticular cells ° By age 20 – adult: cytoplasm - accumulate fat • ≈ adipose cells – large – reduce hemopoietic
compartment yellow marrow
Diffuse lymphoid system• Non-encapsulated• Location: ° Lymphoid organs° Mucosa (lamina propria) – mucosa associated
lymphoid tissue (MALT)• Digestive system (Gut ALT): Peyer’s patches• Respiratory system (Bronchus ALT)• Urinary system
• Occur as° Diffuse lymphoid tissue = localized lymphocyte
infiltration° Lymphoid nodules (lymphonodulus)
Diffuse lymphoid tissue
• Consists of° Stroma • Reticular fibers – silver impregnation
• Reticular cells of mesenchymal origin – some are phagocytic ≈ fixed macrophages
° Lymphocytes ° Free macrophages° Plasma cells
Reticular cells
• Shape: elongate – stellate• Nucleus: ovoid – euchromatic• Cytoplasm:° Scanty° Acidophilic ° Contains• RER – few• Golgi complex – moderate-well developed• Fine filaments – bundles – at periphery
Lymph (lymphoid, lymphatic) nodule, lymphonodulus – lymphoid follicles
• =circumscribed-spherical/ovoid-closely packed-lymphocytes
• In diffuse lymphoid tissue• Location:° Lymph node –cortex° Spleen – white pulp° Tonsils ° Lamina propria (MALT): Peyer’s patches, etc.
Gut-associated lymphoid tissue• Isolated lymphoid follicles• Peyer’s patches – aggregates – ileum° Lymphoid follicles
• B cells• T cells – looser – surrounding B Cells• Numerous APC – surrounding B cells
° Simple columnar epithelium M (microfold) cells – capture Ag present their epitopes to lymphocytes
° Afferent lymph vessels (-), ° Efferent lymph drainage (+)° Received small arterioles capillary bed high
endothelial lined venules (HEVs)° Lymphocytes entering Peyer’s patches have homing
receptors – specific for HEVs of GALT
Bronchus-associated lymphoid tissue
• ≈ Peyer’s patches – walls – bronchus – esp. bronchi-bronchiole bifurcate
• Epithelial cover: pseudostratified ciliated columnar epithelium with goblet cells M cells
• Afferent lymph vessels (-)• Efferent lymph drainage (+)• Rich vascular supply HEVs° Possible systemic and localized role in immune
response° Lymphocytes entering BALT have homing receptors
for HEVs of BALT
• Cells: mostly B cells, also APC, T cells
Lymphoid organs
• Thymus (primary lymphoid organ)
• Lymph nodes (lymphonodus)
• Spleen (lien)
• Tonsils (tonsila)
Thymus
• Location: superior mediatinum – anterior of great vessels (aorta)
• After puberty – involution (atrophy) → adult – adipose cells
• 2 lobes
• Encapsulated – dense-irregular-collagenous connective tissue septa (trabecula) – lobes incomplete lobules
Lymph node
• Location: interposed in the path of lymph vessels-esp.° Neck, axila, groin
° Along major vessel
° body cavities
• Functions:° Filter – remove
• Bacteria
• Foreign substances
Lymph node
• Small, soft, Ø < 3 cm
• Capsule – fibrous connective tissue (thickened at hilum) - trabeculae - adipose tissue
• Convex: afferent lymph vessels – valves
• Concave = hilum: A., V., efferent lymph vessels – valves ← medulla
Lymph node - sinuses
Sinuses: network – stellate reticular cells – macrophages – endothelial-like simple squamous epithelium – migratory lymphoid cells
Course:Afferent lymphatic vessels• Subcapsular sinus• Cortical (paratrabecular) sinuses• Medullary sinusesEfferent lymphatic vessels
Lymph node
• Histologically:° Cortex – antigen-presenting follicular
dendritic cells• Primary lymphoid nodules (virgin B & memory
B cells)• Secondary nodules (with germinal centers) –
antigenic challenge B memory & plasma cell
° Paracortex – Thymus dependent zone° Medulla
Lymph node - medulla
• Trabeculae – from hilum
• Medullary cords° Network – reticular fiber – reticular cells° Cells • Lymphocytes – migrating from cortex
medullary sinuses
• Plasma cells
• Macrophages
Lymph node - vascularization
• Artery (hilum) trabeculae medulla medullary cords ° Capillary beds in medulla° Cortex – cortical capillary beds
postcapillary venules (paracortex) vein - hilum
Spleen (lien)
• Largest lymphoid organ• Upper left quadrant – abdominal cavity • Intraperitoneal – visceral peritoneum• Function:° Proliferation B, T cells° Ab formation – blood-borne Ag inactivation° Elimination of Ag, bacteria, particles, etc.° Filtering blood – destroying old erythrocytes° Hemopoietic (fetal) – adult – when needed
Spleen (lien)
• Convex surface
• Concave surface – hilum – capsule-thickened° Arteries – nerve fibers (in)° Veins – lymph vessels (out)
• Dense – irregular connective tissue – capsule - occasional smooth muscle cells – trabeculae into the organ
Spleen (lien)
• Histology ° Network – reticular fibers – reticular cells –
attached to capsule trabeculae – blood vessels
° Fresh - cut - parenchyma• Grey area = white pulp
• (Marginal zone – 100 μm wide – between white – red pulp)
• Surrounding red area = red pulp (splenic cords of Billroth)
Spleen (lien) – blood supply
• Splenic artery - hilum branching trabecular arteries ( 0.2mm) central arteries – periarterial lymphatic sheath (PALS) ° Radiating - slender blood vessels red pulp (recur) -
marginal sinuses – marginal zone
° branching penicillar arteries – red pulp: • Pulp arteriole
• Sheated arteriole – Schweigger-Seidel sheath – macrophages)
• Terminal arterial capillaries – splenic sinuses
• Veins of the pulp splenic vein portal vein
Closed circulation – open circ.
• Closed circulation° Endothelial lining: terminal arterial
capillaries –continuous - sinuses
• Open circulation° Terminal arterial capillaries – red pulp -
sinuses
• Combination of both
Spleen (lien) – white pulp
• Central arteriole
• PALS: ° T lymphocytes° Frequently: lymphoid nodules (B cells) –
germinal center = antigenic challenge central arteriole - periphery
Spleen (lien) – red pulp sponge° Spaces = splenic (venous) sinuses (sinusoids)
• Endothelial lining – fusiform staves of a barrel
• Between endothelial cells - spaces - 2-3 m
• Surrounded by reticular fibers (continuous with splenic cords) – thin strands ┴ longitudinal axis
• Have a discontinuous basal lamina
° Sponge material = splenic cords of Billroth• Reticular fibers (collagen III) – loose network – interstices
permeated by extravasated blood
• Stellate reticular cells – isolate coll III from blood >< platelet reaction to coll >< coagulation
• Macrophages particularly numerous near sinusoids
Spleen –histophysiology
• Macrophages ° Marginal sinuses – macrophage rich° Periphery of splenic sinuses Phagocytosis
Ag, bacteria, particulate matter, etc Old erythrocytes
Less fkexible (old, malaria) –cannot penetrate spaces between endothelium
Surface coat: sialic acid residue (-) galactose moieties exposed – induced phagocytosis
Spleen –histophysiology
• Lymphocytes -Ag challenge white pulp ° B memory cells, plasma cells – lymphoid nodules° T cells (various subcategories) – PALS
marginal sinuses ° Site of Ag challenge ° Circulating pool of lymphocytes° Plasma cells• Some stay in marginal zone Ab marginal sinuses
• Most bone marrow – Ab bone marrow sinuses
Tonsils: palatine, pharyngeal, lingual
• Incompletely encapsulated• Aggregates of lymphoid nodules• Guard the entrance of oral (oro)
pharynx• Exposed to ° Airborne Ag° Ingested Ag
• Reaction to Ag° Forming lymphocytes° Mounting immune response
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